THE BIOLOGY OF BIRDS 



CHAPTER I 



THE CHIEF CHARACTERISTICS OF BIRDS 



§ I. Intensity of Life in Birds. § 2. Running and Parachuting before 

 Flying. § 3. Supply of Body with Arterial Blood Exclusively. 

 § 4. Warm-bloodedness. § 5. Feathers. § 6. Adaptations Acces- 

 sory to Flight. § 7. Mentality of Birds. § 8. Nesting. 

 § 9. Migration. 



To say that birds are feathered bipeds Is certainly to define 

 them off from all other animals, but it leaves much to be 

 said. Even when we add two other words and make the 

 compact definition " warm-blooded, oviparous, feathered 

 bipeds," there is not more than a suggestion of the singularly 

 attractive reality. It is impossible to get the picturesque 

 impression, which is at least part of the truth, without 

 more details. Let us attempt an introductory statement 

 of the salient characteristics of birds. 



§ I. Intensity of Life in Birds 



Instead of beginning with feathers and flight, it may be 

 possible to get further back and recognise the bird as a 

 creature of intense metabolism. This, we think, is the 

 heart of the matter, that whereas reptiles are on the whole 

 slow-going, the bird that arose millions of years ago from 

 one of the reptilian stocks diverged in the direction of 

 living much more nearly up to its income. Its constitution 

 was geared to a higher rate than that of reptiles. This 

 seems to have been an ever recurrent dichotomy in evolu- 

 tion, a separation of the slow-goers from the quick-goers, 



B 



