618 COLLEGE ZOOLOGY 



erratic course without difficulty. The tail is light, and therefore 

 easy to manage, and the tail-feathers (rectrices, Fig. 471, RX) 

 are firmly supported by the terminal bone of fused vertebrae, 

 the pygostyle (Fig. 471, Q). Movement of the tail is allowed 

 by the freely movable vertebras just preceding the pygostyle. 

 While perching the tail acts as a " balancer." Birds that cling 

 to the sides of trees, like the woodpeckers (Fig. 503), or to the 

 sides of other objects, like the chimney-swift, brace themselves 

 by means of their tails. 



In many birds the tail of the male differs from that of the 

 female, being more beautiful in the former, and serving as a 

 sexual character. Two of the most famous of these dimorphic 

 species are the lyre-bird (Fig. 505, A) and the birds of paradise 

 (Fig. 505, B). 



Feet. - - The feet (Fig. 506) are used for locomotion, for ob- 

 taining food, for building nests, and for offensive and defensive 

 purposes. Ground-birds usually have strong feet, fitted for 

 running (Fig. 506, A), or scratching (c); perching birds (see p. 

 6 1 6) possess feet adapted for grasping a perch (d) ; aerial birds 

 use their feet very little, and these organs are consequently weak 

 (a, e) ; swimming birds (/', /, n) and wading birds (g, k, m) are 

 provided with toes that are more or less completely lobed ; birds 

 of prey possess strong feet with sharp claws (/) for capturing 

 other animals; woodpeckers have feet (b) adapted for clinging 

 to the bark of trees. 



Bills. - - The bills of birds (Fig. 507) serve as hands, and their 

 most important function is to procure food. Since bills are also 

 used to construct nests, to preen feathers, and to perform other 

 duties, their adaptations are such as to make them serve several 

 purposes. In preening the feathers a drop of oil is pressed from 

 the oil-gland at the base of the tail and spread by means of the 

 bill. 



Seed-eating birds possess short, strong bills for crushing seeds 

 (Fig. 507, c); birds that eat insects have longer and weaker bills 

 (d, q); birds of prey are provided with strong, curved beaks 



