CHAPTER II 



EXTERNAL FEATURES BIOLOGICALLY CONSIDERED 



§ 1. Shape and Pose. § 2. The Skin. § 3. Plumage of Birds. 

 § 4. Moulting of Feathers. § 5. Coloration. 



§ I. Shape and Pose 



It may be said that there are two main shapes among birds — 

 (a) the Running Bird type, with considerable erectness, 

 familiar in ostriches and also in some young birds like 

 chicks, and (b) the Flying Bird type, where the body is 

 more boat-like and the whole attitude less erect. When a 

 Flying Bird or Carinate is adapted more to terrestrial than 

 to aerial locomotion, the shape and pose have a superficial 

 approximation to the Running Bird type> as is very well 

 seen in a bird like the Bittern which has a somewhat flagging 

 flight and often stands very erect like an overgrown chick. 

 When, on the other hand, the Flying Bird is much given to 

 swimming or to swimming and diving, the bulk of the body 

 is very boat-like, the neck often rising at right angles. 

 When a bird markedly adapted to aquatic life has its legs 

 very far back, its pose on land may be very erect, and as the 

 instep of the foot may then be flush with the ground instead 

 of at right angles to it, as in most birds, the creature looks 

 almost as if it were sitting on its tail. The instep may be 

 on the ground ; yet in the familiar case of the puffin, which 

 looks as if it were resting on its tail, the bird is almost 

 always standing on its toes in the orthodox way. 



It is evident that the peculiarities of the plumage con- 

 tribute not a little to what is characteristic in a bird's external 

 appearance. A tern is marked by its long narrow wings 

 and its forked tail, but this individuality is gone when the 



