viii CONTENTS 



CHAPTER TACK 



VIII. Migration i6o 



Main Facts regarding Migration, i6o. Problems in Process of 

 Solution, 163. Nature of the Migratory Custom, 167. Imme- 

 diate Stimuli liberating the Migratory Impulse, 168. The 

 Problem of Way-Finding, 170. Possible Origin of the Migratory 

 Custom, 174. 



IX. Courtship and Sex 176 



Physiological and Psychological, 176. Modes of Courtship 

 summarised, 177. The Mating Behaviour of Pigeons, 177. 

 The Courtship of the Great Crested Grebe, 180. The Observa- 

 tions of Selous, 184. The Evolution of the Voice, 190. Ihc 

 Variety of Bird Song, 191. The Vocal Organs, 193. The Inter- 

 pretation of Song, 195. Reconsideration of Darwin's Theory of 

 Sexual Selection, 198. Sex-Characters, 206. Hormones and 

 Sex-Characters, 228. What Determines Sex? 233. 



X. Birds' Eggs 243 



The Making of the Egg, 243. Yolk-forming, 248. Maturation 

 of the Ovum, 253. The Male Reproductive System, 254. 

 Fertilisation, 256. The Further History of the Fertilised Ovum, 

 258. Early Development, 262. Hatching, 269. The Natural 

 History of Birds' Eggs, 271. Possible Uses of Egg-Coloration, 

 278. Fertility and Fecundity, 281. Sterility, 284. 



XI. Parental Care and Nest-making 287 



Incubation, 288. Nest-making, 294. Feeding the Young, 302. 

 Educating the Young, 305. Defence of the Young, 308. The 

 Case of the Cuckoo, 309. The Case of the Mound-Birds, 311. 

 Social Life, 314. Retrospect on the Evolution of Parental 

 Care, 316. 



XII. Senses, Instincts, and Intelligence .... 318 

 The Eye, 319. The Ear, 328. The other Sense-Organs, 330. 

 The Inclined Plane of Animal Behaviour, 332. Instinctive Be- 

 haviour, 338. Intelligent Behaviour, 341. 



XITI. The Pedigree of Birds 345 



The Oldest Known Bird, 345. Affiliation of Birds to Reptiles, 

 347. Resemblances in the Development of Birds and Reptiles, 

 349. From which Reptilian Stock? 350. Speculations, 352. 

 Primitive Toothed Birds, 354. Running Birds, 356. Flying 

 Birds, 360. The Process of Evolution, 360. 



XIV. Birds and Evolution 363 



The Fact of Evolution, 363. Factors in Evolution, 365. Origi- 

 native Factors, 366. Illustrations of Variations, 371. Possible 

 Origins of Variations, 373. Modifications in Birds, 376. Modi- 

 ficational Specific Characters, 382. Directive Factors : Processes 

 of Selection, 383. Isolation and the Reverse : In-breeding and 

 Out-breeding, 386. Birds and Heredity, 387. 



XV. Birds and the Web of Life 39S 



Nutritive Inter-relations, 398. Waves of Life, 402. Repro- 

 ductive Inter-relations, 403. Parasites of Birds, 405. Strange 

 Linkages, 406. The Hand of Man on Birds, 408. The Inter- 

 Linking of Lives, 414. The Conservation of Birds, 415. 



BIBLIOGRAPHY : L A few General Books on Birds. 

 II. Books and Papers referred to in the Text . 419 



INDEX 430 



