Sliiiii A HISTORY OF BIRDS P-PYCRAFT „ ,,,.iip. '^ U;Mt!,rH' -nT^ rtiKwybHH u tX LIBRIS ERNEST ALAN VAN VLECK FOR THE PEOPLE FOR EDVCATION FOR SCIENCE LIBRARY OF THE AMERICAN MUSEUM OF NATURAL HISTORY ANIMAL LIFE AN EVOLUTIONARY NATURAL HISTORY General Editor: W. P. PYCRAFT ZOOLOGICAL DEPARTMENT, BKITISH MUSEUM VOL. II A HISTORY OF BIRDS /'. % A HISTORY OF BIRDS BY W. P. PYGRAFT ZOOLOGICAL DEPABTMKNT, BRITISH MUSEUM J^ 5%^'L\0'L WITH AN INTRODUCTION BY Sir ray LANKESTER, K.G.B., F.R.S. AND NUMEROUS ILLUSTRATIONS AND DIAGRAMS METHUEN AND GO. 36 ESSEX STREET W, G, LONDON V>; First Published in 1910 CAROLO EDUARDO FAGAN PLURIMA ET JUCUNDISSImA '* ilRlMORiA li^lfe>lCr\tU3-^.ST HIC LII'.KR PREFACE MY aim in writing this book is to present the study of Bird Life from the point of view of the Evolutionist ; to set forth, in broad outline, the evidence now generally regarded as bearing on that most fascinating pro- blem, the birth and growth of the various types of birds — whether regarded as large groups, or as geographical races. The external beauty of form and colour which birds pre- sent, has so far proved a serious distraction, so that Ornitho- logists, captivated thereby, have paid but little heed to the possible factors to which these features are due. At any rate, since the master mind of Darwin himself laid the foundation for this wider study of Bird Life but little progress has been made. It is hoped, however, that this volume will prove a stimulus to renewed efforts to penetrate some, at least, of the many mysteries to which he called attention. The purpose of this book, then, is obviously to present the Study of Birds as one of living organisms, moulded in part by an inherent constitution, and in part by that " struggle for existence " which is the lot of every living thing — a struggle with environment, animate and inanimate. This being so, it is obvious that anything more than the barest account of ana- tomical details would be out of place here. True, these "anatomical details" are the essence of the whole matter, but though this be so their bearing on the question at issue, at present, is not measurable ; and accordingly those who seek in these pages for information of this kind will seek in vain. My expert critics will doubtless discover many omissions in this book. I am aware of many : but I have had perforce to select, and I have chosen those facts which seemed best to viii A HISTORY OF BIRDS serve my needs. Furthermore, I have written, not for the expert but rather for those who, like myself, have a keen love of birds — but who have so far had no opportunity of studying them from this point of view. My friends being all busy men I have not dared to trouble them with appeals for help in my self-imposed task, but I am deeply indebted to Professor J. Arthur Thomson for help in laying the foundations, and to Mr. H. Eliot Howard for kindly criticism on my work in the course of its progress. For many of the illustrations in these pages I am indebted to the courtesy of the Council of the Zoological and Linnean Societies, and of the Norfolk and Norwich Naturalists' Society. My thanks are also due to Mr. A. J. Bishop, Dr. Bumpus, Mr. J. G. Millais, Mr. A. R. Momber, the Hon. Walter Rothschild, Major Trevelyan, Miss E. L. Turner, and to Messrs. Black, Jack, Sotheran and Rowland Ward. Finally, I desire to accord my best thanks to my friend Mr. G. E. Lodge for his splendid interpretation of the themes illustrated by his brush ; these have never before been so vividly and realistically handled, and they should do much to bring home the lesson they are designed to teach. W. P. PYCRAFT London November, 1909 CONTENTS PAGE Preface - ■ - - vii List of Illustrations in the Text - - xv List of Plates xix Introduction - - xxiii List of Authors quoted xxxi CHAPTER I Introductory ------ --..--i General characters of structure — ^feathers, glands, the skeleton, the respiratory system, the lungs and air-sacs, the digestive system, the circulatory system, the muscular system, the nervous system, the senses. CHAPTER II Phylogenetic ----- 30 Birds and their position in the animal kingdom. Relationship to the reptiles, and the evidence thereof. Archagopteryx — the first bird. Hesperornis and early specialisation. Ichthyornis. The Pro-aves. CHAPTER III Phylogenetic (continued) — The Classification of Birds in Broad Outline — The Main Lines of the Evolution of the Class Ayes -------.--.-. 41 Archornithes and Neornithes. The position of the Ostrich tribe in the system. What the structure of the bony palate reveals. Palaeo- gnathae and Neognathae. The classification of the Paljeo- gnathse and of the Neognathae. A hypothetical ancestor. The Grebes and Divers, Penguins and Petrels, Steganopodous birds, the Accipitres, the Anseres, the Alectoromorphae, — the Game-birds, Cranes and Rails, Plovers, Pigeons, the " Coraciiform " birds; the Passeres. Numerical strength. CHAPTER IV CEcological 61 Peculiarities of distribution. Continuous and discontinuous areas. Zoo- geographical regions. The northern and southern hemispheres and the origin of life. Some British birds and the lessons they teach in regard to the migration of animal life from north to south. Factors in the formation of isolation areas. The haunts of birds. ix X A HISTORY OF BIRDS CHAPTER V PAGE Seasonal Life. Relations to Moisture, Temperature, etc., and to Periodic Changes in the Cosmosphere - 8n The bleaching effect of light. Desert forms. The effects of a saturated atmosphere. Arctic conditions. Size and latitude. Storms and drought. CHAPTER VI Migration - - 89 Kinds of migration. Routes. The height at which birds fly. Speed. Lighthouses and their influence. Erratic migration. Causes of migration. Meaning of migration. CHAPTER VH Relations to the Animate Environment ...... 106 Relation to plants. Birds and pollination. Birds and spread of seeds. Birds in relation to other animals. The perils of nestling birds. Birds and " civilisation ". 24 CHAPTER VIII Peculiar Interrelations ..----... Ostriches and Zebras. Rheas and Guanacos. Oxpecker and big Game. Egrets and Elephants. Bee-eaters and Bustards. Penguins, Alba- trosses and Petrels. Osprey and small birds. Chaffinch and Missel-thrush. Burrowing Owl and Prairie-dogs. Petrels and "Tuatera Lizard". Puffins and Rabbits. Skuas and Gulls. Frigate-birds and Gannets. Cuckoos and their dupes. The causes of parasitism. CHAPTER IX Phases of Social Life - - 135 Gregarious birds. Curious sleeping habits. Pelicans fishing. Wood- peckers and food stores. Significance of gregarious habits. CHAPTER X The Relations of the Sexes ^ - 143 The division of labour in nest-building. Manifestations of sexual activity. Forms of this activity. Plumage displays. "Sacaleli." Wind-bags and display. Tournaments. Weapons and their uses. Dancing. " Gardening." Song. Instrumental music. Where the sex role is reversed. CHAPTER XI Reproduction — Nidification 173 The first nest-builder. Origin of nests. Primitive nests. Burrowing. Simple nests. The nests of the Thrush tribe. Complex nests. Pensile nests. Mud nests. The remarkable nests of Tree-swifts. Colonies. Variability in nesting sites. Strange nesting sites. Nest-building and instinct. CONTENTS xi CHAPTER XII PAGE Reproduction — Concerning Eggs -------- 195 Number of eggs in a " clutch ", Shape of the egg. Size. Texture and thickness of the shell. Colours of eggs. Origin of the colours. Patterns of coloration. Colours of eggs in relation to classification. Coloration in relation to environment. White eggs and their mean- ing. Structure and composition of the egg. CHAPTER Xni Reproduction (continued) — Care of the Offspring .... 213 Brooding and " brood-spots ". Care for the sitting female. The remark- able case of the Hornbill. The brooding of the Emperor Penguin. Brooding of Egyptian Plover and of Megapodes. Forsaking eggs. Osprey and care of eggs. Transportation of eggs by parents. Pre- cautions against floods. CHAPTER XIV Care of Offspring (continued) 223 The care of the young undertaken by the male alone, and by the female alone, or by both parents. The remarkable case of the Sand-grouse in procuring water for their young. The strange case of the trans- portation of the young in the Woodcock. Feeding customs. Sanitation of the nest. The callousness of Eagles. The coloration of nestlings. CHAPTER XV Nestling Birds and what thev Teach 235 The differences between young birds and young reptiles. Nestling birds and the systematists. The clothing of nestlings. Primitive nest- lings. Precocious flight. Helpless nestlings. The coloration of nestling birds and its significance. CHAPTER XVI The Life-history of Birds — an CEcological Summary - - - 262 Embryology in outline. No hard-and-fast line between embryonic and post-embryonic characters. Plumage phases. Some puzzling facts with regard to adult characters. The plumage of Thrushes. Signs of maturity. Nuptial liveries. Coloration and its evolution. Moult- ing. Abrasion phenomena. The age of birds. Mortality. Play of birds. CHAPTER XVII Variation : Continuous and Discontinuous — Inter-breeding - - 291 Paucity of information on variation in birds. The work of J. A. Allen. Relation of variation to natural selection. Barrington's work. Colour variation. Dimorphism. Mutation. Albinism and Melan- ism. Swallows. xii A HISTORY OF BIRDS CHAPTER XVIII PAGE Acquired Characters — the Problem of Parental Modifications - 311 The remarkable case of the Hoatzin and the bearing thereof on the problem of parental modification. The results of feeding experi- ments, and changes of light and temperature on Flamingoes and Tanagers. CHAPTER XIX Natural Selection as Applied to Birds 318 The theory of " Natural Selection " applied to birds. Modes of selection. Inter-specific selection. Pigs and Penguins. Skuas and natural selection. Protective coloration. Winter whitening of Ptarmigan. Mimicry among birds. Protective resemblance and aggressive re- semblance. Importance of inter-specific selection on the evolution of species. Intra-selection. CHAPTER XX Artificial Selection - - - - 33 = The evolution of the domesticated races of Pigeons, Fowls, etc. Rever- sion of domesticated races to the wild, ancestral type. Physiological and morphological species. Fertility and the test of species. CHAPTER XXI Sexual Selection ------ 343 Darwin and the theory of sexual selection. The evidence on which his theory was based. Objections to the theory of Alfred Russel Wallace, and of H. Eliot Howard. Sexual selection in absence of secondary sexual characters. Consciousness in display of the effect produced, or to be produced. The factors which incite display. The part which sexual selection does play. CHAPTER XXII Isolation — Spatial and Physiological and Determinate Evolution - 354 Isolation and natural selection in evolution. Natural selection and the origin of species. Isolation and geographical distribution. Varia- tions blastogenic. Romanes and Isolation. Physiological selection. Inter-breeding species. Island forms. Species formation in high altitudes. Discriminate isolation. Determinate evolution. CHAPTER XXIII Structural and Functional Adaptations — Shape and Symmetry - 366 The factors determining shape. The remarkable asymmetry of Owls' ears. The wing. The shoulder-girdle and sternum. The pelvic girdle. The pelvic limb. Some puzzling features in the pelvis of Struthious birds. The pectineal process and its homologies. Types of feet. Feathers and adaptation to arboreal life. CONTENTS xiii CHAPTER XXIV PAGE Adaptations (continued) — Organs of Extreme Perfection - - - 400 The significance of certain peculiar modifications of the trachea. Re- ciprocity in development. The apparent over-elaboration of organs as illustrated by Woodpeckers and Kingfishers. Diastataxy. CHAPTER XXV Adaptations (continued) — ^The Alimentary Canal and Vascular Systems -- 411 The form of the beak in relation to the food. Modifications of the tongue. The alimentary canal. Modifications of the crop and gizzard. The convolutions of the intestines. Peculiarities of the vascular system. CHAPTER XXVI Convergent Evolution and Parallel Development - - - 439 The evolution of the Owls and diurnal birds of prey. Night-jars and Owls, Swifts and Swallows. The Cariama, Cranes and Storks. The Plover tribe and the Rails. Gulls and Petrels. The Diving Petrels and the Auks. The remarkable transformation of the skeleton in the Auks and Diving Petrels. Homoplasy a factor in the evolution of birds. The problem of the New World Vultures, LIST OF ILLUSTRATIONS IN THE TEXT ILLUSTRATION PAOE 1. Diagrams Illustrating the Structure of a Feather. (After Pycraft) 6 From The Book of Nature Study. 2. Contour Feathers (Pheasant and Emu) showing the Hypo- RHACHis OR After-shaft. (After Pycraft) 8 From The Book of Nature Study. 3. A Developing Filoplume showing the Rami which later dis- appear, and the Main Shaft which remains to form the " Filoplume ". (After Pycraft) 10 From The Transactions of the Linnean Society. 4. Pterylosis of Acanthidositta chloris showing the Feather Tracts. (After Pycraft) 13 By permission of the Editors of The Ibis. 5. Wing of a Bird, Slightly Diagrammatic, to show the Arrange- ment OF the " Quill " or " Flight-feathers ". (After Pycraft) - 13 6. Dissection showing the Lungs and Air-sacs of a Bird. (After Strasser) 18 7. Types of the C.«ca, or Blind Gut, of Rhea, Owl and Martineta Tinamou -----23 By permission of the Editors of The Ibis, and of the Zoological Society. 8. Skulls of Nestling Penguin and Emu to show the Sutures Dividing the Separate Elements of the Cranium - - - 31 From Specimens in the British Museum of Natural History. 9. Hip-girdles of a Dinosaur, an Embryo Bird and a Nestling Emu. (After Marsh) 33 10. The End of the Shank and Middle Bones of the Foot (Tarso- metatarsus) of a Young Bird Compared with the same Bones in an Adult Reptile (Dinosaur). (After Marsh) - 34 11. The Skeletons of Two Extinct Fossil Birds, Hesperornis and Ichthyornis 36 12. One of the Pro-Aves. (After Pycraft) 39 13. Restoration of Arch^opteryx. (After Pycraft) - - - - 42 XV xvi A HISTORY OF BIRDS ILLUSTRATION PAGE 14. Stages in the Evolution of the Avian Palate - - - - 44 15. Phylogenetic Tree of Descent ---.... 57 16. The Whale-Headed Stork [Balczniceps) 68 17. The Rufous Tinamou {Rhynchotus rufescens) ----- 75 18. Wing Feather of a Curlew showing the Initial Stages in the Disintegration of the White Parts : and a Portion of THE Quill Feather of a Gull showing the same Process - 81 19. Humming-bird Fertilising Flowers of Marcgravia Nepenthoides. (After Wallace) 106 20. Devices to Secure a Permanent Food Supply - . . - 141 21. Pouch of Great Bustard Dissected to show its Relation to the Gullet and Windpipe. (After Pycraft) 152 22. The Display of the Great Bustard [Otis tarda) - - - 153 From Newton's Dictionary of Birds. 23. Types of Windpipes .-.....-. 167 24. Nest of the H\mmer Head 178 From Newton's Dictionary of Birds. 25. Nest of the Humming-bird {Phoethornis eiirynome) - - - 182 From Newton's Dictionary of Birds. 26. Nest of Oven-bird 187 From Newton's Dictionary of Birds. 27. HoATZiN [Opisthocomus cristatus) 238 From Newton's Dictionary of Birds. 28. Wings of Nestling Hoatzin and Common Fowl, Upper Surface 240 29. Wings of Nestling and Adult Hoatzin, and Nestling of Com- mon Fowl, Upper Surface. (After Pycraft) 241 30. Dissection of Beak-sheath of Cormorant showing Vestiges of Narial Aperture. (After Pycraft) 265 31. Throat of House-sparrow showing the Difference Produced BY Abrasion between the " Winter " and " Summer " Plumages 284 32. Red Game Cockerel 338 By permission of the Editors of The Ibis. 33. Black Polish Cock 339 By permission of the Editors of The Ibis. 34. Types of Combs. (After H. S. Davenport) 340 35. The Sun-Bittern in Display 352 From Newton's Dictionary of Birds. 36. Wing of Arch^opteryx, and Hand of Young Ostrich to show THE Structure of the Wrist 374 LIST OF ILLUSTRATIONS xvii ILLUSTRATION PAGE 37. Wing of a Long-kared Owl showing the Pointeo Type of Wing Associated with Strong Powers of Flight - - - 376 From The Transactions of the Linnean Society. 38. Wing of a " Wood-Owl " showing the Rounded Type. (After Pycraft) - - 377 By permission of the Editors of The Ibis. 39. Shoulder-girdle and Sternum of an Eagle. (After Pycraft) - 379 From The Proceedings 0/ the Zoological Society of London. 40. Shoulder-girdle and Sternum of a Cormorant. (After Pycraft) 381 From The Proceedings of the Zoological Society of London. 41. Shoulder-girdle and Sternum of a Boatswain-bird. (After Pycraft) . . . , _ 382 By permission of the Zoological Society of London. 42. Types of Pelvic Girdles. (After Pycraft) 387 From The Proceedings of the Zoological Society of London. 43. Types of Birds' Feet. (After Pycraft) 395 From The Book of Nature Study. 44. Types of Syrinx 403 45. Forms of the Beak in the Genus Geospiza .... 405 From The Transactions of the Zoological Society of London. 46. Upper Surface of the Wing of a Little Stint to show the Overlap of the Coverts ; and Upper Surface of a Portion OF the Wing of an Owl to show " Diastataxic " Condition. (After Pycraft) 407 From The Transactions of the Norfolk ami Norwich Naturalists' Society. 47. Types of Beaks 413 48. Ear Apertures of the Owls. (After D. Meinertzhagen) - - 416 From The Transactions of the Linnean Society. 49. Skulls of Owls, showing the Asymmetry of the Skull of Tengmalm's Owl, and the Curious Differences in the Form OF the Squamosal in the Young Tawny Owl and Young Burrowing Owl. (After Pycraft) ------- 417 From The Transactions of t lie Linnean Society. 50. Types of Tongues. (After Lucas) 429 LIST OF PLATES The Bittern at Home, a Lesson in Protective Coloration Frontispiece FACING PAGE Powder-down Patches on the Breast of the Heron, Exposed by Pulling aside the Breast Feathers lo By permission of the Editor of British Birds. Wings of Euryl^mus (A) and Colius (B) Dissected to show Deltoideus Muscles ......... 26 By permission of the Zoological Society. Blue-necked Cassowary and the Secretary Bird - - - - 49 Map Showing Zoogeographical Areas, Illustrating the Distribu- tion OF Birds ----------- 63 By permission of Dr. R. Bowdler Sharpe. j Cape Penguins (Speniscus Demersus) ------- 117 From a Photograph by A. R. Momber, Esq. Elephants and Egrets ---------- 124 By permission of Messrs. Rowland Ward, Ltd. From Neumann's Elephant Hunting in Equatorial Africa Bee-Eaters and Bustard 125 By permission of Messrs. Rowland Ward, Ltd. From Neumann's Elephant Hunting in Equatorial Africa. The Peacock in Display 145 From a Photograph by Reid, Wishaw. A Stage in the Display of the Lesser Bird of Paradise - - 147 By permission of the Editors of the Ibis. The Nuptial Dance of the Prairie Hen 149 By permission of the American Museum of Natural History. Black Cock on their Playing-ground 157 From Game-Birds and Shooting Sketches. By permission of the Author. Nest of Remezia 184 From a Specimen in the British Museum. Nests of the Edible Swift 186 From Specimens in the British Museum. xix XX A HISTORY OF BIRDS FACING PAGE Nest of the Herring Gull - - igi From a Photograph by Mr. A. R. Bishop. A Primitive Nest (Nest of the Ringed Plover) . -• - . igi From a Photograph by Major Trevelyan. Emperor Penguin Brooding its Young 216 From a Drawing by Dr. A. E. Wilson. Lapwing Settling Down on its Eggs 225 From a Photograph by the Rev. H. N. Bonar. White-Throat Feeding its Young 225 From a Photograph by Miss E. L. Turner. Meadow Pipit Removing Excreta from its Nest ... - 229 A Breeding Colony of Gannets - - 248 From a Photograph by Messrs. Valentine & Co. A Nesting Colony of the White or Molly-mauk (Diomedea immutabilis) Albatross 249 From The Avifauna of Laysan. By permission of the Hon. Walter Rothschild. Nestlings of Pigeon and Fledgling Barn Owl (from Photographs by Reid, Wishaw), and of Nestling Cape Barren or Cereopsis Goose - 254 From Specimen in the British Museum of Natural History. A Nestling Cas.sowakv and a Nestling Emu 258 From Specimens in the British Museum. Mesoptyle Feathers of Tawny and Barn Owls . - - . 270 By permission of the Editors of British Birds. Shoulder-girdle and Sternum of the Hoatzin .... 313 From Specimens in the British Museum of Natural History. A Factor in the Struggle for Existence (Peregrine) - - - 318 From a drawing by G. E. Lodge. (Falcon Attacking a Rook.) Artificial Selection as Illustrated by Pigeons .... 336 Artificial Selection as Illustrated by Varieties of the Common Fowl (Red Cochin and Brown Leghorn) . - . . . 340 From Photographs by Reid, Wishaw. The Amherst Pheasant in Display 344 From a Painting by G. E. Lodge. The Grasshopper Warbler in Display - 347 From The British Warblers. By permission of the Author. The Kagu in Display 353 From a Photograph in the British Museum. LIST OF ILLUSTRATIONS xxi FACING PAGE The Evolution of the Paddle of the Penguin - . . . 385 After Pycraft. Section of the Head of the Helmet Hornbill, showing the Dense Layer of Horn and Bony Tissue forming the Casque 422 From a Specimen in the British Museum. The Trunk Skeletons of Chionis, the Diving Petrel and the Fork-tailed Petrel ..---..-. 451 From Specimens in the British Museum of Natural History. The Trunk Skeletons of the Guillemot and Diver, showing Modifications Induced by Diving-habits . . . . . ^gj From Specimens in the British Museum of Natural History. Shank of the Leg of the Red-throated Diver and of the Great Crested Grebe . . 452 From Specimens in the British Museum of Natural History, INTRODUCTION LIVING things form an inexhaustible field of in- terest and delight to Man, who is the outcome of an age-long process which has culminated in the production of the human mind with its unique powers of thought. This process has left, as it were, on the way to man, all the varied crowd of lower animals and plants which still survive to tell him whence he has come, and to enable him to arrive at an understand- ings of the secrets of his own nature. No wonder that natural history, the knowledge of animals, plants and stones, has from the earliest times been a serious pursuit, and perhaps we ought not to be astonished when the intimate and deep-seated relations of man with other livinof thinofs is borne in mind, that the most fantastic beliefs about natural history have been current, and that it took a longer time to enable men to investigate animals without prejudice and the domination of childish and preposterous imaginings than it did to start a reasonable examination of less elusive and exciting things, such as plants and the non-living objects of which our senses give us cognisance. The study of animals can never lose its special hold on the human mind, due to the animal's direct appeal to man, its saying, as it were, " You are one of us, you know. We are close to you — ^very close to you : if you can understand my nature, my mechanism and xxiv A HISTORY OF BIRDS origin — snail, robin, squirrel, whichever I am — you will be near to understanding man's nature, mechanism and origin — near to understanding — yourself!'' And so there are endless books on the natural history of animals, their kinds, their structure, their mode of action, their habits, growth, reproduction, food, their relations to one another and to other living things. Any one book treating of animals in every possible way would be too large ; moreover, our knowledge about animals is always growing and receiving quite new accessions, so that no one should complain of the number of such books, and every new one, if it is really a new one and written by a real *' Knower " of animals, should be welcome. Mr. Pycraft's series of four volumes called Animal Life is a really new book on animals, and its novelty and excellence is exhibited in the volume on Birds written by Mr. Pycraft himself. In the first place, let me say what may not be known to every reader, though well-known to all scientific zoologists — that Mr. Pycraft is a most competent authority on birds ; he has devoted his life to them, and has studied with specially favourable opportunities their skeletons and their plumage and the stages in their growth, so as to add greatly to our knowledge. From the museum at Leicester he came to assist me in the University Museum at Oxford in 1892, and later was appointed to the staff of the Zoological Department of the British Museum, where I again had the oppor- tunity of seeing and appreciating his work. In the second place, the plan of the book on Birds (which will be followed in the other volumes on Mam- mals, on Reptiles, Amphibia and Fishes and on Inverte- brates) is original. We do not start with a scheme of classification and then take up the groups one by one INTRODUCTION xxv and examine the different kinds included in each, but boldly, after an introduction on the general structure of birds, the phylogeny of birds is discussed, that is to say, their genetic relationship to the reptiles and the evidences thereof, and a " family tree" showing- the main lines of the descent of birds and the relationships to one another of the numerous groups of birds is given. Then we have a chapter on Geographical Distribution followed by others on the Seasonal Life of Birds, on Migration, on Peculiar Interrelations (such as those of the Cuckoos), on the Relations of the Sexes (including courting, display, fighting, song and music). Then we come to chapters on Nidification, Eggs, Care of Off- spring, Nestling Birds and what they teach (a subject greatly studied by Mr. Pycraft), the Life-history of Birds, Variation, Natural Selection and Artificial Selec- tion in the case of Birds, Sexual Selection, Adaptations and Convergence of form in distinct groups (the latter better called " homoplasy "). These and similar topics are discussed by Mr. Pycraft at greater length than would be possible in a systematic treatise on birds ot the usual scope. ^ The survey of bird-life thus given is a very complete one, and many interesting features of it, liable to be too briefly treated in a book arranged on classi- ficatory lines, are here duly dealt with. The illustrations are of great value, for they are not old but new, and they are admirably executed. I may cite here a few of the more interesting views which Mr. Pycraft advances in the present volume. In regard to the subject of migration (see page 89), he has promulgated one or two new ideas. He holds that the trend of migration is, throughout the world, due north and south, as far as physical conditions render this possible. It appears as a consequence of this that xxvi A HISTORY OF BIRDS our Swallows (for example) do 7iot, as is supposed, on reaching Africa disperse some to West Africa as far south as the Gold Coast whilst others continue down the East Coast to the Cape. But that, on the contrary, our British birds, and those of France and Spain, go to West Africa only. Those that are found along the East Coast of that continent are birds which have been bred in Eastern Europe. It is significant in this con- nection that the Swallows of Northern Asia go south to India and Burma, those of North America to South Brazil. Our British migrants are held by Mr, Pycraft to be so many " local " races of their species. Hence, he be- lieves, has come about the extinction of many of our '* British " birds — Avocets, Spoonbills, Ospreys, Ruffs, Bitterns, etc. As the parent stock is killed down, here and abroad, no descendants are left to return to the old haunts, for the Avocets, Spoonbills, Storks, etc., of the Continent are similarly so many " local " races, having no "inherent knowledge" (if one may use the term) of land outside their particular routes. That migration was and is possible only to such species as can obtain a livelihood outside their place of origin is very justly asserted by our author. Hornbills, Toucans, Birds of Paradise cannot migrate : outside their home- range they would starve. Hence when the areas they inhabit become over-stocked the surplus must perish. Those birds more fortunate, because less specialised in the matter of food, which find salvation in migration, were driven back periodically to the land of their origin by climatic conditions. Having, however, extended their range and hence their breeding area, they returned in greater numbers than those which departed. Hence the land of origin was less able than before to support INTRODUCTION xxvii the returning host, and hence migration became a fixed and necessary habit. The range and increased breed- ing area increased in waves mechanically. The exodus would naturally be to the new-found land of plenty. The birds of last year would return to their old breed- ing station : their young also. But these would be driven by the old birds further a-field and establish new colonies ; for it is well known that birds will drive away their young and jealously defend their appropriated breeding territory against all-comers. Mr. Pycraft makes a laudable attempt to combat the contention, which has been and still is urged, to the effect that small variations in animal colour and form can have no value as features for selection in the struggle for existence. He urges that even if this be true in many cases, yet such small variations will not be sup- pressed by selection adverse to them. They are free to take their course unless and until of such magnitude as to be either checked by natural selection or favoured by it. In illustration of his contention, he cites various facts in regard to the evolution of the skull and ot par- ticular skull bones and other skeletal structures in birds. This view appears to me to be well worthy of con- sideration. In regard to the theory of sexual selection the original views of Darwin and those of Wallace are cited as well as the more serious criticisms of these views advanced by other observers. In the light of some recent work, Mr. Pycraft is led to hold that some slight re-setting of Darwin's views in their application to birds is necessary. Without endorsing his view of the absence of selective action in certain cases, I may draw the reader's attention to his argument. Since it is now known that birds of the most sober hues affect displays of a character in- xxviii A HISTORY OF BIRDS distinguishable from those of birds in which such displays are made apparently for the sole purpose of exhibiting to the best advantage some specially modified or beauti- fully coloured patterns, it seems (our author contends) probable that such resplendent dress is to be regarded rather as a by-product of sexual selection — as a varia- tion allowed to assume a moi'e ^r less extravagant form because unchecked by natural selection. That display is the result of sexual selection is not doubted by Mr. Pycraft, for even the most incon- spicuously coloured birds indulge in antics, more or less grotesque, when dominated by sexual desire. Any varia- tion in the direction of more resplendent plumage would thus of course be free to fulfil its potentiality unless, and until, checked by natural, selection. The view advanced by Mr. Pycraft is in short this — that the " display " is older than the resplendent plumage, and is not the consequence of its presence. Sexual selection is still regarded as operative, for there must have been degrees of splendour among the ancestors of the now resplendent species, and the brighter coloured would excite the females more effectively. Mr. Pycraft considers at some length the coloration of desert-dwelling forms of birds. He emphasises the contention that natural selection is not the aofent which has in the first instance determined that coloration. I confess that I should not have supposed that any one would contend that it has done so, any more than that the view could be supported that " natural selection " has primarily started any of the variations of colour or form upon which it operates. Mr. Pycraft holds that there can be no question but that the peculiar physical conditions of a desert environment exercise a direct influence on pigmentation. It is very possible that INTRODUCTION xxix such a direct effect of one kind or another is in many instances produced. But in all such matters one would like to see experimental proof and to have full chemical explanation of the details of the coloration and the way in which external conditions directly modify it. Mr. Pycraft thinks that a humid atmosphere undoubtedly causes an intensification of pigment inclining to melan- ism. That would be very important if it were experi- mentally demonstrated, but that seems not to be the case, nor is the chemical change by which such intensi- fication of pigment, or the production of independent black pigment, could be arrived at by the action of a humid atmosphere as yet suggested. Our author says that of course natural selection " may have " acted by securinor elimination of all those individuals which were not physiologically affected by desert conditions, viz., intense light and heat, or (I should be inclined to add) were not, owing- to other causes, variations in the direction of sand-colour. In regard to the life-history of birds, Mr. Pycraft has drawn attention to a host of facts which have hitherto been ignored by leading Darwinians, though of first-rate importance from their point of view. Such are his own observations as to the coloration of nestlings and of immature birds showing the significance of striped nestlings and of the brilliantly coloured mouths of certain species. He gives very cogent reasons for regarding the ancestral bird as arboreal, and as gradually acquiring flight by "parachuting". The view that the earliest birds were aquatic and that the wing was at one time a paddle is, however, still capable of defence. To arrive at anything like a preference between the two theories requires a very extensive survey of anatomical and palseontological facts, as well as a consideration of the XXX A HISTORY OF BIRDS various mechanisms of flight in animals and their rela- tion to other locomotor organs. It is distinctly a feature of Mr. Pycraft's book that he has given a larger number of illustrative examples of adaptation to environment, of homoplasy and parallelism, than is to be found in any other book on birds. E. RAY LANKESTER LIST OF AUTxHORS QUOTED Alcock, Dr., ii6. Alexander, Capt. Boyd, 82. Allen, J. A., S3, 85, 292. Andrews, Dr. C, 112, 150, 290. Barrington, R. M., 294. Bates, 423. Beebe, C. W., 81, 315. Beddard, F. E., 47. Bonhote, J. L., 272. Bumpus, Dr., 293. Butler, A. G., 234. Chapman, A., 326. Chapman, F. M., 95. Clarke, Eagle, 96. Cunningham, J. G., 315. Darwin, C, 321, 335,337, 411. Davidson, W. K., 146. De Varigny, 346. Dwight, Dr. J., 281. Elliott, Dr. D. G., 172. FiELDEN, Col., 298, Finn, F., 328. Forbes, H. O., in. Furbringer, Prof. Max, 47. Gadow, Dr. H., 47, 251, 310, 312. Gatke, 96, 97. Giglioli, Prof., 303. Godman, Dr. F. D., 225. Grant, Ogilvie, 147, 305. Giinther, Dr. A. L., 232. Harvie-Brown, J. A., 298. Headley, F. W., 281, Howard, H. E., 290, 347, 348, 351. Hudson, W. H., 114, 163, 323. Jordan, 251. Kellogg, 251. Kerner, A., 107, in. Lankester, Sir Ray, 342, 453. Latter, O., 130. Lucas, F. A., 122, 431. Millais, J. G., 157, 345. Mitchell, Dr. Chalmers, 410, 437. Moseley, Prof., 449. Murie, Dr., 149. Nelson, E. W., 162. Neumann, A., 125. Newbigin, 199, 310. Newton, Prof., 90, 103, 119, 136, 180, 285, 301. Nicoll, M. J., 117. Nutting, H., 162. Osborn, Dr. H. F., 453. Palmen, Prof., 94. Poulton, Prof. W. B., 323, 327. Pycraft, W. P., 410. Ridley, H. N., no. Romanes, G., 355, 356, 357. Rothschild, Hon. W., 162, 308, 309. Saunders, H., 120, 297, 298, 301. Sclater, Dr. P. L., 76. Seth-Smith, D., 171. Sharpe, R. B., 92, loi, 102, 363, 443. Sorby, Dr., 198. Tennant, S., 95. Ussher, R., 87. Vernon, H. M., 318. Von Rosenberg, Dr., 218. Waldo, Meade, 225, 285. Wallace, A. R., 100, 147, 193, 208, 329, 330- Warren, R., 345. Whitaker, J. S.. 81, 86, 90. Wilson, Dr. A. E., 216, 217, 287, 320, 432. A HISTORY OF BIRDS CHAPTER I INTRODUCTORY General characters of structure — feathers, glands, the skeleton, the respira- tory system, the lungs and air-sacs, the digestive system, the circulatory system, the muscular system, the nervous system, the senses. nr Birds, in Broad Outline HOUGH the bird and the mammal are ahke descend- ■ ants of the scaly reptile, they present no points in common, save that both are " warm-blooded ". Birds are essentially creatures of the air, mammals of the earth : yet, be it noted, some birds have lost the power of flight, while some mammals, in varying degrees, have acquired this ; albeit only one group, the bats, have really mastered the art. Birds, in short, from the first were destined by Nature to possess the air, while mammals were, on the other hand, de- veloped along lines which made the earth their natural abiding place. And this fundamental difference explains the fact that, structurally, the birds present a remarkable degree of uniform- ity, while the mammals, on the other hand, display a wonderful diversity of form and structure. The mechanical requirements of flight rendered this structural uniformity inevitable ; while, on the other hand, the terrestrial life of the mammals left open a wide range of variability in the matter of bodily shape, and this in time manifested itself, as the need arose, as, in the struggle for existence, some took to climbing trees, some to burrowing in the earth, some to the rivers, and some to the open sea, some to the burning deserts, and some to the wild fast- nesses of the sombre mountains. 2 A HISTORY OF BIRDS By the accident of birth, so to speak, the career of the bird was determined by the shape of its fore-h'mbs. Though in course of time circumstances deprived these of all importance in certain species, so that they eventually became reduced to mere vestiges, as in many living birds, or even suppressed en- tirely as in the extinct Moas, the mammals, on the other hand, have in no case suffered a similar loss ; but the hind-limbs, by way of contrast, have in not a few cases similarly vanished. In birds the fore-limb has in all cases served as an organ of flight; even where this member has been reduced to the merest vestige, it is clear that the modelling thereof is that of a wing. In the mammal, on the other hand, the fore-limb presents the most varied forms. Similarly, in the case of the hind-limb, that of the bird presents a wonderful uniformity of structure, being always used for the carriage of the body when on terra- firma, but this is far from true of the mammal. Notwithstanding the unquestionable uniformity of structure which birds present, this is apparent only when the fundamental structure is considered in relation to that of other groups. To the ornithologist birds display a marvellous range of variation, and in so far as coloration is concerned this is undoubtedly true. From the aesthetic point of view birds hold an unique position, and fill a place in the world that adds more than is generally realised to its charm and habitability. They seem to display a joyousness in existence, an intensity of emotion, that is infectious ; though, it is needless to remark, this mani- festation is not a universal characteristic of the group. The factor which, more than any other, has secured for birds the high place which they hold in the affections of men, is unquestionably that of flight. Thereby they ever keep themselves, as it were, before the public, and give life and beauty to the world around them. And this is true more especially of such species as seek their daily bread in the open, on the wing, or indulge in ferial evolutions apparently out of the sheer ex- uberance of spirit. There must be few who have not gazed with admiration at the hovering feats of the Kestrel, and still fewer who have not felt moved at the wild, screaming flights of a flock of Swifts at dusk, while the marvellous spiral evolutions of the Skylark, accompanied by outpourings of song, have in- spired '^ome of the finest poets who have ever lived. INTRODUCTORY 3 The vivid hues which so many species display must be reckoned as only slightly less important in this respect than flight. This fatal gift of beauty has from earliest times sub- jected the wearers to a rigorous persecution, not only at the hands of savage races, but of peoples boasting themselves civilised, among whom women have always been the worst and most heartless offenders. On account of the ceaseless persecution to which these defenceless creatures have been subjected to meet the demands of fashion, savage and " civil- ised," many species have become wiped out of existence, and of many more the doom is sealed ; the more beautiful of the Birds of Paradise and of the Humming-birds, for example, will, in another decade, have ceased to exist ! There is more in this colouring of the plumage than meets the eye of the unobservant ; for whether we contemplate broad bands of vivid colours, sharply defined ; or intricate patterns, fine as the most delicate lace work, we are confronted with a mystery which is so far insoluble — what determines the seg- regation and deposition of these pigments? The problem presents its greatest difficulties in such feathers as display, individually, intricate patterns, whether of sober shades or hues such as vie with, or even surpass, the rainbow in splendour. Take, for example, a feather displaying a series of fine concentric lines, divided by wider bands of white, or black, or red, as the case may be. These lines are not continuous, not organically complete, but formed by the exact relation, one to another, of a series of minute spots of pigment, each lodged in a separate filament, so that the several spots in each separate filament, when ranged side by side, form the several series of lines, straight or vermiculated, as the case may be. All that we can say is, that the spots in question are deposited simultaneously in each rod as the feather grows. But what controls the alterna- tions of the deposition of the pigment necessary to bring about so simple a pattern as that to which we refer? And what determines the changes of pattern in the different areas of the body? But birds have yet other attractions for us men. Graceful in their movements, and exquisite in their apparel, they are furthermore fascinating in their lives, for they display in their periods of courtship a singular vivacity, and in the care of their offspring a marvellous tenderness and solicitude. 4 A HISTORY OF BIRDS There is, in short, no single phase of their Hfe-history which is not throbbing with interest. Nests, eggs, and young, ado- lescent and adult, at rest or in action, there is no phase which is not overflowing with matter for reflection, no single incident which is dull ; and this is perhaps more than can be said for any other group of animals. Birds, like mammals, display a wonderful plasticity to environment. There is no spot on the earth's surface which has not been made to provide a habitation for them, from the icy and storm-swept regions of the poles, to the equator : while by relatively slight structural changes, they have contrived to avail themselves of food supplies of the most varied description. The general homogeneity which birds present, when com- pared with the mammals, or the reptiles, is generally attri- buted to the fact that they are less ancient than either : though they may yet claim a respectable antiquity, since the earliest known bird dates from the Jurassic epoch. It is supposed by some that enormous periods of time are necessary to bring about the extinction of connecting-links, and the con- sequent formation of sharply defined groups, such as are to be met with among the mammalia. But it may well be that this work of extermination among the birds has been largely evaded, and homogeneity preserved, by their ability to escape from unfavourable conditions. With the mammals the avoidance of periods of stress, of whatever kind, has always been restricted. Migration has been limited by unsurmountable barriers ; at one time mountain ranges, at another of vast stretches of water. To this evasion of Fate most modern taxonomers owe their difficulties in their attempts to classify birds, that is to say, those who desire merely to establish so many well-defined groups which can be readily summarised in the form of a " Key ". Those, on the other hand, who have spent laborious days in the endeavour to trace the descent of the more or less well-marked groups of living and extinct birds, though hardly more successful than their less ambitious neighbours, must look to yet other and more subtle factors. First, and foremost, must be placed the fundamental modification due to the ex- igencies of flight, which all birds, without exception, share in common. Thereby the range of possible variation has been kept within very narrow limits, and secondly, there must be INTRODUCTORY 5 reckoned the phenomena of convergence and parallel develop- ment. In taking a bird's-eye group of the Class Aves one may dis- tinguish a number of apparently well-defined groups, such as the Ostrich tribe, Diving-birds, Penguins, Petrels, Steganopodous- birds, e.g., Gannets and Cormorants, the Goose tribe, Storks, Birds of Prey, " Game-birds," Cranes, and the Limicolae or "Shore-birds": and against these may be set the Parrots, Cuckoos, a host of forms commonly known as " Picarians," including, for example, the gorgeously coloured Rollers, King- fishers and Bee-eaters, and the bizarre Hornbills, the Owls and Night-jars, the Swifts, and the jewel-like Humming-birds, the gaudy Toucans, and the Woodpeckers. P'inally, we have the most puzzling of all, the " Passerines," of which the crows may be taken as typical examples. So far, any classification of this medley of forms, which shall express the lines of descent, has proved beyond attain- ment, though much towards this end has been done by the labours of such men as Huxley, Garrod, Forbes, Fiirbringer, Gadow, Beddard and Chalmers Mitchell. General Characters of Structure The Feathers For the purposes of these pages a very general survey of the structural characters of birds will suffice. And this survey cannot well begin better than with a general account of the feathers, since these, as we have already remarked, are unique structures. In their nature they answer to the scales of Reptiles rather than to the hairs of Mammals. In addition to those which form the outer covering of the body, and hence are known as the " contour " feathers, there are several other forms of feathers. The most familiar of these are the "down feathers" which play so important a part in commerce. These form, in many birds, such as the Goose tribe. Gulls, and aquatic birds generally, a dense underclothing answering to the under-fur of mammals, such as, for instance, the " fur-seal," and after these come the " filo-plumes " and " powder-down " feathers to be described presently. A HISTORY OF BIRDS A typical contour feather consists of a central axis, and a vane or vexillum. The axis is divisible into two portions : (a) III. I. — Diagrams Illustrating the Structure of a Feather I. A contour feather showing the calamus or quill (C), the rhachis or shaft (R), and the web or vane (V) attached thereto. On the right-hand side of the vane is a portion showing the appearance presented under a low magnifying power, B = barb and Bs = barbule. II. A section cut across two barbs parallel with the barbules of the anterior series to show the method of interlocking. III. Shows a barbule of the anterior series (A) with its booklets, and two barbules of the posterior series (B). a hollow " calamus," and {/3) a .solid rhachis or shaft. The calamus forms the lower portion of the axis and is inserted by its base INTRODUCTORY 7 into the skin. Tubular in shape and semi-transparent, it en- closes a series of hollow, oblong cells fitting one into the other. During the growth of the feathers these cells contained the pulp, or nutrient matter out of which the feather is built up. The shrivelled end of the last of these cells projects from a small aperture — the upper umbilicus — at the point where the quill passes into the " rhachis " or shaft. This is formed by a process of continuous growth of the dorsal surface of the calamus, and the resultant lateral edges of this projecting out- growth ultimately curl inwards, meeting in the middle line of the under surface of the feather and leaving a fine groove to mark the junction. The enclosed cavity is simultaneously filled with a closely packed mass of " pith "-cells, recalling " elder-pith," giving stability and elasticity to this region of the axis. Along each side of this rhachis, which has a quadrangular section, there runs, from the region of the upper umbilicus to the tip of the feather, a closely planted series of flattened laminae, terminating in a point, and these in turn support a double row of smaller laminae. The former are known as the rami or " barbs," the latter as the " radii " or barbules. The whole form the remarkably elastic fringe which runs along each side of the shaft, and which together form the " vane " or " vexillum " of the feather. This fringe must be more closely examined. On a super- ficial inspection it presents a homogeneous surface, but grooved withal by a number of fine, parallel lines. If an attempt be made to stretch this web in the direction of the long axis of the feather, it will be found that though at first resisting, it will eventually split, when, by drawing the fringe through the fingers the original unity will be restored. If a lens be now brought to bear on this surface, it will be found that the grooved or ribbed appearance of this vane is caused by the interspaces between the rami just described ; interspaces which are more or less perfectly filled by the series of barbules which intercross. Under a high magnification of the microscope these barbules will be found to consist of two very distinct kinds, ranged one on either side of the barb. Those on the side of the barb pointing to the tip of the feather have the appearance^ — ^when examined separately — of flattened plates, cut up, from the middle out- wards, into a number of long, hooked filaments, while those 8 A HISTORY OF BIRDS of the opposite side of the barb take the shape of long scrolls, whereof the upper edge is the more deeply curled. When in situ the two series are so arranged that the booklets are thrust down between the scrolls so that their curled edges are caught thereby. A reference to the accompanying diagrams will make these points clear. The number of these rami or barbs I II A ?Q^ III. 2. — Contour Feathers showing the Hyporhachis or After-shaft (A) I. Of a Pheasant. II. Of an Emu. depends mainly on the length of the feather. Along the inner web of a Crane's quill feather 38 cm. long, Dr. Hans Gadovv counted about 650 rami : he further estimated that every ramus of this feather bore about 600 pairs of radii (barbules), mak- ing nearly 800,000 radii for the inner web alone, and more than a million for the whole feather. The contour feathers of most birds bear what is known INTRODUCTORY 9 as an aftershaft (hyporhachis). This is a duplicaturc of the main shaft, but much smaller and more delicate, and springs from the upper umbilicus of the main shaft. In the Game- birds it is especially well developed, while in others it is reduced to a mere vestige, or is wanting altogether. In the great feathers which form the "quill" or "flight" feathers {remiges) of the wing, and in the tail feathers {rectrices) the after shaft is invariably wanting. Among the Ostrich tribe it is present only in the Emus and Cassowaries, and here it is of great size, as large indeed as the main shaft. The contour feathers of the Ostrich tribe — save only in the Tinamous — it may be remarked, are peculiar in that their vanes are not held together to form a well-knit " web," the radii being degenerate, and failing to hold the vanes together ; hence these vanes are said to be "discontinuous". Down feathers differ from contour feathers in that the barbs, or rami, of the feathers are of great length and slenderness, and often all arise from a common base — the top of the calamus, instead of being ranged along each side of a long rhachis. The radii (barbules) of such feathers are represented by mere filaments, or sometimes by nodular swellings, which again may assume a pyramidal form. As touching "filo-plumes" little is known' as to their mean- ing or purpose. There are the long hair-like threads which remain sparsely distributed over the body of a fowl when plucked. They grow in clusters of five or six, or more, about the bases of the contour feathers, and when examined micro- scopically are found to consist of a simple, solid axis, terminating in a few weak barbs and barbules. An examination of the late stages of growth, just before development is complete, however, shows that these are degenerate feathers, inasmuch as there will then be found a considerable number of barbs, arranged much after the fashion of the barbs of a down feather. Among these one will be found stronger than the rest, and this eventually is left, the rest disappearing. In some birds these filo-plumes play a conspicuous part in the coloration of the surface of the body, since in such cases they attain a great length, and develop relatively large vanes. These project beyond the level of the contour feathers and may form large white patches, as in the thigh patches of the Cormorants, or lO A HISTORY OF BIRDS they may give a hoary appearance to the necks of these birds. In some other birds the filo-plumes are distributed as conspicu- ous hair-Hke threads all over the neck and back, e.g., the genus Criniger. The rictal bristles of Night-jars and Fly- catchers, and the eye- lashes of many birds, e.g.., Ostriches and Hornbills, appear to be akin to filo-plumes. The significance of powder-down feathers is still more puzzling. These are most per- fectly developed in the members of the Heron tribe, where they form large patches over the breast or thighs. But they occur also in many other birds, not- ably in Parrots and some birds of prey, and in the " Frogmouth " T, A TA T^ (Podargus). "Among 111. 3. — A Developing Filo-plume showing d • u • THE Rami which later disappear, and the the Passerme birds Main Shaft (f) which remains to form the fj^gy a.re met with onlv " FiLo-PLtiMF. " y y in the " Wood-Swal- lows" (^Artamns). In the Parrots and Hawks they occur only as sparsely dis- tributed tufts, in other cases in the form of large patches. When examined these feathers are found to consist of a number of barbs matted together, and of an exceedingly friable char- acter, so much so, that they are continually disintegrating into a fine powder which to the touch resembles '• fuller 's-ear th ". The curious bloom, which covers the beak and face of the African Parrot {Psittacns eritJiaais) and the plumage and beak of Cockatoos, is due to this powder. There is a tradition — quite unfounded — to the effect that in the Heron tribe this ' filo-plume ' p = pith-cells. T = transient rami. POWDER-DOWN PA-I'CHKS ON THE BREAST OF THE HERON, EXPOSED i;V PUI.l.INO ASIDE THE BREAST FEATH EKS INTRODUCTORY ii {)owder-do\vn is luminous, and that the birds take advantage of this kiminosity by raising the contour feathers so as to shed this Hght on the water wherein they may be fish'ng, and thereby lure their prey to within striking distance. As these birds do not fish by night, and the glow would be invisible by day, this theory may be regarded as exploded. The feathers of nestling birds do not differ structurally from those of adults in any essential particular, but they are remark- able for the very great range of degeneration which they dis- play. On the varying number of successive plumages through which nestlings pass before attaining to a dress which is structur- ally equivalent to that of the adult much will be said later. The nestling down feathers, it should be remarked, are known as "neossoptyles" to distinguish them from the " tele- optyles," or adult feathers — terms coined by Dr. Hans Gadow to serve a most useful purpose. The neossoptyles are made up (a) of feathers which im- mediately precede the contour feathers of the adult ; and (/3) of feathers which are later succeeded by down feathers. The former are to be known as " pre-pennae," the latter as " pre- plumulae ". The pre-pennae may further be divided into " protoptyles " and " mesoptyles " ; and while the nestlings of some species develop both, in others the protoptyles have become suppressed, while the mesoptyles are degenerate, and may be represented by little more than a few straggling, hair-like filaments, as in young Pigeons, or the nestling may remain absolutely naked until the appearance of the first " teleoptyles ". Only in some species of Tinamous are the mesoptyles really well developed, and here they very closely approach teleoptyles in structure, but are peculiar in that the after shaft is almost as large as the main shaft, a point wherein they agree with the teleoptyles of the Emu and Cassowary. This is a very remarkable and puzzling fact, because in the adult Tinamou the after-shaft is either feebly developed or wanting, and in the nestlings of the Emu and Cassowary, and the Ostrich tribe in general, the after-shaft is degenerate, or absent ! In the nestlings of certain Owls, i\^o-., Tawny and Eagle Owls, the mcsoptyle plumage is worn until the first autumn, at least in so far as the trunk feathers are concerned, for the quill and tail 12 A HISTORY OF BIRDS feathers are of the true teleoptyle type before the birds leave the nest. These mesoptyles are, in such species, preceded by a pecuHarly downy plumage made up of the protoptyle feathers. In the young Barn Owl the protoptyles are never developed, while the mesoptyles have so far degenerated as to be indis- tinguishable from protoptyles. That they are really mes- optyles is shown by the fact that, like all mesoptyles, they are thrust out upon the tips of the teleoptyles as soon as these develop (p. 271). In some birds, as in nestling Game-birds and Owls, pre- pennai only are developed. In others, as in nestling Hawks, the pre-plumute are larger, and play a more important part than the pre-pennae. And from this there is but a step to the suppression of the pre-pennae altogether, as in the young of the Cormorant, wherein the nestling is clad only in pre-plumulae. I II f,6.s^. III. 4. — Pterylosis of Acanihidositia cliloris showing the Feather Tracts Pt. cap. = Pteryla capitis. Ft. h. ^ Ptcryla Iiiuitcralis. Pt. sp. = Pteryla spinalis. Pt. f. — Ptcryla fciuoralis. Pt. coll. v. = Ptcryla colli vcntralis. Pt. V. = Ptcryla vcntralis. (By permission of the Editors of T/ic Ibis.) The feathers of birds are not evenly distributed over the body, as are the hairs of, say, the horse, but are gathered to- gether to form more or less sharply defined tracts (pterylae), leaving large bare spaces or " apteria," though in many birds such apteria are covered with down feathers. The nature of these tracts may be seen in 111. 4. Since they assume char- INTRODUCTORY 13 acteristic forms in different groups of birds they are of value for taxonomic purposes. The feathers on the wings of birds have a quite pecuh'ar arrangement, and this is true more especially of the great " flight " feathers or quills. These are arranged along the upper surface of the skeleton of the fore-arm and hand, being 14 A HISTORY OF BIRDS fairly well spaced on the former, crowded together at their bases on the latter (111. 5). The quills of the fore-arm, or " secondaries," vary in number according to its length, never falling below six or exceeding thirty-seven. But the quills of the hand — the " primaries " — never exceed twelve in number among Neognathine birds, and never fall below ten, though the tenth may be reduced to a mere vestige, known as a " remicle ". The bases of these "quills," and the surface of the arm generally, are covered by feathers arranged in definite order. These are known as the coverts, whereof four distinct groups are distinguished. The first of these are the major coverts. These are always large and strong feathers, and are closely attached to the bases of the quill feathers ; the next row are known as the median coverts ; beyond these run from one to five rows of minor coverts, while beyond these come the marginal coverts. The same rows are represented on the under surface of the wing. Since these coverts present characteristic features in each of the great groups of birds, they are useful for taxonomic pur- poses ; and this is more especially true of the manner in which those of the upper surface overlap one another. Thus, the major coverts always lie with their free edges turned towards the tip of the outstretched wing, and so also, very commonly, do the median series. The overlap is then said to be " distal ". But the outermost median and minor coverts frequently have an opposite, or proximal ov-erlap, that is to say, the free edges of the feathers face towards the body. The marginal coverts always overlap distally. But the details of this matter should be sought for in the special treatises on this subject rather than in these pages. While it seems impossible to discover any significance in the matter of this overlap in the smaller coverts, this is by no means the case with the great flight feathers and their coverts. With a distal overlap, as the broad surface of the wing is raised during the up-stroke in flight, the resistance of the air is reduced to a minimum, since it forces down the inner webs of these feathers and so escapes ; but during the down-stroke, this re- sistance forces these inner webs upwards, driving one against another, and so forming a continuous, unyielding surface, as perfect as that afforded by the membrane of the wing of the bat. INTRODUCTORY 15 Where the arm (humerus) is long, as for example in the Alba- tross, the gap between the innermost quills of the fore-arm and the body, which would be formed during flight, is filled up by a series of long feathers which are related to the humerus much as are the secondaries to the fore-arm. But with this difference, in the arm this series is double, one running along the upper, and one along the under surface of the shaft. But for this bridging, flight would be impossible. Glands Birds have no sweat glands. Indeed the only skin gland they possess is that known as the Oil-gland or Uropygium, which is situated above the bases of the tail feathers, and secretes a fairly abundant quantity of clear oil. In some birds this gland ends in a pointed nipple, e.g., Owls; in others it bears a tuft of feathers, e.g., Ducks. As to the use of this gland : it may be remarked that it is now universally believed to serve as a reservoir for the secretion of oil which is used by the bird for the purpose of dressing the feathers. It is supposed to be applied by the beak, the bird turning the head backwards, and gently squeezing the nipple of the gland. The oil thus expressed is then applied to the feathers, individually, by drawing them through the mandibles, and thereby it is believed aquatic birds make their plumage waterproof. So deeply rooted is this belief, that he who would nowa- days presume to question its truth would be branded as a heretic, or worse. The late Charles Waterton had the temerity to cast doubt upon this hypothesis, and was promptly scorned for his pains; nevertheless, there are grave doubts as to the function of this gland. And these can be briefly set forth by one or two striking cases. To be of any use as a lubricant this oil must be very skilfully applied : yet there are many birds wherein this gland is well developed which could not possibly take up and spread so much as one drop of this precious fluid. The Scissor-bill is perhaps the most striking instance of this, for in this bird the lower is not only longer than the upper jaw, but both jaws, from the gape of the mouth onwards, are compressed to form a single blade as flat as a paper-knife. The Pelican is tongueless, and i6 A HISTORY OF BIRDS has a long unwieldy beak : how could this seize upon and distribute oil over individual feathers drop by drop ? Simil- arly, the Shoveller Duck and the Petrels of the Genus Prion have the edges of the jaws fringed by very long, delicate lamellae : how, with such an armature, could drops of oil be expressed from the gland and spread over the feathers : or how could this be done by the serrated beaks of such birds as the " Saw-billed Ducks " and the Darters ? The Anastomus, or Open-bill Stork, and the Whale-headed Stork again, would surely find such a feat impossible. And these, be it noted, are all aquatic birds. On the other hand, the Bustards, many Pigeons and Parrots, and the Ostriches have no gland : yet they keep their feathers in as good condition as those birds which possess this organ. So copiously is this secretion said to be formed in the gland of the Concave-casqued Hornbill {Diclioccros lncornis) that the feathers of the Jieck I are said to be stained yellow thereby ! Nevertheless, ninety-nine out of every hundred Ornitholo- gists are firmly convinced that they //az>e seen the oil squeezed from the gland, and witnessed its application. If, after all, it should be proved that this gland is 7iot used as tradition assures us, what then is its purpose ? So far no really satisfactory hypothesis presents itself. But the same is true of many other glands in other animals. It is possible, however, that it may have served, and may still serve, as a scent gland : though the odour may not be traceable by the olfactory nerves of the human subject, save in one or two cases. In the Hoopoes, for example, it gives forth a most offensiv^e odour, while in the Musk Duck {Bi:::iura lobata) it sends forth a musky smell. The peculiar smell of Petrels is also appar- ently due to the secretions of the oil-gland. TJie Skeleton Birds show their reptilian ancestry in the skeleton more clearly than in any other part of the body, though even here the evidence has been largely masked by the modifications due to flight. The reptilian characters are more conspicuous in the pneumaticity of the bones, the structure of the skull, and the great number of the neck vertebrae, and the structure of the hip- INTRODUCTORY 17 girdle and hind-limb. The shoulder-girdles are unquestionably reptilian, but this is not so patent as are the other characters. While in some birds, as in the Hornbills for instance, every bone in the skeleton contains spacious air-chambers, in others, the long bones at any rate — the bones of the wings and legs — are filled with marrow, and this is true even of such skilled performers on the wing as the Swallows. The peculiar char- acters of the shoulder-girdle, wing, and hind-Hmb will be dis- cussed later in these pages. T]ie Respiratory System The respiratory system of birds presents some points which demand a brief notice. The Lungs In the first place the lungs are not suspended freely within the body cavity, but are closely affixed to the dorsal wall of the anterior portion of the thorax. In the second place they differ from the lungs of other vertebrates in that the respira- tory air is not simply drawn into the lungs and expelled again, but is rather drawn through them and passed into a series of large thin-walled chambers lying along each side of the body cavity, and known as the air-sacs. The air stored in these reservoirs serves not only for respiratory purposes, but also as regulators of the temperature, thereby compensating for the lack of sweat glands. TJie Pulmonary System of Air-sacs There are five pairs of these air-sacs. The first, or cervical pair, lie one on either side of the base of the neck and may give rise to a number of smaller cells which run up the neck, and even into the head ; while small side branches may penetrate between the muscles of the neck, the vertebrae, and the various cranial cavities : or they may form large inflatable sacs in the region of the throat, as in the Prairie-fowl and Frigate-bird. The second pair are known as the interclavicular sacs. In the Ducks they communicate one with another, while in the Storks they combine to form a single chamber. Lateral ex- tensions of these sacs form large axillary chambers ultimately penetrating the humerus and other of the wing bones, the i8 A HISTORY OF BIRDS L Al;.S large pectoral muscles, and the body and keel of the sternum. The third and fourth pair are the " anterior and posterior intermediate sacs," and are enclosed within the thoracic cavity, extending backwards more or less far into the abdominal cavity. The fifth pair form the "abdo- minal sacs ". Of large size, they are continued backwards to the end of the abdominal cavity. This elaborate system of air- chambers is further complicated in many birds by an extensive system of pneumatic cells extending between the muscles, and between the muscles and the skin, so that the bird is abso- lutely encased in a layer of air en- closed between the skin and the body. This emphysematous condi- tion is most perfectly developed in birds such as the Gannets, Screamers and Hornbills. TJie Ncxso-pharyngeal System of A ir-sacs But there is yet another system of air-cells to be mentioned, which is known as the " tympanic " or " naso-pharyngeal system ". While in the majority of birds this is con- cerned merely with the supply of air to the bones of the skull, in the Adjutant Storks it gives rise to a very remarkable pouch which runs down the front of the neck as far as its middle. It can be inflated and deflated at pleasure, communicating as it does with the nasal chamber through an aperture in the floor of the orbit, -pouches of the Great Bustard and the here. That of the first-named forms III. 6. — Dissection Showing THE Lungs and Air-sacs ov A Bird Pb. s. = Pre-bronchial sac. Ax. = Axillary sac bounded ex- ternally by the breast-muscles, seen here in section. S. s. = Partition dividing anterior inter- mediate sac (A.i.s.) from the sub-bronchial sac. P.i.s. = Pos- terior intermediate sac. O.s. = Oblique septum. H.s. = Hori- zontal septum. L. Ab. s. = Left abdominal sac. H. = Heart. G. = Gizzard. L. = Liver. In. = Intestine. (After Strasser.) The extraordinary air Emu may be mentioned INTRODUCTORY 19 a relatively enormous cavity, having extremely thin walls, lying immediately under the skin of the neck, and opening im- mediately under the tongue. Peculiar to the male, it must be regarded as a variation of the pouch described just now in the Adjutant. Only one other bird possesses a similar chamber, and this is the Musk Duck {Biziura lobatd). But here the pouch is very small, and is lodged in a sac depending from the under- side of the lower jaw. The pouch of the Emu is formed by an evagination of the lining membrane of the windpipe, and makes its escape along the ventral aspect of the trachea, near its middle, where the tracheal rings for some distance are cut away, as it were, to permit of the exit of the pouch (p. 401). The pulmonary system of air-sacs make their first appear- ance in the embryo at about the eleventh day, as small vesicles from the surface of the lungs, formed by dilations of branches of the bronchial tubes. As they develop they push the peri- toneal membranes before them. Thus they acquire a two- layered wall — the outer serous layer formed by the peritoneum, the inner by the lining of the bronchial tubes from which they take origin. The Digestive System The digestive system of birds betrays its reptilian origin in many ways, but perhaps most markedly so in the arrange- ment of the annular and longitudinal muscular layers of the intestine, the longitudinal layer lying within the annular, while in the mammals the reverse order obtains, the longitudinal layer, with the serosa, forming the outer wall of the tube. In most birds the food is swallowed without any attempt at mastication, and passed backwards into the oesophagus. As a rule this tube, in the region of the furcula, dilates to form a more or less globular or bi-lobed and thin-walled " crop ". Here, mixed v/ith saliva and water, and warmed by the heat of the body, the food is softened and passed on to the stomach. This again is divisible into two distinct portions, an anterior, the " Proventriculus," with thick glandular walls, and a posterior, the " Ventriculus " or " Gizzard," whereof the walls are thick and muscular, and furnished with a more or less rugous and indurated inner surface. In grain-eating birds the inner walls of the gizzard are furnished with a pair of apposed and greatly 20 A HISTORY OF BIRDS thickened pads, which, by means of spirally arranged muscular fibres, are made to rub together in opposite directions after the fashion of a pair of millstones. But this work of trituration is further aided by a mass of small stones swallowed, and retained by the gizzard, for this purpose. In the pigeons of the genus Ptilopus there are four such pads, so that the gizzard is cross- shaped in section. In fish and flesh-eating, and in insectiv- orous and fruit-eating birds, the gizzard is feebly developed, the proventriculus and ventriculus passing insensibly the one into the other. The latter, in fish-eating birds, such as the Herons and Cormorants, may assume the form of a long oval sac extending along the whole length of the abdominal cavity ; while, by way of contrast, it should be mentioned that in other piscivorous forms, such as the Tropic-birds, Pelicans and Gannets, the gizzard or ventriculus is much reduced, the pro- ventriculus being in consequence of considerable size. In the Cassowaries and Emus and in Tanagers of the genus Euphones similar relations obtain between these two portions of the stomach ; but in the Hoatzin, which has also a greatly reduced ventriculus, it is the crop which has become enlarged (p. 313). The inner lining of the stomach is naturally constantly wearing away and being reproduced, but in some birds this lining is suddenly cast off and ejected through the mouth as in the Starling, Missel Thrush, Little Owl, Cuckoo and Horn- bill. The Cuckoo and Trogons of the genus Harpactes are further peculiar in that the inner lining of the gizzard becomes beset with hairs, spirally arranged, derived from the caterpillars on which these birds feed. In birds of prey the fur and feathers of the victim swallowed, and in some grain-eating birds the husks, are formed into " pellets " and ejected through the mouth. The intestines, with the external digestive glands — the liver and pancreas — attached thereto demand little notice here. Suffice it to say that three portions thereof may be distinguished - — the duodenum^ a closed loop embracing the pancreas, and re- ceiving the hepatic and gall-ducts ; the ilcmn or " small in- testines," the longest portion of the gut, and the recttini. The last-named is shut off from the ileum by a special valve, the "ileo-csecal," which, while it permits of the contents of the gut passing into the rectum, hinders any return thereof. INTRODUCTORY 21 The convolutions into which the small intestine is thrown, for the purpose of securing a greater length of gut, and con- sequent increased digestive surface, are of considerable value for taxonomic purposes, as Dr. Hans Gadow and Dr. Chalmers Mitchell have successively shown (p. 436). But the length of the gut, and the thickness of the walls thereof, are largely determined by the nature of the food to be assimilated. Thus, in purely frugivorous and insectivorous birds the gut is very short, while it reaches its maximum length in species which feed upon fish, carrion, grain and green vegetable matter. The lumen of the gut in short-gutted forms is generally very wide, while in piscivorous birds the walls of this canal are always very thick — a possible contrivance to lessen the danger of perforation by fish-bones. At the junction of the small and large intestines there may be found a pair of creca or blind diverticula, guarded by a valve which allows the semi-fsecal matter to pass into these pouches, but prevents any backward movement into the small intestine (ileum). In some birds, such as the African Ostrich, Rhea (111. 7, p. 23) and the Gallinae these cseca are of relatively enormous size ; they are also very large in some of the Wading-birds (Limicolae), in Owls and in Night-jars, Rollers, Bee-eaters and Cuckoos which are insectivorous. In fish-eating birds they are of relatively small size, and in some species are quite degenerate. In some species they are reduced to mere wart-like bodies, of which one may be wanting altogether, e.g.. Herons and Petrels, or both may have com- pletely disappeared as in many Pigeons, Parrots, Kingfishers and the Swifts, for example. In Struthio and Rhea the aggregate volume of these ap- pendages, as Dr. Hans Gadow has pointed out, may surpass that of the rest of the intestinal canal. These pouches do not present any great range in the matter of shape. As a rule they are cylindrical. But in the Owls they assume the form of inverted Florence-flasks ; while in the Martineta Tinamou {Calodromas elegans) they assume a truly remarkable form, having the semblance of a bunch of grapes ! (111. 7, p. 22). 22 A HISTORY OF BIRDS The Cffica appear to function as digestive organs when fully developed ; but in some cases they seem to have assumed a new character. Such instances appear to obtain in many cases where these organs would seem, judged solely b}' their small size, to be degenerate, as, for example, in Passeres. But here, as Dr. Chalmers Mitchell has pointed out, the walls of these extremely reduced organs contain lymphoid tissue, though what function they serve, whether secretory or excretory, is yet unknown. Thecsca of the Owls similarly, at their ends, con- tain masses of lymphoid tissue, while in Ducks and Fowls this occurs in scattered patches. Thus, while some reduced ca;ca are certainly degenerate and functionless, others, though re- duced, still play a more or less important role in the meta- bolism of the body. But the presence of these organs presents some curious anomalies, which seem to show that although their develop- ment is correlated with certain kinds of diet, this relation is by no means always maintained. The diurnal birds of prey and the Owls afford the most striking illustration of this peculiarity. Both are now flesh eaters, and the former have apparently in consequence lost them, yet in the latter they are of large size. Some of the Owls, it is true, still partake freely of insect food, but so also do many of the smaller Falcons, which indeed live exclusively on this diet, yet they, like their larger brethren, are minus these organs. One must assume that they were lost before the insect diet became fixed, and so could not be re- developed. But it is clear that they are not essential to the digestion of insect food, and equally clear that the substitution of a carnivorous diet need not bring about their dissolution. The rectum, like that of reptiles, terminates in a cloaca di- vided into a series of more or less distinct chambers, the copro- daeum, urodi^eum and proctodaium, into which last opens the " Bursa Fabricii," an organ of unknown function, peculiar to birds, and largest in nestlings ; into the uroda^um open the kidney and the genital-ducts. The coproda^um retains the faecal and urinary matter until ready for expulsion. The Circulatory System The main features of the circulatory system may be very briefly summarised. III. 7. — Types OF the C/eca, or Blind Gut, of I. Rhea. II. Owl. III. Martineta Tinamou INTRODUCTORY 25 Birds differ from Reptiles and agree with the Mammalia in having a completely four-chambered heart, whereby the ad- mixture of arterial and venous blood is prevented. The heart of birds, however, differs in important respects from that of mammals. Owing to their excessive activity the heart-beats of the bird are quicker than in any other animals, numbering 120 to the minute during rest, and during flight reaching a far higher figure. In a bird which has just alighted the pulsations are beyond the count of the ear. Birds, like mammals, have but a single aortic arch, but while in the former this is the left, in the latter it is the right of the originally double arch which persists. The corresponding arch of the opposite side, in both cases, gives rise to part of the subclavian artery. The carotid arteries exhibit some interest- ing modifications, but these appear, like so many other char- acters, to have no bearing, no traceable bearing, on the struggle for existence. And the same remarks apply to the femoral arteries which may be supplanted by the sciatic. Though attempts have been made to use these vessels for taxonomic purposes, they have been only partially successful. The Pen- guins alone among birds develop a rete mirable, which is, of course, connected with their diving habits, though other diving birds, it is to be remarked, have not developed a similar ar- rangement of the blood-vessels, which is met with again in the Cetacea among the mammals. An ingenious use of the veins supplying the intestinal mesentry has been made by Dr. Chalmers Mitchell, but the discussion of this, as of other peculi- arities of the vascular system, does not come within the scope of this work. During the work of brooding it is to be remarked the blood-vessels of the abdomen become greatly distended, and form large " inflamed " areas known as brood spots, which, applied to the surface of the egg during incubation, generate the heat necessary for the development of the growing chick. The Muscular System The muscular system of birds presents no characters which have any really important bearing on the problems with which this book is concerned. Nevertheless, interesting illustrations 26 A HISTORY OF BIRDS could be drawn therefrom, did space permit, of the way in which muscles, originally single, become split up to form two or more distinct bodies, which in turn undergo further modifi- cation and often degeneration. Both the wing and the thigh furnish examples of this kind. Two instances thereof must suffice. The first of these shall be taken from the wing, and shall be confined to a single group of birds, the Passeres. The muscle selected is that known as the deltoidcns, which, in its primitive " archicentric " condition, arises in part from the acromion of the scapula and the inner, free face of the furcula, and in part from the os huniero scapularc and the crista lateralis of the humerus. Running down the arm in the form of a thick " belly," it is inserted into the ectepicondylar process of the humerus, e.g., the Birds of Paradise. The evolution of this into two distinct muscles can be easily traced. As specialisa- tion proceeds the belly splits into two portions, the origin and insertions remaining the same, as in the Common Starling. This is the beginning of the transformation into distinct longus and brevis portions. In the Corvida^ the longus portion becomes degenerate, fusing with the brevis portion which is continued downwards to terminate in a tendon at the usual point of insertion. In the primitive "Broad-bills" iyEurylce- niidiE), on the other hand, it is the brevis portion which is degenerate, and which terminates on the upper third of the humerus shaft, leaving the longus portion to effect the usual union with the distal end of the humerus. What factors have brought about this splitting of the muscle, and what have de- termined the survival of the brevis portion in one and of the longus portion in another, no man can say. Nor does it seem that these changes can have any bearing on the problems of existence. A similar illustration is furnished by the " Ambiens" muscle of the thigh — a reptilian heritage. In its fully developed con- dition this muscle arises from a projecting spine on the pelvis, beneath and in front of the acetabulum — the pectineal process — and descending the inner surface of the thigh crosses the knee- cap in the form of a tendon, and turning downwards joins the perforated flexor muscle for the second, third and fourth digit {Flexor perforans iudicis, niedii and annularis), splitting up for '^/f^.- J m h - {Ossifiagagigantca)^hy\\\<^ either in deep crevices or in burrows, though but the merest apology for a nest is ever made, and this may be wanting. The Tropic- birds {PhiCtlwn) nests in holes in cliffs, e.g., P. nibricanda, or, when these are wanting, in holes in trees, eg.., P. fulus. Among the Anserine birds we find the Golden-eye duck {Chxn- gula glaucion) breeding in holes in trees, and the Sheld -ducks {Tadorna) in burrows, usually those excavated by rabbits. But these birds will also, when ready-made holes are wanting, dig for themselves. Where rabbit-burrows are used it appears to be a common practice to lengthen the tunnel leading to the brood chamber, and in one instance this was found nearly sixteen feet from the entrance, and seven feet below the surface ! The Puffins again, among the Auk-tribe, breed in rabbit-burrows, or in burrows of their own making, or in crevices of rocks. Where rabbit-burrows are to be had they will not scruple to eject the rightful owners should there be no deserted tenements in the neighourhood. Among the Pigeons we find the Rock-dove breeding in caves or deep fissures, and the Stock-dove in rabbit- burrows, or holes in trees, and also in deserted squirrel '• dreys," or thick ivy on old walls. The Parrots all breed in holes, save only the Quaker-parrot {Myopsittacns nionacJius), which builds a ntst of sticks, a huge pile, containing a central chamber, .so that 176 A HISTORY OF BIRDS the bird may almost be said to build a hole ! Turning now to the " Coraciiform " birds we find that the majority breed in holes in trees, or in burrows. The Kingfishers, Bee-eaters, Hoopoes, Owls and the Woodpeckers and their allies serve as good examples in this connection. The Bee-eaters especially deserve mention, since these birds dig for themselves deep shafts sloping obliquely from the surface and descending as much as ten feet, at the bottom of which a slight nest of feathers is constructed. Among the perching birds a considerable number breed in holes, while the most striking burrower is the Sand-martin, whose nesting colonies must be familiar even to those who are not particularly interested in Ornithology. It would only be wearisome to describe in detail the nature of the preparations made for the reception of the eggs. Suffice it to say that in the majority of cases little or no nest is made, the eggs, when laid in hollow trees, being deposited on the rotten wood at the bottom of the hole ; but where a burrow is made, in sandbanks, for example, a few leaves or grass are commonly introduced. It would seem, however, that in some cases the practice of nesting in a hole is of comparatively recent date, as for instance, with the Golden-eye and Sheld-ducks, which still make a nest of vegetable matter, lined with down plucked by the female from her breast. The Kingfishers again differ among themselves. The fish-eating species build no nest, but lay their eggs on the disgorged remains, the hard parts of the fish and Crustacea on which they feed ; but those which feed on insects or fruit appear to lay their eggs on a roughly con- structed bed of leaves and straws (see also p. 192). Another and more important aspect of this subject is the fact that not only do the burrowing species exhibit no sort of special adaptation for the work of burrowing, but some even appear to suffer therefrom : the beaks of the Bee-eaters, for example, being quite worn down by their labours, a fact which becomes the more remarkable when we reflect that the most fragile of all these shaft-driving birds, the Sand-martins, appear to suffer in no way by their digging operations, even though they have the smallest of beaks. As a rule, probably, the work of excavation is carried on by the aid of the feet, as in the case of the Sheld-duck and Burrowing-owl {Speotyto), but with the Kingfishers and the REPRODUCTION— NIDIFICATION 177 fragile Bee-eaters and Sand-martins, the beak alone is employed in digging, but the feet eject the loose earth, the feet indeed of these birds being remarkably small and delicate. The two last-named species, for their size, bore really remarkably long tunnels, those of the Sand-martins extending in an upward direction for a distance of four or five feet, or even longer, when the tunnel terminates in a chamber of some six inches in diameter, the floor of which is covered with a little grass, or, if near the sea, with sea-weed and a few feathers. Both sexes combine in the work of excavation, which is carried on only during the early hours of the morning. Bit by bit the soil is removed, and often when the work is almost half-way through a stone will be encountered, and if this be too large, then there is nothing for it but to make a fresh start in another place. Once completed, however, the burrow is used year after year. The sides of a sand-pit are chosen for preference, but the middle of a bluff a hundred feet high, or a thin layer of mould of some eighteen inches thick, capping the side of a chalk- cutting, will serve the purpose equally well. Nay, further, they will, as in Norway, utilise the turf-roof of a hut, or a hole in a wall, and they have been known to take advantage of huge heaps of sawdust ! That most enthusiastic naturalist Waterton even induced them to take possession of a series of drain- pipes. The common Kingfisher, unlike the Sand-martin, is a solitary bird. Whenever possible choosing the deserted burrow of a water-vole, it will, when such a ready-made tenement is not to be had, dig for itself According to some indeed this practice is invariably followed. The length of the burrow is roughly about the same as that of the Sand-martin, and simi- larly this terminates in a wide chamber, which, as we have already stated, is soon covered with a layer of fish-bones and other indigestible matter ejected by the builders, and on this the eggs are laid. Though in course of time this mass gets beaten down and forms, by the adherence of the debris, a more or less coherent mass, no real nest is ever built by these birds. It would seem, as we have already remarked, that nest- building had its origin in an attempt to secure comfort in brood- ing where the eggs were laid on cold or damp ground. This being so, it is easy to understand how birds which had thus 12 178 A HISTORY OF BIRDS acquired this habit should continue to make similar preparations for brooding when for'some other reason — to escape floods or enemies — they elected to build in trees, instead of reverting to the older custom of seeking a hole in the trunk thereof. Such a nest would necessarily be of a loose and rough character, but, since it served its purpose, many to this present day have not improved thereon. The Crows, Pigeons, Herons, and Accipitrine birds, such as the Eagles, for example, build only a rough platform of sticks. In the case of the Pigeons it is so frail indeed that daylight can be seen through it. Nevertheless, these structures are much more durable than one might sup- pose, and in successive seasons are often either repaired or a fresh nest is built upon the top of the old one, a practice followed by many birds of prey, until at last, as in the case of the Osprey, for instance, the accumulated mass, if built in a tree, falls of its own weight. Nest of the Hammer Head Some species, however, have improved upon this platform structure, piling up sticks to form a roof or dome, such as, for example, may be seen in the nests of the Magpie, the African " Hammer-head " {Scopus umbrettd) and the Quaker-parrot • REPRODUCTION— NIDIFICATION 179 {Myopsitiacus nionachiis), the only Parrot, by the way, which builds a nest, all other members of the order nesting in holes in trees ; thus the domed nest in this case is significant. The transition from the platform of twigs to the more highly finished nests such as we must now pass on to examine may well be studied in the work of the Hawfinch {Coccothraustes vulgaris) and the Bullfinch {Pyrrhula vulgaris), which to a platform of twigs adds a neatly wrought central cup composed of rootlets and fine hair. From nests such as these w^e may pass, by a series of infinite gradations, to cup-shaped structures of exquisite beauty, composed entirely of the finest materials. To follow up these gradations in detail would be an almost impossible task ; suffice it to say that we find in the earlier phases of this evolution that mud is a material commonly used. This fact is of no small significance, since, as we shall show later, it is to this habit that the use of mud exclusively for building material owes its origin. The larger Thrushes all employ mud as an agent in the construction of their nests, which are composed of sticks, roots and moss, held together by an admixture of clay, while the interior of the nest is cup-shaped and lined with fine roots and grass. But the Common Thrush {Turdus viusicus) has become an expert mason, lining its nest with an admixture of mud, rotten wood and cow-dung in varying proportions. So per- fectly is this plaster-work done that during wet seasons the nest often becomes filled with water, to the destruction of the eggs of course. As the evolution of the nest proceeds the use both of sticks and mud is discarded, the whole structure being composed simply of deftly interwoven root-fibres, grass and moss, with a lining of feathers and fine hairs, commonly pro- cured from the tails of horses. The nest of our Common Redstart {Ruticilla phcenicurus) answers to this description. More perfect and more beautiful are the nests of the Goldfinch {Carduelis elegans) and of the Chaffinch {Fringilla avlebs), the former choosing fine twigs of fir, fine roots and wool, lining the whole with willow-down, feathers and hair. The last-named species is a yet more skilful architect. Wool ap- pears to form the staple building material, and into this moss and lichens of various colours are dexterously woven, producing a shapely cup of uniform texture and singular beauty. Extern- i8o A HISTORY OF BIRDS ally it is studded with such lichens as best accord with the surroundings of the nest, and bits of birch-bark, these final additions being held in position by the aid of spiders' webs. Inside the wool is still more closely felted and interwoven with fine hairs, while the final touches are given by a few feathers deftly arranged, often so as to curl over and partly conceal the eggs. This exquisite fabric appears to be the work of the female only, and takes about three or four days in the weaving. No less beautiful is the nest of the Long-tailed Tit {Acredula caudata). It has indeed been justly described by the late Professor Newton as " a marvel of construction, combining beauty with safety and warmth ". Nearly oval in shape, and with a small hole on one side by way of a door, it is composed mainly of moss and wool, held together by spiders' webs ; externally it is encrusted with lichens so as to harmonise with its surroundings, while it is lined with feathers. This lining would appear to entail a prodigious amount of labour, since Mac- gillivray found in one of these nests no less than 2,379 feathers, chiefly those of the Pheasant, Wood-pigeon, Rook and Par- tridge. Generally this wonderful nursery is placed in the middle of a thick bush, and so firmly is it bound to the sup- porting branches that these must be removed with the nest if the latter is to be taken intact. The cock and hen appear to work alternately in its construction, which may be completed in as short a time as twelve days, but a longer period is usually required for this purpose. Usually nests which are built amid bushes or trees either rest upon some big bough just where it leaves the trunk, or are lodged between the parting-ways of several small branches. Often, however, these branches are included within the frame- work of the nest, as in the case of the Long-tailed Tit, for ex- ample. And herein we probably have the origin of pensile nests, of which a few examples shall be described here. But before proceeding to these it will be necessary to refer to a type of nest which, fixed between vertical pillars, occupies an intermediate place between nests interwoven between forking branches and suspended nests. A good example of such a nest is found in that of the Reed-warbler {Acrocephalus streperus). The building material selected by this little bird consists of the seed-heads of reeds and long grass mixed with wool. The REPRODUCTION— NIDIFICATION i8i grass seems to form the foundation, and is wound horizontally round about the stems of three or four tall reeds, while the seed- heads and wool are used to fill up the interstices. The com- plete nest measures about five inches in depth, three inches across the top, enclosing a cavity of some three inches in depth, lined with very fine grass and long hairs. So securely is this cradle fixed, and so great is its depth, that even when the supporting reeds are bent low by the wind, so low that the nest may almost touch the water, the eggs will not roll out, nor is the sitting bird apparently discomfited. Pensile nests are built by many species, though the more remarkable instances must be studied in the birds of other lands. At least one good example, however, may not infrequently be met with in Great Britain, the builder thereof being the smallest of our native birds — the Golden-crested Wren {Regulus cris- tatus). The materials chosen are the softest moss and wool, held together by means of spiders' webs and long grasses, while small feathers are finally added to form the lining. The whole structure is suspended after the fashion of a hammock, to the under side of the slender twigs at the end of a branch of such trees as fir, yew or cedar, only with this difference, that while the hammocks swing at the ends of long cords this nest is braced up close to the branch. The Golden Oriole similarly suspends its nest, which is built up of sheep's wool, fibres of roots and long slender stems of grass beautifully interwoven, while flowering heads of grasses are used to form a lining in the place of feathers. But while the Oriole appears always to sus- pend its nest, this rule is not so closely followed by the Golden- crested Wren, which will occasionally build upon the upper surface of a branch, or against the trunk of a tree upon the base of a diverging branch, thus reverting to the more normal habit. The purse-like nests of the Flower Peckers {Diceinn) and of the Penduline Tits (p. 184) and Humming-birds (p. 182) are even more beautiful examples of nest-building, being made al- most entirely of cotton-down, as also are those of the Crowned Titmice {ALgithalus). It has already been shown that species which commonly build a pensile nest will on occasion revert to the normal fashion of resting the nest on the bough. Similarly, when a number of distinct species are found to have acquired the l82 A HISTORY OF BIRDS practice of building a pensile nest, it will often be found that other species of the same group build after the older fashion, as witness the Weaver-birds (p. 183) and Humming-birds, for example. The nests of the latter, of whichever type, are of III. 25. — Nest of the Humming-bird (Plicethornis cnrynome). Pensile Type. great beauty, and formed principally of a felting of cotton- down and spiders' webs. Mostly cup-shaped, and often be- studded externally with lichen, they are small even relatively to the size of the bird, so much so that in one instance it is re- corded that as the young grew in size the walls were heightened by the parents, until at last the nest was more than twice as big as when the eggs were laid and hatched ! Where the nest is suspended it is attached either to the tendril or stem of some climbing plant, or to the side of a drooping palm leaf When hanging freely some species, it is said, load one side of the nest with a stone or bits of earth to secure a proper balance, and this device is again met with in the case of some of the Weaver- birds. REPRODUCTION— NIDIFICATION 183 More remarkable structures than any we have yet noticed are the hanging nests of many of the Sun-birds, Hangnests, Weaver-birds and lastly the "Tailor-bird". These nests afford us a forcible illustration of the apathy of Ornithologists for anything more than mere collecting or species-making, or the record of bald or obvious statements of fact; inasmuch as among the Hangnests {Icteridce) a great diversity in the form of the nest and in its site is exhibited, some species nesting on the ground, others in reeds or tussocks of grass, and others again in trees, these last presenting a very remarkable degree of specialisation in their architecture, while those of the first of this series are simple in type. Yet no attempt has been made to trace out the several stages in the evolution from the one extreme to the other. Unfortunately, this cannot be done here, as owing to neglect of this most interesting question sufficient material has not been collected to make the chain complete. The Sun-birds appear always to suspend their nests, which are built of fine hair-like roots, fine grass and wool. They are pocket-shaped structures provided with a more or less steeple- like dome, the apex of which seems to suspend the whole, while above the entrance it is produced to form deep over- hanging eaves. The Hangnests of North and South America {Icteridce) build, as we have just remarked, various kinds of nests, but we can here refer only to the very highly specialised suspended type, which have the shape of a Florence-flask with an enormously long neck. These nests are made of long, fine grass with an entrance hole near the middle of the flask. Yet more wonderful are the nests of some of the Weaver-birds — and here also transitional types of increasing complexity are to be found — the typical forms of which may be described as retort- shaped. Strongly wrought of fine grass stems or fine roots, these nests are globular in form and suspended by a long rope, while entrance is gained by a tubular aperture generally placed at the bottom of the nest •, it forms indeed a sort of covered way added on to the more normal pocket-shaped structures of this kind built by other species. Both sexes are .said to take part in the work of building, the rope-like suspensory portion being first formed, and this is continued downwards to end in a large loop, the inner entrance to the nest. From this loop the sides 1 84 A HISTORY OF BIRDS of the chamber are started, the female receiving the ends of the threads pushed through from the outside by her mate. One species, Ploccipasser inaliali, make two " spouts " or covered ways to the brood chamber, while Ploceus baya balances its nursery by means of lumps of clay, as is also done by some Humming-birds (p. 182). It would seem that the addition of this tubular entrance is a contrivance to prevent the entrance of snakes. To achieve this end Salvin's Swift and the Penduline Tits add a false, blind entrance, their nests being exposed to the attacks of lizards. The nest of Salvin's Swifts, Panyptila Sancti-liierononiyi, is to be reckoned among the most remarkable of the pendant nests, being constructed entirely of seeds collected in mid-air, held together by a salivary secretion, which is also used as a cement for the attachment of this curious tubular structure. The felted nests of the Penduline Tits of the Genus Reinisa deserve some special notice. In texture the walls of this nursery, both in appearance and to the touch, resemble that of the finest felt carpet, being made of cotton and seed-down. Towards the upper end of the nest is a funnel-shaped opening leading to the chamber, and below this a small pocket which is supposed by some to be a roosting place for the male. On the other hand, according to others, the sitting bird draws in the tubular entrance before going to sleep so that snakes or lizards fumbling about the pocket or false entrance give the alarm, when the bird escapes by pushing a hole through the back of the nest. One other example of pendant nests and we must conclude this section : this is furnished by the Tailor-bird {Siitoria longicauda). It is an extraordinary cradle that this creature makes, inasmuch as it draws together the edges of a leaf and holds them in position by stitching them, either by vegetable fibres or threads spun by man— when the nest is built near human habitations. Sometimes two leaves are similarly held. The pocket thus formed is then filled with cotton-down and other vegetable matter and soft material. Just as various stages in the evolution of the highly finished nests of the Hang- nests and Weaver-birds are to be met with, so in the case of the Tailor-bird we find an allied species, the Fan-tailed Warbler {Cisticola cursitans) building a globular nest amid grass stems and binding the free ends together above it. THE NKST OF REMEZIA REPRODUCTION— NIDIFICATION 185 We must pass now to a brief survey of such nests as are built of mud, wherein it will be seen that the selection of this material has been independently made by the most diverse orders of birds, some of which have acquired the most wonder- ful skill and ingenuity in the use of this material. Mud is employed, as the foregoing pages have shown, by many birds either to form a cement in holding together other materials, or more remarkable still, to serve as a balance to nests suspended by a single strand. Originally used as a cement only, it is easy to see how, when the normal stable materials were hard to come by, mud alone came to be em- ployed. But whether the shapes of the mud-nests of to-day are replicas of the older nests built of a mixture of materials, or whether the evolution in intricacy which is to be met with is independent of such models, we cannot say. The simplest types of mud-nests are cup-shaped, or rather basin-shaped structures such as those built by the Grey Strut- hidea and Conorax of Australia on the branches of trees ; or of the huge columnar piles hollowed at the top built by the Flamingo in swamps. The mud-nests of the Swallow and Martin need no description here, but it is to be noted the other mud-building members of this tribe show a wonderful ingenuity in the construction of their nurseries, some of those of the Cliff- swallows of the Genus Pctrodiclidon, for example, building retort- shaped nests of no little beauty. It would seem, however, that, like the Swallows generally, they originally built in holes, in- asmuch as a North American species, P. pyrrkouota, will fre- quently build in holes, around the entrance of which they construct a rim of clay. Probably the size of this rim was increased in proportion to the smallness of the hole, until at last the entire nest came to be of mud whenever holes were wanting. The nests of Australian Cliff-swallows are said to be constructed by several birds working together, one remaining inside the nest and receiving the pellets as they are brought by its companions. The entrance tubes to these nests are often eight or nine inches in length. But observations are wanting as to whether these birds build their nests on this principle of mutual help, or whether they are polygamous, each nest being built by the male and his mates. But the most noteworthy of nests of this kind is that built by the Oven-bird {Fiiniarins) 1 86 A HISTORY OF BIRDS of South America. It is a remarkable structure, thick-walled, globular and of great size. For the most part made of clay and dung, the builders, however, evidently understand the value of hair and long grass as binding materials, for these are worked into the mass just as hair is used in mortar in the construction of human dwellings. In section it is found to contain a central chamber, with a long passage running partly round it, the inner chamber being lined with fine grass. Since the materials for building can only be obtained in damp weather this edifice takes several months to build. It is further to be noted that while three distinct species all build precisely similar nests, two adopt a more conventional style of nursery. One of these, Fnrnarius figulus, builds a nest of sticks, while the other, F. torridus, breeds in holes in banks. Among the builders of the more elaborate nests where finely divided materials are used, cement, in the form of a secretion of the salivary glands, is commonly employed. This is the case, as we have already seen, in the nests of Salvin's Swift (p. 184). But there are certain Swifts, of the Genus Collocalia — a genus extending from the Indo-Malayan countries and Australia — which build their nests almost, or entirely, of inspissated saliva. These birds attach their small saucer-shaped cradles to the walls of caves, generally mixing grass or feathers with this secreted matter. But the species known as the Esculent Swiftlet {Col- localia fucipJiagd) commonly dispenses with all foreign materials and uses the products of the salivary glands entirely, and it is these nests which furnish the material for the " birds'-nest soup" considered so great a delicacy by the Chinese. The collection of these nests constitutes an important industry, as may be seen from the fact that from Borneo alone, over three and a half million nests have been exported in a single year. As might be supposed, these birds build in huge colonies, and while in some cases the caves are approached by water, in others the floor is dry and covered with a deposit of guano varying from eighteen to thirty feet thick ! No less remarkable are the nests of some of the Tree-swifts of the Genus Macropteryx since these are made up of a salivary secretion intermixed with bits of bark, while in point of size they represent the smallest nests known — relatively to the size of the builders. About an inch and three-quarters across and half an III. 26.— Nest of Oven-Bird REPRODUCTION— NIDIFICATION 189 inch in depth, the walls of this fragile structure do not exceed an eighth of an inch in thickness. In this tiny space a single egg is laid which, in most species of the genus, appears to be incub- ated in the usual manner, though at this time, owing to the large si'/.e of the bird, the nest becomes invisible. But one species, the Javan Tree-swift {M. /o//^<^//^('//f//s), builds so flimsily — the walls of the nest being no thicker than parchment — that the sitting bird has to rest her weight upon the bough, to the side of which the nest is attached, contriving so that the abdomen is in contact with the egg. We have already alluded to the fact that many birds breed in colonies, often of vast extent, as in the case of Penguins, Alba- trosses, Flamingoes and the members of the Gull tribe, which may often be numbered by millions. Here the nests, often but the rudest structures, are all separate, though they may be divided only by a few inches. Smaller colonies are formed by many species, notably by the Swifts and Swallows, where the nests, sometimes to the number of several hundreds, are fre- quently so crowded as to touch one another. And thus we find the way paved for the evolution of a yet more intimate relation between associated nests. Yet but two species appear to have adopted the practice. One of these is a Weaver-bird {Ploceida)^ the other the Sociable Grosbeak of Africa {PJiilJiatcerus socius). The enormous umbrella-shaped, thatch-like masses which these birds combine to erect in trees have been known to contain as many as three hundred and twenty-seven separate nests, but whether the whole is produced by the packing together of separ- ately constructed nests, or whether the nesting tunnels and chambers are driven through after the common foundation has been built, does not seem to be known ! Probably this arboreal " warren " is formed by the interlock- ing of separate nests, since this method of building is also practised by the Wax-wing of San Domingo {Dul/is dominlms), several pairs of which will often join their nests, made of twigs, into a circular mass. The huge nests of the Osprey and Secretary-bird present us with yet another aspect of colony formation among birds ; for both species permit small Passerine birds to build their nests within the outer walls of the castles of their overlords, much in I90 A HISTORY OF BIRDS the same way as Sparrows, Starlings and Swifts build within the roofs of human dwellings. In broad outline the main facts concerning the construction of nests, and the sites in which they are placed, have now been surveyed, and here and there exceptions to the rule have been cited. To these exceptional cases it is proposed to add a few others, inasmuch as while some yet seem inexplicable, others throw some light at least on the question of the evolution of nest-building. That some species are remarkably conservative in the con- struction of their nests, and in the selection of its site, while others are not a little erratic in these matters, is well known. But most of these instances will be found on examination to be determined by circumstances. Thus Rooks have been known to build their nests of wire, of which an abundant supply was to be obtained from refuse heaps in the neighbourhood, while sticks were probably scarce, possibly having been appropriated by earlier builders. Robins and Blue Titmice choose most curious places wherein to build ; and here again we have an explanation in that both these birds seek the neighbourhood of human dwellings during the nesting period, thereby displaying a confidence that happily is not often abused. Similarly, the fact that Cormorants and Herons, and even the lordly Eagle, will build either in trees, precipitous rocks, or on the ground is explained by the nature of the environment. Where lofty trees are available all seem to prefer the security they offer. But the exceptions to which reference is here particularly made are those which break with the traditions of the tribe in a much more striking fashion, inasmuch as, in the case of large groups of birds especially, some species are found which have developed idiosyncrasies in this matter which seem to defy solu- tion ; and while with some species these departures are sporadic, it is often found that with others of the same group they have become normal. Thus among the Duck tribe the ground is the normal nesting-place, but the Mallard often elects to nest in a hole in a tree thirty or forty feet from the ground ; with the Golden-eye Duck {Clangula glaucion) such a site is invariably chosen. Among the Plover tribe there is a remarkable lack of NEST OP^ THK HERRING fiULL A PRIMITIVE NEST: NEST OF THE RINGED PLOVER REPRODUCTION— NIDIFICATION 191 uniformity and tradition, so to speak, in the matter of nest- building. The majority lay their eggs on the bare ground, in a slight natural depression, or in a shallow cup formed by the birds themselves. The site chosen may be meadow-land or barren heath, or sandy or shingly beaches. The Redshank alone among the Plovers weaves a dome of growing grass above its eggs. The Little Ringed Plover, on the other hand, trusts to the protective resemblance of its eggs to their immediate surroundings. In some cases these eggs are deposited in the bare sand or shingle ; in others a pavement of small stones or shells is prepared for their reception. The Wood Sandpiper {Totanus glareola) and the Green Sandpiper {T. ochropus) differ in yet more striking fashion from their congeners. The former appears generally to fashion a rude nest on the ground, near water, but in Siberia it generally uses the deserted nests of Fieldfares high up in trees ! Similarly, the Green Sandpiper nests occasionally on the ground or on moss-covered stumps, but more usually the eggs are laid in old squirrels' "dreys," the nests of Song and Missel-thrushes, Black- birds, Jays and Ring-doves ! The Gull tribe normally nest on the ground, content with the merest apology for a nursery, yet, on occasion, they will build in trees thirty feet or more from the ground. The Terns again, as may be seen on a visit to any breeding colony on our coasts, display considerable individual differences in this respect. The Common Tern, for example {Sterna fluviatilis), may be content with a bare scrape in the sand, or may build a quite bulky nest of weeds. These differences seem to be inexplicable, to be due to individual idiosyncrasies, since various gradations of perfection, from a mere bare depression to a relatively elaborate nest, may be found in the same colony, and within a relatively small area. The innate capacity for building displayed by the British species of Tern is possessed in a more highly developed and more stable degree in some exotic species, as for example in the Noddy-tern {Anous stolidus). This bird commonly rears its young in trees or low bushes, building a nest of mud, sea-weed and grass. More curious still, the White-tern {Gygis Candida) will lay its single &^g on a coral reef, or any slight cavity of 192 A HISTORY OF BIRDS a branch, or at the base of a broad leaf-stalk. Thus Dr. H. O. Forbes, describing the nesting of this bird in the Cocos Keeling Islands, remarks: " Its solitary egg is deposited on the leaf of a young cocoa-nut palm, at the time when the leaf has rotated from its vertical position to one nearly at right angles to the stem. The egg is laid in the narrow angular gape between two leaflets on the summit of the arch of the leaf, where it rests securely, without a scrap of nest, . . . yet defying the heaving and twisting of the leaves in the strongest winds. The leaf, as in all palms, goes on drooping further and further till it falls ; and among the settlers it is a subject of keen betting, when they see a Tern sitting on an ominously withered leaf, whether the young bird will be hatched or not before the leaf falls. The result . . . has always been in favour of the bird : if the leaf falls in the afternoon, the Tern will have escaped from the egg in the morning!" More commonly, it would seem, however, that this bird deposits its egg on the bare limb of a tree without any attempt at safeguarding whatever, yet accidents seem rarely, if ever, to happen. Motives of security probably prompt the Dipper {Cinclus aquaticus) of our northern streams to build its dome-shaped nest of moss in some cranny behind a cascade, so that the bird must dash through the water every time it enters or leaves the nest ; but there is no evidence to show whether this site is invariably chosen when cascades are to be met with. Similarly, security may be the reason why the Ruddy Kingfisher {Halcyon coroniandus) of North-West Borneo places its eggs in the pendulous nest of a peculiarly vicious bee, for certainly the eggs can only be taken after the destruction of the bees ! The Rufous Woodpecker {JMia-opterus phoeoceps) has been taken near Darjiling from the deserted nests of ants, nests resemb- ling in shape those of the wasp (Vespa brittanica). It would seem that the builders are summarily ejected by the birds, and since ants form their staple food it is probable that ,the victims are eaten as they surrender ! Deserted ant-hills are commonly used by many species of insectivorous Kingfishers, but this is not surprising when it is remembered that so many select sand- banks wherein to tunnel their nurseries. This list of peculiar nesting sites might be greatly extended, but sufficient instances have perhaps been cited to draw atten- REPRODUCTION— NIDIFICATION 193 tion to this aspect of nest-building among birds. Whether we shall ever learn anything of the factors which have brought about these departures depends entirely upon the observations, of those fortunate enough to be able to study the facts in the field. This chapter would be incomplete without a brief comment on the question raised by Dr. Alfred Russel Wallace, years ago, as to whether birds build by instinct or by imitation. Without doubt he did much to confuse the issues at stake by com- paring the nest-building of birds with the house-building of man : an obviously false analogy. In spite of the dogmatic assertions of this eminent naturalist, there is absolutely not only no evidence in support of his contention that birds build by imitation, but all the known facts are directly against him. He first argued that the art of nest-building was acquired by the young bird while in the nest. That is to say, between the intervals of sleep and feeding it takes mental notes of the construction of its cradle, against the day when these notes may be useful ! Relinquishing this, he next suggests that the young bird, just before building its first nest, makes a survey of the cradles of others of its own species; and finally, that young birds must pair with old birds and so learn the secret from their more experienced mates ! But it is all very well to talk of imitation, but who set the fashion of each type of nest originally? No, there can be no question of imitation. Nest- building is a product of selection and is instinctive. This is shown by the fact that wild birds taken from the nest before they can see, and kept in captivity under suitable conditions, will, at the appropriate time, build a nest typical of their species. That a bird's first nest is less perfect than succeeding nests has often been urged, and this is probable ; for practice necessarily leads to perfection. There is nothing remarkable, indeed, about the part played by instinct in this matter. Young spiders yet but an hour old will at once proceed to spin a web as perfect as that of an adult, and there can be no question of imitation here. A caterpillar when full-grown will spin for itself a most elaborate cocoon, or suspend itself by the tail, and place a girdle round its body to bear its weight in the chrysalis stage, yet there can be no factor other than " instinct " at work to guide it. For this act is performed but once in its life, and is carried out in isolation. 13 194 A HISTORY OF BIRDS But Dr. Wallace also implies that birds employ a certain amount of reasoning in their building, or rather, perhaps, that they act on suggestion, on the stimulus of their environment. That when impelled to build they seize on the materials nearest at hand. Thus the Wren " frequenting hedgerows and low thickets, builds its nest generally of moss, a material always found where it lives. ..." " Rooks dig in pastures and ploughed fields for grubs, and in doing so must continually encounter roots and fibres. These are used to line its nest." But what about the foundation of the nest ? And again : " Swallows use clay and mud from the margins of the ponds and rivers over which they find their insect food. The materials of birds' nests . . . are, then, those which come first to hand." But the Sand- martin is equally partial to streams, yet this bird does not build a nest of mud, but laboriously drives tunnels in sandbanks and lines the further chamber with feathers ! Finally, he remarks : " The clumsy hooked bills, short necks and feet and heavy bodies of Parrots, render them quite incapable of building a nest. ..." But the Quaker-parrot {Myopsittacus inonachtis) builds a large domed nest of sticks, and is, moreover, no mean craftsman at weaving. The origin of nest-building, as we have suggested (p. 174), began probably with the ground-builders, which hit upon the device of collecting twigs or grass to form a dry bed while brooding, thereby preserving their eggs, while those less intelligent failed to rear offspring. The young of these more intelligent parents, inheriting this variation in the direction of increased intelligence, would, stimulated by the sexual impulse at the proper season, repeat the same tactics. With changes in the environment new needs arose and were similarly met by at least a i&\N individuals, and thus, by slow increments the gradual evolution of complex nests arose. Even to-day many stages can be traced in the growth and perfection of the more complex nests of any particular type, such as the pendant nests of the Weaver-birds, and Hangnests, for example (p, 183). While, as in the case of the Cliff-swallows (p. 185), we may even have a rever- sion of the older type of nests, inasmuch as when suitable holes are to be found a mud-rim around the entrance is all that is con- structed, the typical retort-shaped nest growing in inverse pro- portion to the size of the hole. CHAPTER XII REPRODUCTION— CONCERNING EGGS Number ot eggs in a "clutch". Shape of the egg. Size. Texture and thickness of the shell. Colours of eggs. Origin of the colours. Patterns of coloration. Colours of eggs in relation to classification. Coloration in relation to environment. White eggs and their meaning. Structure and composition of the egg. BIRDS, like their cousins the reptiles, are oviparous : but they differ markedly from the reptile in the relative fewness of the eggs laid in each " clutch " as well as in the fact that these eggs are commonly coloured externally. With regard to number it is to be noted that this may vary from a single egg, as in the case of the Guillemot, for example, to as many as twelve or even twenty, as in the Common Par- tridge. That is to say, except when more than one brood is reared in each year, this number is not exceeded ; but if the eggs be removed or destroyed, more are laid to replace them, and this may be repeated many times during each season, until the maternal instincts are gratified, or the bird becomes ex- hausted. Man has taken advantage of this fact to supply himself with food, or for other less excusable ends. Thus the Lap- wing, one of our most useful birds, is mercilessly robbed year by year to supply " delicacies " for the table, and similarly the colonies of Gulls and Guillemots are systematically plundered, the former supplying the shortage in the market of " Plovers' " eggs, the latter furnishing their ova for commercial purposes. As a rule, however, a few eggs are left to hatch, for the pur- pose of preserving the stock. The Eider-duck and the Golden- eye Duck are still more systematically victimised, the latter even being induced to lay in artificial nest-boxes. While in many species the number in each " clutch " varies considerably, as in the case of the Partridge, in others it is very 195 196 A HISTORY OF BIRDS constant, as for example in the Plover tribe, which lay three or four, or in the Gulls and Terns, which lay two or three, or of the Pigeons, which never exceed two. In form birds' eggs present certain peculiarities ; thus in the Owls, Bee-eaters and Diving Petrel they are spheroidal, and bi-conical in the Night-jar and Sand-grouse; in the Cormorants they present a long ellipse, while in many of the Plovers and Guillemots they are pyriform. Only in the case of pyriform eggs does shape appear to have any significance. Thus in the case of the Guillemot, which deposits a single egg on a bare ledge of rock in the face of some cliff, this shape is obviously advantageous, since, if blown by the wind, or struck by the bird as in diving off the ledge, instead of rolling over into the sea or on to the rocks below, it will revolve in a circle on its own axis ; though in spite of their shape thousands of eggs are annually lost, either because laid on too small or sloping a ledge, or because they are struck too violently by the sitting bird, as when it leaves the work of incubation through fright. In the case of the pyriform eggs of the Plovers this shape is of advantage, since it allows the eggs to be more closely packed — the sharp ends inwards — and so more easily covered by the sitting bird. This being so, it is a little surprising to find that even among nearly allied birds of this group pyriform eggs are by no means the rule. The size of the egg does not by any means always cor- respond in proportion with the size of the bird which laid it, but depends rather on the relative development of the newly hatched chick. Thus where the eggs are relatively large — com- pared with the size of the parent — the chick at hatching is able to run about and feed itself, under guidance, while on the other hand, when the egg is small the chick is hatched in an ex- tremely helpless state — before the eyes have opened, or the body has developed a covering of any sort (p. 246). In propor- tion to its size perhaps the Apteryx lays the largest egg. This bird indeed was described on one occasion as " the bird which lays eggs bigger than itself" ! By way of contrast a comparison is often made between the egg of the Humming-bird and that of the extinct yEpyornis, the cubic contents of whose egg equalled about three gallons. The Curlew, Raven and Guil- lemot are birds of similar size, and so also are the Snipe and REPRODUCTION— CONCERNING EGGS 197 Blackbird, but the contrast in the sizes of their eggs is enor- mous. Besides the variation as between chfferent species, there are to be found numerous instances of specific variations of a very considerable range which have become normal to such species. Of course variation within small limits occurs in eggs of all species : to these we do not refer here, nor have we in mind those abnormalities of size which so frequently occur. Re- markably small eggs containing no yolk, for example, frequently mark the first efforts of immature birds. But the variations to which we refer are such as are afforded by the great White Heron. This species occurs both in Europe and India, birds from the two regions being indistinguishable, yet the eggs of the European birds are always much larger than those taken in India. European eggs in the collections of the British Museum measure from 2*35 to 2*7 in. in length, while Indian specimens range from r88 to 2"38. Birds' eggs differ very considerably in the texture and relative thickness of the shell. In the matter of texture some, as in the case of the Tinamous, have their surface so highly polished as to look like burnished metal or highly glazed por- celain, while a very considerable gloss is commonly met with, as in the case of the Kingfishers and Woodpeckers. Ducks' eggs are remarkable for their peculiarly smooth, "greasy" sur- face, though the eggs of the Genus Erisniatnra must be taken as exceptions to this rule, since they are covered with coarse granu- lations ; and, curiously enough, the eggs of the allied Genus Bisiura, represented only by the Australian Musk-duck, are frequently similarly granulated, and when this is not the case they are of the normal Anserine type. The eggs of the Ibises offer similar differences, since in some genera they have a smooth surface, while in others it is rough. So far no ex- planation for these differences appears possible. This roughne.ss of texture attains its maximum among the Grebes, Flamin- goes and certain Cuckoos. The eggs of these birds have the shell incrusted with a chalky layer often of considerable thick- ness : often when this crust is scraped away a rich colouring is revealed, as in the case of the Cuckoos of the Genus Croto- phaga. In the allied Guira Cuckoo this chalky layer is deposited in the form of a coarse and irregular meshwork forming a 198 A HISTORY OF BIRDS tracery of white over a deep blue ground. Nothing appears to be known as to the possible use of this chalky layer, but in one case at least a possible explanation may be found. This case is furnished by the Razor-bill, but the interpretation offered may be more conveniently considered later (p. 209). The thickness of the shell varies within certain limits ; thus in some cases, especially among the smaller birds, the shell is so thin that the egg becomes translucent, as in the case of the Kingfisher, while among the Ostrich tribe it is relatively thick. While as a rule the surface of the egg is smooth, in some cases, especially among the Ostriches, the egg is deeply pitted, the Apteryx and Tinamous excepted. It has been stated that the texture and colour of the shell of eggs of hybrids can be distinguished from those of the pure species. It is conceivable that this may be so, but the conten- tion that the eggs of a hen mated with a cock of another species are similarly affected is lacking in support, and will almost certainly prove to be wrong, for it must be remembered that the shell is a purely extraneous product, that is to say, it is a secretion of the glands of the oviduct, and has nothing to do with the germ cells, which are alone affected by such crossing. We must pass now to the colours of eggs, or rather, of the shells thereof First of all, let us dismiss certain technical but important facts concerning the composition of these colours. We are indebted for most of what we know of the pigments colouring eggs to the late Dr. H. C. Sorby who by spectrum analysis differentiates seven distinct colours : — 1. Oorhodeine — a very permanent, and very common, red- brown pigment. 2. Oocyan j blue pigments probably closely related, 3. Banded oocyan [ though the second only yields a banded spectrum. 4. Yellow ooxanthine— a bright yellow pigment which, mixed with oocyan gives the beautiful green colour seen in the egg of the Emu. 5. Rufous ooxanthine — a reddish-yellow pigment possibly peculiar to the eggs of the Tin- amous. REPRODUCTION— CONCERNING EGGS 199 6. — a pigment giving a banded spectrum but otherwise little known. 7. Lichen ooxanthine — a brick-red pigment, possibly due to the growth of minute fungi. In some respects we must regard Lichen ooxanthine as the most remarkable of all, that is, if it is really of fungoid origin. This pigment, it seems, occurs in almost all kinds of plants, but especially in lichen and fungi. Dr. Sorby, however, believed that it is a normal constituent of the shell of eggs having a peculiar brick-red colour. Some of the most valuable work in recent years on the nature of the pigments of animals has been done by Miss Newbigin — 'to whom, and to Professor Newton, we are indebted for this summary — but she has apparently not yet investigated the point. The other pigments here mentioned are apparently blood secretions, derivatives of haemoglobin. According to Wickmann they originate from the blood which contributes to the formation of the corpus lutemn, the " yellow body " which is formed by the escape of blood from the capsule in which the egg is formed, after the expulsion of the egg. This " yellow body " appears later to undergo decomposition, or rather a retrogressive meta- morphosis, which results in the formation of pigments. These pigments thus formed within the ovary are shed, according to Wickmann, into the oviduct and mingled with the materials of the shell in its uterine portion, the varying and characteristic hues being due to the difference in the composition of the blood in each particular species. That these pigments are blood-pigments rather than bile- pigments is more than probable, but it is open to question whether they are derived and disposed of in the manner sug- gested by Wickmann ; rather, if they are really derived from the corpus luteuin, it would seem that the products of the meta- morphosis must be absorbed and redeposited in the tissues of the oviduct, where they become set free after the shell has reached a somewhat advanced stage of development; and for the following reasons: " If a bird," says Professor Newton, " bear- ing in its oviduct a fully formed ^^^, be captured, that egg will speedily be laid under any circumstances of inconvenience to which its producer shall be subjected, but such an &^^ is usually 200 A HISTORY OF BIRDS deficient in coloration — fright and over-excitement having ar- rested the natural secretions." Again, in birds which normally lay two richly coloured eggs, it sometimes happens, as in the case of two pairs of eggs of the Golden Eagle, that one egg is colourless. In one instance the coloured, in the other the un- coloured egg was first laid. In the matter of intensity also the colour varies, increasing with age up to the bird's prime and then declining. Finally, if the products of this "yellow body" are simply shed into the oviduct, there to mingle with the grow- ing tissues of the shell, it is difficult to account for the existence of patterns of coloration, as in eggs with zones of colour or streaks, for example, and still more difficult to account for the existence of white eggs, since the "yellow body" will be found in all cases. We may assume then, that however derived, this pigment is deposited by the walls of the oviduct, and it would seem that in many cases this deposition takes place in two different regions of the duct, first on the formation of the earlier layers of the shell, where little more than a slight staining is affected, and later when the shell is nearly complete ; in most cases there is no coloration until the egg has passed some way down the ovi- duct. It would then appear that the ground colour is first de- posited, and after this the peculiar markings of the particular egg. When these are formed while the egg is at rest a sharply defined spot is the result : but it commonly happens that the deposit of pigment takes place while the egg is in motion, smears and blotches being the result ; and it would further appear that the egg in its passage rotates, inasmuch as these streaks and lines show a decided spiral arrangement. These various evi- dences of the process of coloration can be well seen in eggs of many birds of prey, as well as in such strongly marked eggs as those of the Guillemot, for example. When there is a difference in the size of the two ends of the egg, as is commonly the case, the larger appears first, as has been proved by experiment. He would be a bold man who would attempt to describe all the varied hues and patterns which birds' eggs display, and his labour would be lost in the interminable, repellant descriptions in which such an attempt to achieve the impossible would involve him. But two points must necessarily strike any one confronted REPRODUCTION— CONCERNING EGGS 201 with a large and representative collection of eggs. Firstly, that the colours displayed bore no sort of relation to those of the birds which laid them, and secondly, that there was little about these shells that would enable him to decide the particular species, or even genus, to which such and such an egg belonged, rare cases only excepted. At the first blush it may seem curious that since the pigments of egg-shell and of feather are alike derived from the blood, there should be such striking contrast between the colours of a bird and the eggs which it lays. This contrast is rriarked in- deed in such species, for example, as the Hedge-sparrow and the Thrush, whose eggs are blue, yet in the matter of plumage they are the most sober-coloured of birds ; while the gorgeously clad Kingfishers and the Bee-eaters lay milk-white eggs. But the explanation of these things is not far to seek. In the first place, the colours of feathers are often due, not to pigm.ent, but to structure (p. 284). This is never the case with eggs. The wonder- ful iridescent blue of the Kingfisher is a case in point, for the blue colours of the feathers are never due to pigment. In the second place, the coloration of the shell is, on the whole, as much governed by natural selection as are the colours of the feathers of the bird which laid them. To this point we shall return presently. For the moment we must pass to the question of markings of the shell, though there is unfortunately at present little enough that can be said on this head. We have indicated already the process by which these markings are made, and all that can further be said on the subject may now be briefly sum- marised. They range then from minute frecklings, such as are met with in some Game-birds, through sharply defined dots, to blotches and smears, and irregular lines and streaks which sug- gest hieroglyphics of some sort, as in the eggs of Buntings and the Jacanas among the Plovers ; while many eggs are what is called " double-spotted " on account of the fact that many of these spots are but faintly indicated, and evidently deposited in a deeper layer of the shell. In some eggs, as in those of certain Petrels, the pigment is almost, and sometimes entirely, confined to a zone around the larger end. But perhaps the most striking fact about this coloration is the lack of uniformity which pre- vails among even closely allied species, species which in plumage bear an exceedingly close resemblance, while birds in no way 202 A HISTORY OF BIRDS related may lay very similar eggs. Not only indeed do nearly allied species lay eggs of widely different coloration, but instances are numerous where differences no less striking obtain between eggs of the same species, of which the Guillemot affords one of the most striking and familiar instances. And much the same is true of the shapes of eggs. Nevertheless, there are not want- ing Ornithologists who, in the face of these facts, employ the coloration, or lack of it, as a factor in classification ! Contradictory though it may seem, it is yet true, however, that in broad outline we may distinguish the eggs of the larger groups, though, as might be expected, exceptions are fre- quent. Thus, for example, the eggs of the Tinamous are distinguished by their extraordinary burnished appearance, met with nowhere else, except in one or two isolated cases among the Passeres {Bur- nesia), but from which they can of course readily be distinguished by their size. Among the Petrels, such eggs as are coloured have the pigment deposited in the form of a cap, or of a zone around the larger end, though this peculiar distribution is not confined to the eggs of this group. Among' the Steganopodes the Tropic- birds lay richly coloured eggs, those of the remaining families are more or less thickly incrusted with a white chalky deposit concealing, as in the Cormorants and Gannets, a shell of a beauti- ful blue colour. The Anserine birds, without exception, lay whole-coloured, unspotted eggs ; and so also do the Stork tribe, whose eggs are generally blue or green in colour, though in some cases, as in the Ibises and Flamingoes, they are white and chalk incrusted. The eggs of the birds of prey are either wholly white, or have a ground colour of white, bluish-white or cream colour, spotted with red of various shades, and purplish pigment being distributed in the form of blotches varying in number and intensity, so that the colour ranges from a pale rust-red to a rich sienna-red, or inky purple, the blotches being sometimes so thickly clustered as to entirely suppress the paler ground colour. Thus the eggs of birds of this group are often of rare beauty. They also exhibit a marvellous range of variabilit}' in the matter of coloration, those of the Indian Kite {Milvus govinda), for example, in this respect are said by Mr. Hume, whose authority is great, to defy description. While the Game-birds, as a rule, lay whole-coloured eggs, generally cream or buff REPRODUCTION— COxNCERNING EGGS 203 coloured, there arc a few whose eggs are spotted and sometimes double-spotted. The Grouse, Snow-cocks {Tetrnogallus), and Red-legged Partridges lay spotted eggs : so also do the Quails and Hemi- podes — if these last be true Game-birds. The eggs of the Game- birds are noteworthy as presenting a perfect gradation from whole coloured, through minute freckles of pigment to spots, and from spots to blotches. P'urther, in some species they present a really wonderful range of variation, as, for example, in the Australian Swamp Quail, no two clutches being alike either in size or col- oration. Some are white, others cream coloured, and others again sparingly or thickly freckled and blotched with grey, rufous or brown. Occasionally, as in the case of the Chukar Partridge {Caccabis chukar), the coloration varies with the geo- graphical range. Thus eggs taken in Greece are frequently unspotted ; those from the Grecian Archipelago and Cyprus are generally slightly and sometimes boldly spotted ; more to the eastward they are invariably spotted, and frequently blotched with purplish, reddish or yellowish-brown, grey and pink. It is little to the credit of the " field-naturalist " that we have no information as to the nature of the environment of the birds in these different areas. The eggs of the Cranes and Rails are always more or less spotted. In the Rails these spots are usually small and of various shades of Indian red on a cream or white ground. Sharpe's Crake {Snurotlinira iiisiilaris) lays a white egg. In the Cranes the coloration is stronger, forming large spots and blotches of various shades of brown and purple on a dark — occasionally light — ground. Pew hobbies perhaps have engendered more enthusiasm, have called forth more enterprise, pluck and hardihood, than egg-collecting. Yet, it must be confessed, the gain to science^ for all this expenditure, has been pitifully small. The collector has furnished the raw material for the more serious student it is true, but he has made little enough use thereof himself. To his credit at any rate be it said, that he was the first to point out the striking resemblance between the eggs of the Plover tribe and of the Gulls, birds hitherto believed to be quite unrelated. Since then it has been shown, on anatomical grounds, that this resemblance between the eggs is no mere coincidence, but one 204 A HISTORY OF BIRDS of many links in the chain of evidence showing that the two groups are really very intimately related indeed. With the exception of the Jacanas these eggs are all spotted with various shades of brown and black on a groundwork vary- ing in hue from white, cream, brown, to blue and green. The Jacanas are remarkable. The Pheasant-tailed Jacana {Hydro- pJiasianus chirurgiis) is the only species of the group which lays a white egg ; while the remainder have the shell covered with in- extricably twisted lines forming a sort of tangled meshwork all over the o.^'g. But in the matter of variability none can compare with the eggs of the Guillemot ( Uria troile), which are often of extreme beauty. No less than thirty well-marked variations of these eggs are exhibited in a special show-case at the British Museum of Natural History. The great range in pigmentation is really wonderful, but still more wonderful is the variability of the size and distribution and shape of the markings. No mere description could do justice to these eggs ; suffice it to say in the ground colour they may be white, blue, green, brown, yellow, buff or pink, while the markings consist of blotches, spots, streaks and lines of every conceivable shape, and ranging in colour through different shades of brown, reddish, choco- late, and black ; while some eggs have scarcely any markings at all, others have the surface of the shell thickly covered. But there can be no doubt but that, as in other cases, the eggs laid in successive seasons by each individual are always of the same type, i.e., a Guillemot which lays a green or a red egg for the first time of laying, will produce eggs of the same type in successive years so long as it lives. The significance of such extreme variability is far from ap- parent, but it has been suggested that this individuality is the outcome of selection, the end gained being to enable each bird in the colony — for these are social birds — to recognise its own The remarkable pyriform shape of the Guillemot's egg we have already referred to ; the Lapwing and many other Plovers lay eggs of a similar shape. On the other hand, no inconsider- able number lay eggs of the more typical form. Even among birds of the same genus and even of the same species great differences in this respect obtain. Among the Snipe many REPRODUCTION— CONCERNING EGGS 205 instances of this occur ; thus the eggs of the Common Snipe are usually pyriform, but examples of an oval shape are common ; the eggs of the Himalayan Solitary Snipe {Gallinago solitarid) are extremely pointed in shape, while those of Strick- land's Snipe {G. stTicklandi) are remarkably long, narrow and blunt-pointed. As a rule where these markedly pyriform eggs occur they are laid four in a clutch, and with the narrow ends turned inwards, thus economising space, or what is more to the point, arc more perfectly covered by the sitting bird. Thus it would be of great interest if observations could be kept on such nests of the Common Snipe as are found containing the less specialised type of eggs with a view to discover whether incubation is in any way affected thereby. We may bring this survey to a close with a {q.\n comments on the eggs of that great assemblage of forms which has been aptly grouped under the collective term " Pico-passeres ". It is interesting to note here that while among the " Picarian '' or " Coraciiform " types white eggs are the rule, among the Passerines such are very rare, e.g., Dipper, Sand and House Martin. As touching the significance of this lack of colour we shall speak elsewhere (p. 207). Although many thousands of species are included in this great brigade — the Passeres which includes more than half of all the known species of the Class Aves — it is a somewhat remarkable fact that in so far as their eggs are concerned, they present a wonderful uniformity. True, indeed, they present variety enough in their colora- tion, which is often of great beauty, but eggs precisely alike are laid by species not even remotely related. Where markings are present they take the form for the most part of small spots and freckles, such, for example, as in typical eggs of our Common Thrush or of the Blackbird ; or the pigment may be deposited in the form of a cap or of a band, or yet again in hair-like irregular lines, as in the Buntings. As among species outside the assemblage now under dis- cussion, the eggs of some of these " Pico-passeres" are subject to remarkable ranges of variation. In the case of the Common Cuckoo this variation has a definite and peculiar significance, but this is certainly not apparent in such cases as are met with, for example, in our Common Blackbird {Tiwdus inerula) 2o6 A HISTORY OF BIRDS or some of the Babbling Thrushes, e._i^., Alcippe nipalensis, though numerous instances of such variations could be quoted. The eggs of the Black-cap {Sylvia atricapilla) again, in common with many other species, exhibit three distinct types : in one the ground colour is greyish-white or grey smudged and mottled with brown and lavender ; in another the ground colour is salmon-pink smudged with darker pink and grey, and spotted with reddish-brown ; while in the third type the shell is white, blotched and speckled with chestnut and lavender. Not even a plausible explanation of this variability has yet been found. All three types may occur in the same locality, and they are not correlated in this or any other cases — and they are numer- ous — either with peculiarities of plumage or of the construction of the nest or of its site. Yet, generally speaking, the coloration of eggs has a real significance, inasmuch as it is undoubtedly determined to a large extent by the nature of the environment. That is to say, the coloration can be shown to be protective in a very large number of instances. Nowhere is this more certainly true than in the case of such eggs as are deposited on the ground and left for longer or shorter periods completely ex- posed. The eggs of the Plover and Gull tribe constitute the most striking examples of this fact, as those who have tried to find them know well. The eggs of the Marsh-dwellers, since they deposit their treasures on dark, damp ground, have the ground colour of the shell of some dark hue, with darker blotches and spots, while among such as nest on sandy or shingly beaches the ground colour of the shell is correspond- ingly pale, with similar dark markings, and so perfectly do these frail bodies match their surroundings that they are discovered by accident rather than design ; even expert egg-collectors are reduced to adopting various devices to aid them in their search. Thus then the curious dissimilarity, the unlikeness which obtains between the coloration of the eggs and of the bird which lays them, becomes no longer a matter for wonderment ; in both instances they are the outcome of the needs of the environment, of mechanical selection. Both eggs and birds have enemies, and the device — if " device " it may be called — of protective coloration is one of several ways for circumvent- ing these enemies. As the size and shape and relation to the REPRODUCTION— CONCERNING EGGS 207 ground of the two bodies — egg and bird — differ, so each de- mands a special kind of coloration, where this serves. With a strange perversity, many who have discussed this question seem to find insuperable difficulties in explaining the lack of protective coloration which obtains in the great majority of coloured eggs. But in such cases, almost without exception, these eggs are deposited in a nest, itself not infrequently a a conspicuous object. This being so, protective coloration avails nothing for the eggs. Where protection for these has become necessary it is the nest which has undergone the neces- sary transformation (p. 179). Yet the question naturally arises as to why such eggs are coloured. If the pigmentation of the shell neither confers protection nor courts destruction, it would certainly almost seem as though it should, in such cases, have disappeared as a result of the cessation of selection. But this by no means follows, since these varied hues may serve other purposes, where they are not actually protective. On the other hand, the coloration may represent a more or less modified form of an earlier protective type, white eggs being due to the action of selection ; and on this last point we have sure evi- dence. But to appreciate this, it is necessary that the broad outlines of the evolution of coloured eggs should first be traced. It is almost certain that the eggs of the earliest birds were white, like those of their forebears, the reptiles ; and further since these primitive birds were arboreal, that they were laid in holes of trees or under other cover. Later, when some migrated from the forest region to the plains or meadows colour became necessary : firstly, for protective purposes, and secondly, probably, as a defence against the action of light, which in excess is inimical to protoplasm. It is not really difficult to see how the varied coloration seen in birds' egfcrs to-day may have been evolved, and in all probability egg-eating animals largely aided its development. We may assume that, as in the case of the Sphenodon or Tuatera Lizard of to-day, there was a tendency to develop rust-coloured stains on the shell, some eggs being more decidedly marked in this way than others. Now with the migration to exposed localities, these eggs, unless constantly brooded by one of the parents, would have to remain exposed for longer or shorter periods, when sooner or later various creatures in the new environment would 208 A HISTORY OF BIRDS make the discovery that these white, hard bodies contained very kiscious meat, and with this discovery the work of selec- tion would begin. White eggs, at the beginning of this process of weeding out, would be the dominant type. Consequently, the taste for white eggs would be the first to be acquired, and their enemies would pass coloured so long as white eggs were to be had ; and so, in course of time, the birds which laid these would die, and die without leaving offspring; while those which produced blotched and spotted eggs would produce more vigorous off- spring because they would escape the constant strain of laying a large number of eggs in each season, and year after year, to replace the loss by robbery. Such offspring would, in turn, inherit the tendency from their parents, lay more and more strongly coloured eggs, which more and more would tend to resemble their environment, or, in other words, would become protectively coloured. And now we come to the problem of the significance of the white eggs met with to-day. If the foregoing arguments are sound, then few birds laying white eggs could maintain a hold on life as a species, save those which deposited their eggs in holes or burrows. The exception to this sweeping rule shall be considered presently. Among these troglodytes then, selection has been at work eliminating any but white eggs, since colour, rendering them invisible in the dark, would tend to their de- struction by the sitting bird when entering the nest. Thus then white eggs are as much the result of selection as coloured. Birds, in short, lay white eggs to-day because they lay them in holes. In a large number of birds, in all proba- bility, none but white eggs have ever been laid since their race began, while in other cases, as we shall see, this whiteness has been secondarily or re-acquired. This view, however, is quite at variance with that generally adopted, which was first pro- pounded by Dr. Alfred Russel Wallace. This being so, it would be well to state his views. He contends then that birds whose eggs are white resort to holes wherein to hide them. Such, for example, are the Petrels, Kingfishers, Bee-eaters, Parrots, Woodpeckers, Hornbills, Hoopes, Trogons and Owls. But surely the more reasonable interpretation of this rule is exactly the opposite of that suggested by Wallace. That is to REPRODUCTION— CONCERNING EGGS 209 say, that birds lay white eggs because they lay them in holes, inasmuch as in such dimly lighted places coloured eggs, from their lower refracti\e power, would run grave risks of being broken whenever the bird entered the nest, while white eggs, in this dim religious light, are just visible. For a somewhat similar reason plants that are fertilised by night-feeding insects have white flowers, white being conspicuous in the dark, whilst colour is invisible. We ourselves adopt a similar expedient for making objects conspicuous in dark places. Thus in the dark corridors of the British Museum of Natural History a piece of white paper is pasted around the keyholes of doors to serve as a guide there- to, while on underground railways the edges of the platforms and the stairs leading thereto are similarly painted white. By way of supporting this hypothesis as to the significance of white eggs, we may cite the case of the British Puffin whose eggs are white, and deposited in burrows. But if these eggs be examined they will be found to be but thinly covered with a layer of white over a coloured surface, recalling that of the eggs of the Guillemot and Razor-bill. Here then it would seem the custom of laying in burrows is of recent origin, and that selection has begun the work of suppressing the colour, and we may therefore assume, with some justification, that the white eggs of other hole-breeders have similarly acquired a secondary colourlessness, or in other words, have re-acquired the primitive white colour: or it may be that this has been brought about not as in the Puffin but by reversion, though in the majority of cases, as vi^e have already suggested, this development of colour may never have taken place since the race began. But some birds, it may be objected, whose eggs are remark- able for the richness and beauty of their coloration, yet lay them in holes. The Snow-bunting {PlectropJianes nivalis) would appear to be a case in point. When, however, we come to examine this, we find that though such nesting sites are used in Scotland, in the tundra of Siberia they deposit their eggs on the ground, concealed amid tussocks of grass. Thus the breeding habit of Scotch birds is exceptional, and determined by the nature of the environment. It may well happen that in course of time those which persist in breeding in holes will come to lay white eggs like the Puffin. Another objection which may be raised is that many birds, as the Pigeons, for example, lay white eggs 14 210 A HISTORY OF BIRDS in open nests. According to some oologists this is a protective device, the structure of the nest being of so loose a character that the light can be seen through when viewed from below, and the white eggs are mistaken for light patches. This is a far- fetched explanation. Such creatures as may prey on these eggs must be able to gain access to the nest from above, whence the eggs would be conspicuous enough. Probably the surround- ing leaves of the overhanging boughs afford protection enough from such enemies, or they are not sufficiently numerous to be seriously harmful, for it must be remembered that even pro- tective coloration is not an absolute protection. Finally, it is a matter for comment that there are no black- shelled eggs, inasmuch as black frequently occurs in the form of spots. As touching the structure and composition of the egg we need say but little here, yet a few words on this subject are necessary. To begin with, what is popularly called the egg is this, and something more. What is this " something more," and what is this egg? If, say, a hen's egg be carefully broken into a cup there will be found a large yellow mass, surrounded by a clear jelly-like elastic coat. On the top of the yellow yolk, in the centre of the field, there will be noticed a small white spot. This represents the germinal protoplasm destined to form the chick ; the cushion on which it rests constitutes an enormous food store which is gradually absorbed as the development of the chick proceeds. The eggs of the lower forms of life, as is pointed out in vol. iv. of this series, though extremely minute in size, consist of a similar mass of germinal protoplasm, including only a very small quantity of food yolk. Hence the developing organism is thrown upon the world in an extremely undeveloped condition, bearing no sort of resemblance to the adult form. Owing to the scanty supply of food material with which it is provided, the microscopic creature has to obtain its food from the surrounding medium, hence it begins life as an aquatic animal or " larva," though it does not always necessarily remain there. But to return to our point — the egg in the cup. The cushion of yolk to which we referred is enclosed by an extremely thin and delicate skin, the vitelline membrane, while the yolk within, if examined in a section of a hard-boiled egg, will show that it is not REPRODUCTION— CONCERNING EGGS 211 of uniform structure throui^hout, but that there is a portion of it having the shape of a flask with a funnel-shaped neck, and containing;' a quantity of more or less fluid matter. The ex- panded neck of this flask-shaped space is situated immediately under the small white spot or disc, while its bulbous portion extends to the middle of the egg. The fluid contents of this flask are known as the " white yolk," and similar white yolk will be found throughout the rest of the yellow yolk, disposed in the form of concentric layers enclosing yellow yolk between them, the final layer lying immediately under the vitelline membrane, and becoming continuous with the expanded neck of the flask just described. The " white yolk " differs, as might be expected, from the yellow yoke in its microscopic characters, but into these differences we need not enter. The clear jelly-like outer investment of the yellow yolk con- stitutes the " albumen " of the egg, and from its appearance when boiled is known as the "white" of the egg. If carefully examined in the unboiled egg there will be found at each pole, embedded within this albumen and extending from the vitel- line membrane, a little spirally twisted "cord" of denser struc- ture, that at the narrow end of the egg being more or less firmly fixed to the shell, or rather to the membrane lining this. These bodies serve to keep the yolk in position, as well as the purpose of pads to reduce the effect of shock. From the fact that the interior of these cords presents the appearance of a succession of white knots, these cords are known as " chalaz^ " (hailstones). If an opening be cut through the side of the shell of a fresh egg, the germinal portion will always be found at the top. This is due to the lighter specific gravity of the yolk in the neigh- bourhood of the disc, and not to the control of the chalazae. In birds the left ovary alone is functional. Each egg is en- closed in a capsule, and on the completion of its store of yolk, that is to say when ripe, bursts its capsule and escapes into the oviduct, and here the completion of its growth commences. This consists in the addition of the albumen and the shell membranes and the shell, which are formed by the glands of the walls of the oviduct. The true egg then consists only of the germinal protoplasm and the yolk, since these only are produced by the ovary. The 212 A HISTORY OF BIRDS white and the shell are accessory structures, though it is to be noted the former is finally absorbed by the developing chick. These accessory portions — the albumen, shell membrane and shell — are added in the lower part of the oviduct, the mem- brane lining the shell being formed by the transformation of the outermost layer of albumen, while the shell itself is formed by the secretion of a thick white fluid, in which, finall)', the pig- ment, when this is present, is mingled. The albumen and the shell membrane are formed in about three hours, while the completion of the shell takes about eighteen hours. With regard to the membrane adherent to the shell we may remark that this is double, and that at the larger end of the egg the two layers part company, the space between being filled with air drawn in through the porous shell. As incubation pro- ceeds this space grows larger, and thus the necessary supply of oxygen for the developing chick is obtained. Such then is the answer to the questions, what is an egg ? and what is this " something more " ? The fertilisation of the egg takes place immediately after its escape from the capsule in which it was developed, into the oviduct ; so soon as this is effected the early stages of develop- ment begin, but these cease so soon as the egg is laid and be- comes cold, to be resumed again by the brooding of the parent. CHAPTER XIII REPRODUCTION {continued)— CAKE OF THE OFFSPRING Brooding and " brood-spots ". Care for the sitting female. The remarkable case of the Horn-bill. The brooding of the Emperor Penguin. Brooding of Egyptian Plover and of Megapodes. Forsaking eggs. Osprey and care of eo-crs. Transportation of eggs by parents. Precautions against floods. AT first sight it may seem that the jealous care which birds bestow on their offspring originated with the necessity for brooding the eggs. But this is clearly not the case, since among the invertebrates there are numerous in- stances to be found where a high degree of concern appears to be bestowed upon the eggs and young to ensure their safety, and these instances become more numerous as we pass in our sur- vey to the lower vertebrates. With the birds and mammals, however, this care develops into something higher, entailing personal sacrifice in a high degree, so much so that we should perhaps rather speak of the love for their offspring which these creatures exhibit, though there are some striking exceptions to this rule. With the birds the cares of the family begin at an earlier stage than with the mammals, inasmuch as it commences with the brooding of the eggs, while the mammals, being viviparous, are necessarily relieved of this responsibility until after the birth of the young. To this necessity for brooding the eggs we may ascribe the relative fewness of the young produced at a time, as compared with the reptiles, since no more eggs can be hatched than can be effectually covered by the sitting parent. Among the mammals but little preparation, as a rule, is necessary for the reception of the young. And this is true of many birds : in the majority of cases, however, a more or less elaborate receptacle, or nest, has to be constructed to contain the eggs during the process of hatching (see p. 176). 213 214 A HISTORY OF BIRDS It would seem that the " field-naturalists " as a general rule — for there are notable exceptions — find more pleasure in nest- robbing than in nest-watching ; for though they have been as- siduous in recording the number of eggs in a clutch, variations in colour and size, and in the choice of nesting site, their contri- butions towards our knowledge of the brooding habits of birds are singularly (ew and miserably incomplete. The early stages of the development of the chick begins within the body of the parent, but all further growth is sus- pended directly the egg is laid, to start afresh with the brood- ing of the parent. While in the majority of birds this does not begin until the whole complement of eggs has been laid, in some cases incubation begins with the first egg, as among the diurnal birds of prey and the Owl, for example, so that the late eggs are partly incubated by the earlier hatched nestlings. Monogamous species would appear generally to share the duties of incubation, as may be seen by the bare and somewhat inflamed area of the abdominal wall of the body of the sitting bird due to the increased flow of blood to this area, whereby the necessary warmth for the developing chick is supplied. But a careful analysis of the species in which this division of labour obtains is yet wanting. In many cases, however, the work of incubation is performed by the hen only, who, forsaken by her mate, sits assiduously, leaving her charge only at distant intervals for the purpose of procuring food and for defecation. This last act is performed as far as possible away from the nest, and is delayed until the cloaca becomes unable to bear further strain. With some species, however, the hen is constantly sup- plied with food at this time by her mate. In the case of Montagu's Harrier, for example, the cock so waits upon the hen. At his approach with food she flies out to meet him, whereupon he drops his spoils, to be caught by her in mid- air and borne back to the neighbourhood of the nest to be devoured. The little Red-backed Shrike is most attentive at this time, feeding her as she sits upon her nest. Similarly, the female Blue-tit, and indeed quite a number of species, are fed, when sitting, by the male. Where both parents sit, how- ever, no feeding appears to be done, each providing for itself when released from the cares of incubation. The hen Hoopoe, save when moved by necessity, does not stir from the nest REPRODUCTION— CARE OF THE OFFSPRING 215 during the whole period of incubation, during which time she is fed by the cock. In the nearly allied Hornbills this peculiar division of labour reaches a very remarkable and unique climax. Among these birds — there are several species — but a single egg is laid, and this is deposited within a hollow tree. Directly afterwards the male proceeds to close up the entrance to the nest, leaving but a narrow slit ; but except for this aper- ture, through which she thrusts her bill to receive the food brought by her indefatigable mate, there is no communication with the outer world. She is a prisoner, we presume volun- tarily, until the egg is hatched ! The substance used in this walling-in operation would seem to differ among different species, varying doubtless according to the materials available in the different parts of the breeding range. Dr. Hose, a keen naturalist, and for many years one of the resident magistrates of Sarawak, carefully examined the plaster used by the Rhin- oceros-hornbill (Buceros rhinocct'os), and found it composed of a substance resembling vegetable resin — probably a salivary secretion — mixed with the woody fragments of fruit. Some species appear to use the undigested skeletons of centipedes in addition. During her period of solitary confinement, as we have re- marked, she is assiduously fed by her mate. And thereby hangs a tale, as wonderful as anything in nature — wonderful because her daily rations are passed to her in the form of a bolus, the investing coat being furnished by the inner lining of the gizzard of the male ! At least this is the commonly ac- cepted explanation of the structure of this capsule, though it is probable that it may prove to be formed by a special glandu- lar secretion when the matter is further investigated. This is the more likely interpretation, because, according to other ac- counts, each meal is divided into from two to four pellets — containing fruit, seeds, insects and portions of reptiles— which the devoted cock transfers into the gaping mouth of his fair prisoner by a series of jerks. No wonder that by the time the egg is hatched she has become a " mass of fat," while he is reduced to a mere skeleton, so lowered in vitality that on a sudden fall in the temperature, such as takes place after rain, he not seldom falls down exhausted and dies ! Speaking broadly, the hens alone sit among the Game-birds, 2i6 A HISTORY OF BIRDS Ducks, Birds of Prey, Storks, Cranes, Rails and Wading birds, and probably in many other cases, concerning which, however, we appear to have no records — while in a few cases, as in the Cassowary, Rhea, Tinamous, Painted Snipe, Hemipodes and Phalaropes, the whole work of incubation is performed by the male alone. There are, of course, exceptions to the rule; thus, among the birds of prey the female only incubates in the case of the Harriers, both parents in that of the Buzzards. Among the Sand -grouse the hen broods by day, the cock by night. Where the hen alone sits the males, as in the Ducks, for example, betake themselves off to some distant spot to return on the hatching of the young ; in other cases, as among the birds of prey, the cock remains near at hand to protect his mate and home. There are two species of birds which enjoy a unique dis- tinction in the matter of brooding. These are the King and Emperor Penguins. Laying but a single egg, this is most tenderly nursed by both parents alternately, and on the back of the feet. That is to say, the egg, instead of resting on the ground, is supported on the upper surface of the feet, where, pressed close to the body, it is covered by the loose skin of the abdomen and the feathers. Dr. A. E. Wilson, one of the naturalists of the Discovery expedition to the Antarctic during 1901-1904, made a most careful study of the nursing habits of these wonderful birds. A most shrewd and accurate observer, his vivid account of the terrible struggle of these birds to maintain a hold on life will ever remain a model as to how and what to observe in studying the life-histories of animals, and will be the more impressive because of the unusual difficulties and hardships attending these observations. While the bulk of the work would appear to fall on the hen, the cock, as we have hinted, bears his share. But the work of transferring the precious egg is evidently regarded by these fond parents as one of no small importance and delicacy. Consequently a certain amount of ceremonial attends the transfer. The cock, when about to relieve guard, approaches his mate, when both bow one t6 another. He then proceeds to inspect the egg before taking it over, and having satisfied himself that all is in order, assumes charge of the burden. In spite of Dr. Wilson's en- deavours, however, he never succeeded in witnessing the method REPRODUCTION— CARE OE THE OFESFRING 217 by which the transfer was effected. Six lonely weeks, in darkness of mid-winter, are thus passed before the chick appears, bringing with it increased cares and responsibilities (p. 287). Dr. Wilson exploded one curious myth concerning the brooding habits of the King Penguins, a myth all the more remarkable because created by a naturalist of no less standing than the late Professor Moseley. He it was who, in his account of the Voyage of the Challenger — which he accompanied in its now famous journey round the world in the capacity of naturalist — stated that the King Penguin carried its egg in a pouch between its legs. It is strange that the probability of his having been mistaken as to the pouch should not have occurred to him, and that he should not have inquired further into the matter, by way at any rate of comparing this with that of the marsupial Mammalia. While incubation among the birds is almost universally performed by brooding, there are one or two noteworthy ex- ceptions to this rule. Thus the little Egyptian Plover {ALgyptius pluvialis) buries its eggs in the sand, brooding them only during the chill hours of night. The Ostrich has been said to adopt a similar device for escaping the irksome work of brooding. As a matter of fact, however, the hen broods by day and the cock by night ; but during wet weather, be it noted, the cock sits by day as well as by night, while in the more tropical parts of its breeding range the eggs are said to be left during the day to the sun's rays, covered only by a layer of sand. But the Mega- podes have utterly abandoned all brooding habits, and leave their eggs entirely to natural agencies to hatch, the methods by which this is accomplished varying with the different species. Thus the " Maleo " {Megacephaluni maleo) of Celebes " come down in pairs," says Wallace, from the interior to the beach, where they " scratch holes in the coarse black volcanic sand three or four feet deep and four to five feet wide, just above high- water mark," therein an egg is laid, then covered with about a foot of sand. At the end of ten or twelve days the journey is repeated, and so on until from six to eight eggs have been buried within this pit. Not seldom, however, several birds continue to lay in the same hole, as many as a dozen eggs having been found together. After the last eggs are laid the birds return no more, and the young, on hatching, work their way up through the 2i8 A HISTORY OF BIRDS sand and run off at once into the forest. Wallace's Megapode {Megapodiiis luallacei), which inhabits Gilolo, Ternate and Bourou, has similar nesting habits, and so also have Brenchley's Megapode {Megapodius brenchleyi) of '^ew Britain and Solomon Islands, and Pritchard's Megapode {M. pritchardi) of Hope Island. It would seem, however, that in Celebes the Maleo occasionally breeds inland, and in this case the birds seek out, in the highlands of the island and in the forest regions, spots in the immediate neighbourhood of hot springs, thereby finding compensation for the lack of the sun's rays. Yet other species adopt different methods. The Australian Brush-turkey, for instance, lays its egg in a mound of decay- ing and fermenting vegetable matter. Two or more females commonly combine, scraping together by means of their enormous and powerful feet a mass of twigs and rotten leaves and other debris, till a heap is raised as much as six feet high and twelve or fourteen yards in diameter at the base. The rotten leaves and fine materials are placed in the centre, while the outside is composed of sticks, leaves and twigs recently gathered. The heap made, the birds dig down deep into the centre and there deposit their eggs, in the fine leaf mould. From examination of these mounds it would seem that the eggs are laid with the pointed ends downwards, often in a circle, with three or four in the centre, about six inches apart. As many as thirty-six eggs have been taken from a mound of this description. The mound of the Dark-billed Brush-turkey {Talegallus fiiscirostris) of Southern New Guinea has been described by Von Rosenberg. It is, he says, " composed of earth, mixed with sticks and leaves, the whole forming a truncate cone eleven feet high and twenty-five feet round the base. In the summit of the cone we found the openings of five burrows which went down per- pendicularly to a depth of four feet, and were filled with earth. In four of these I found eggs which were placed vertically . . . and were in various stages of development. In the mound the thermometer rose to 93° Fahr., while the surrounding atmo- sphere was only 85° in the shade." Of Duperry's Megapode the traveller-naturalist Gilbert writes of a visit to Knocker's Bay in search of this bird : " I suddenly found myself beside a mound of gigantic proportions. It was fifteen feet in height and sixty in circumference at the base, the upper part being about a third REPRODUCTION— CARE OF THE OFFSPRING 219 less, and was entirely composed of the richest description of light vegetable mould : on the top were very recent marks of the birds' feet. The native and myself . . . after an hour's work . . . succeeded in obtaining an egg from a depth of about five feet ; it was in a perpendicular position, with the earth very lightly touching it on all sides, and without any other material to impart warmth, which indeed did not appear neces- sary, the mound being quite warm to the hands. The holes in this mound commenced at the outer edge of the summit, and ran obliquely towards the centre : their direction there- fore is not uniform. Like the majority of mounds I have seen this was so thickly enveloped in foliaged trees as to preclude the possibility of the sun's rays reaching any part of it. . . . The mounds are doubtless the work of many years, and of many birds in succession : some of them are evidently very ancient, trees being often seen growing from their sides : in one instance I found a tree growing from the middle of a mound which was a foot in diameter. . . . The natives say that only a single pair of birds are ever found at one mound at a time. . . . They also affirm that the eggs are deposited at night, at intervals of several days." Concerning the significance of this remarkable habit of incubation we have elsewhere commented (p. 248), but we may remark here that the vertical position of the egg is somewhat curious. All who have examined such mounds agree in that this is the universal position of these eggs, and interesting testimony of the accuracy of these observations was obtained during 1904 at the Zoological Gardens in London, where a pair of Brush-turkeys {Talegalla lathami) built a perfectly typical mound, and from which in due time young emerged. From observations made on this mound, it seems probable that the young do not force their way until about thirty-six hours after hatching, the chicks remaining within the shattered shell until sufficiently strong to make the necessary efforts to escape from this living tomb. Either the dread of man is much greater in some birds than others, or they have less of that mysterious love for their off- spring which, in some birds, as among the human species^ amounts to an overmastering passion. For while some species forsake their eggs on the slightest of pretexts afforded them by 220 A HISTORY OF BIRDS their ancient enemy, others appear to set all danger at defiance to save these precious pledges of joys to come. Thus while some species will leave their eggs, when necessity demands, fully exposed, trusting apparently to their protective coloration when this exists, others carefully conceal them, covering them, as in the case of the Grebes, with decaying vegetable matter, or burying them in the sand, as with the little Egyptian Plover. In this latter instance it does not appear to be certainly known whether the eggs are buried in the hot sand to save, or at least reduce the work of incubation, or whether they are normally incubated, and covered only when danger compels the sitting bird to seek safety in flight. But among the Ducks this regard appears to reach its maximum, inasmuch as the mother plucks the down from her breast to form both a lining for the nest and a covering for the eggs during her enforced absences. The Eider-duck, if suddenly alarmed when sitting, will instantly leave her eggs, but before doing so discharges over them a quantity of fluid excrement having a peculiarly offen- sive smell, which probably contributes in no small degree to disgust intending robbers. Though this discharge is probably involuntary, it forms nevertheless a device which must be of no little service in the preservation of the species. The Osprey again {Pandion kalicetus) appears to regard her eggs with great solicitude, inasmuch as she has apparently a habit of leaving them exposed for a few hours daily to the sun while she basks therein on a neighbouring branch, ever and anon rousing herself to take a plunge into the lake below, rising therefrom to shake her dripping plumage over the Ospreys that are to be. Here then we have the rudiments of that instinct for the preservation of the eggs of which so many wonderful instances have been recorded. Thus, for example, a case is on record of a pair of Merlins which transported their eggs from a nest in a tree to a bank forty yards distant where they improvised a nest of leaves for their reception ; and this because the sitting bird had been repeatedly shot at while on the nest — to the shame of the shooter, be it said. It must, however, be recorded to the credit of tho.se who instigated this attempted murder, that the birds were allowed to hatch off their young in safety. No less re- REPRODUCTION— CARE OF THE OFFSPRING 221 markablc is the case of a Common Partridge, which was dis- covered sitting on a nest of eggs in a field that w^as being ploughed. The bird was first noticed as the horses passed it, so near that it narrowly escaped being crushed. The owner of the field, who happened to be i)a}'ing a \isit of inspection, quite accidentally descried the bird immediately the plough had pas.sed, and found that she was sitting on a nest of twenty-one eggs, near the point of hatching, for .some were beginning to chip. Returning with the plough, to his surprise he found the nest empty ; and after careful search, suspecting that she must in the meanwhile have removed her eggs, he found them under the hedge about forty yards off; a task which, probably with the assistance of the cock, had been performed in about twenty minutes ! A similar case is recorded by the naturalist Selby of a Moor-hen which had built a nest on the edge of an orna- mental pond, into which the water from another pond was occasionally admitted. This was done while the bird was sitting ; and as the nest had been built while the water level was low the sudden influx caused a rise of several inches, threatening the .speedy submersion of nest and eggs. This the birds apparently realised, for when a gardener who knew of the nest went to it, expecting to find it destroyed, he found the birds adding fresh material thereto by way of raising it above the level of the flood, and further search revealed the eggs, which had been deposited on the grass a foot or so from the water's edge. Fearing that he might alarm the birds, he did not remain to watch their further proceedings ; but return- ing in less than an hour found the hen comfortably sitting on the newly raised nest. A few days afterwards the young were successfully hatched. A similar case has been recorded of a Swan which, while sitting on a nest of four or five eggs, was observed to be " very busy collecting weeds and grasses to raise her nest. A farm- ing man was ordered to take down half a load of haulm, with which she most industriously raised her nest and eggs two feet and a half. That very night there came down a tremendous fall of rain, which flooded all the malt-shops and did great damage. Man made no preparation, the bird did ; instinct prevailed over reason. Her eggs were above, and only just above the water." 222 A HISTORY OF BIRDS It must not be supposed that the number of such instances ire confined to those here recorded. Romanes has brought together many similar cases, some of which refer to cage-birds, but sufficient have surely been mentioned here to show how great is the love of some birds for their as yet unborn young. chaptp:r XIV CARE OF OFFSPRING {coufumcd) The care of the young undertaken by the male alone, and by the female alone, or by both parents. The remarkable case of the Sand-grouse in procuring water for their young. The strange case of the transportation of the young in the Woodcock. Feeding customs. Sanitation of the nest. The callousness of Eagles. The coloration of nestlings. WITH the hatching of the eggs and the advent of the young the cares and labours of the parents enter a new and more exacting phase. Where the female has been left to carry out the work of incubation alone she is now often joined by her mate, no longer able to ignore his responsibilities, or perhaps roused into activity by the sight of his offspring. In some cases, however, the hen has to shield her young from the vicious onslaughts of the cock, who, however, soon appears to accept the inevitable and settles down to aid in the work of feeding. In the Emu {Droincens), on the contrary, the reverse is the fact, but here, it must be remembered, the duties of incubation and the care of the young devolve entirely on the male. But where the cock takes the task of incubation entirely upon himself the maternal instincts seem to be de- generate, inasmuch as the care of the young, as of the eggs, devolves entirely upon him, as, for instance, in the case of the Rhea and the Emu. By way of contrast, we find that among the Pelicans and the Ducks, for example, the care of the family falls on the female only. But the arduousness of parental cares varies not so much in proportion to the number of offspring as in relation to the condition of this offspring at hatching. Thus young Ostriches, Game-birds or Ducks, which are able to run about almost immediately they leave the &gg, also feed themselves under the parents' guidance ; while young Thrushes, Rooks or Pigeons, for example, are what we may call prematurely hatched (p. 246), 223 224 A HISTORY OF BIRDS and for a long while are utterly unable to leave the nest or to feed themselves. It is curious that while parental responsibilities of a com- plex character are undertaken even among the lowest inverte- brates, the practice of feeding the young obtains only with the ants and bees among the invertebrates, and is not met with again till we come to the birds and the Mammalia. The labour entailed in this among the birds varies with the nature of the food required and its preparation. The active young of graminivorous birds, such as the Game-birds for in- stance, or of the Plover tribe, which feed upon small crustacea, snails, worms and so on, or of the Duck tribe, which live upon vegetable matter and small animal organisms, follow their parents to feed under their direction. But where, as in the case of the Grebes, for example, the food is obtained only by chase, and for the most part by diving, the young swim out after the parents, and are fed by them on a diet consisting of very small fish, crustacea and a small quantity of vegetable matter. The Dabchick or, Little Grebe {T acJiybaptes fliiviatilis), how- ever, appears to differ from its larger relative in this matter, in that the young remain for many hours daily in the nest perched on the back of the mother and covered by her wings, and during this time are assiduously fed by the male, who has been seen to make as many as forty journeys with food in the space of a little less than an hour. Later, as the young gather strength, they are fed on the water, the diet being at least partly vegetable. The food appears to be dropped on the water and picked by the youngsters. The Sand-grouse afford perhaps one of the most remarkable instances yet discovered of the care displayed by birds for their offspring. These birds are dwellers in arid deserts and consequently have to make long journeys night and morning to procure water. During the time that the young are helpless their drinking water is supplied by the cock, and this in an absolutely unique fashion. After having slaked his thirst at the customary drinking pool, generally many miles distant from the feeding ground and young, he proceeds to wallow in the water after the fashion of a bird dusting its plumage, remaining until the feathers of the under parts are thoroughly saturated. LAPWING SETTLING DOWN ON ITS EGGS NOTE THE I.OVVEREi:) CREST FEATHERS WHITE THROAT FEEDING ITS YOUNG CARE OF OFFSPRING 225 As soon as this end is attained he makes all speed back again, when he calls loudly to the young who run to meet him. As soon as he alights they thrust their heads amongst the breast feathers and under tail coverts, and drawing them through their beaks suck out' the water they contain, moving to fresh places as the supply becomes exhausted ! This most interesting discovery we owe to the observations of Mr. Meade Waldo. Whether the young in some way communicate their desire to drink to the parents, or whether they observe signs of thirst in the young, is of course a matter which cannot be determined. No less extraordinary is the case of the Woodcock which frequently nests on high ground at some considerable distance from the marshy swamps where alone food is procurable. When this is the case, the parents carry the young down, at dusk, from the high ground to the swamp, and bear them back again at dawn, carrying them held between the legs. St. John in his Highland Sports refers to this fact, and Dr. F. D. God man, an Ornithologist of wide experience, has described the same habit to me in the case of Woodcocks nesting in the Azores. But this appears to be the only known instance among birds where the young are periodically carried from place to place. Where the young remain long in a helpless state in the nest the work of feeding is increased tenfold, entailing as it does long and frequent forage for food. Nor is the physical strain less when this food is elaborated within the crop of the parent and conveyed to the young by a process of regurgitation. Family cares weigh heavily upon all birds, but heaviest upon those whose young are helpless. To feed them the fond parents must rise early and work late : their toil is incessant. A pair of Blue Titmice have been observed, for example, to make no less than 475 journeys to the nest in the space of seventeen hours. Even Sparrows, for whom little good can be said, at this time excite our admiration on account of their devotion to their young. While daylight lasts indeed they can know but little rest, for the insatiable appetites of their callow brood keep them almost ceaselessly at work. During the first few days, as with other Finches, they feed their brood on insects, many of them, as has been proved, extremely injurious to crops. Thus for a few days in the year at any rate these pugnacious 15 226 A HISTORY OF BIRDS and mischievous birds make some atonement for the injury they do the farmer and the gardener, to say nothing of the bird- lover, during the rest of the year. But in a very little while a vegetable diet of regurgitated seeds take the place of insect food ; and in this particular the Sparrow follows the traditions of his tribe — the Finches. The offspring of the Cormorants are fed after a fashion which savours a little of nastiness, inasmuch as the young bird thrusts its head down the parent's throat and helps himself to as much as he can swallow of his parent's last meal ! Similarly, the young Pelican helps himself to fish from his mother's pouch. To assist him she presses the pouch against her breast and raises the upper jaw. According to the legend indeed she feeds her young on her own blood ! This curious and touching conceit probably arose from the fact that a certain amount of blood from the captured fish escapes at this time. This fashion of feeding practised by the Cormorant and its near relative the Pelican is the more curious because no other members of the group to which these birds belong, except perhaps the Gannet, appear to adopt the practice. And this brings us to the sub- ject of feeding by regurgitation, which is practised by numbers of birds of quite different orders, so that it must suffice here to quote a few instances thereof. The Petrels appear always — though exceptions will probably be found — to feed their young on oil, which is distilled from the fish on which they live, in large quantities, and this is injected into the mouths of their offspring. This oil is also used, by the way, as a weapon of offence both by old and young, being squirted out from the mouth and nostrils whenever they are alarmed. Unappetising as such a diet may seem, it would nevertheless appear to be wonderfully sustaining, and no more striking proof of this could be found than that furnished by the Albatross. In the species known to science as Dioniedea extilans, at any rate, if in no other species, the nestling is at first assiduously fed until it becomes a mass of fat, even exceeding the adult in weight ! It is then deserted by its parents, who roam the winter over the ocean, leaving their down-clad and helpless offspring to the tender mercies of Fate for the space of about four months ! At last they return to the nest to find the young CARE OF OFFSPRING 227 hopeful standing, fully fledged but helpless on its edge. But this reunion is but of brief duration, inasmuch as the youngster is straightway driven off and a new nest is commenced. Never- theless, he seems loth to leave the parental dwelling, remaining in the vicinity for some months longer, but from time to time taking short trips to sea, probably accompanied by one of the parents, who plays the part of instructor. Parrots feed their offspring on regurgitated food, and also be it noted, feed one another during the process of courtship, a fact which may throw some light on the origin of this method of feeding the young. The White Stork — and probably other species — feeds its young after this fashion also, placing its beak within that of the nestling during the operation. The members of the Finch tribe, as we have just remarked, feed their young at first on insects, but later on regurgitated seeds. For the preparation of this pabulum green seeds are chosen. The Night- jar feeds by regurgitation, and so also does the House- martin, though the remaining members of the Swallow tribe feed their young on insects. This fact is interesting, showing, as it does, how careful one must be in forming conclusions as to the feeding habits of nearly allied birds based on the ob- servations of a single species. Similarly again, the Green Wood- pecker {Gecinus viridis) regurgitates, while the Greater and Lesser Spotted species retain ^ the more primitive method of rearing their young on the undigested insects. This regurgi- tated food, it should be remarked, differs among different birds in this respect, that whereas in the majority of cases it is injected into the mouth of the chick but little if at all changed, in others it is considerably changed, as in the Petrels and the Green Woodpecker. In the Pigeons again, at least during the earlier period of feeding, the regurgitated food takes the form of a milky secretion — known as " Pigeons' milk " — formed by the disintegration of the mucous membrane of the crop. The method of conveying this food also varies. Thus in the Penguin and Cormorant, for example, the young thrusts its head down the throat of the parent ; in like manner the young- Pigeon thrusts its beak within that of the parent, but it would appear that in the case of the Martin the operation is reversed. On this point, however, as in much else that concerns the feeding of the young, more observations are sadly needed. 228 A HISTORY OF BIRDS Where the young are fed on insects, either in the form of grubs or imagos, it is amazing to see the number of victims which the parents will contrive, in some mysterious way, to gather up and hold within their beaks before flying off to the nursery. The Starling and the Wagtail may be taken as examples of this custom. The Puffin, which feeds its young on fish, has acquired a marvellous skill in holding several fish in the bill at once. One can understand easily enough how one or two can be held, but how a dozen or so victims can be gathered up without the earlier ones being dropped is a mystery. Among Passerine birds both sexes share the work of feeding, and though the female is generally most assiduous, the male occasionally exceeds his mate in zeal. Mr. Farren describes the case of a pair of Chaffinches in which the male bore the brunt of the work. He generally brought food (insects) entirely concealed in his mouth. This was then regurgitated, and dis- tributed to the young according to their needs, or according to their clamour. If any inability, or disinclination, to swal