CLASS AVES. BIRDS 



445 



Figure 314. King penguin. These antarctic birds are unable to fly. Their forehmbs are paddle- 

 hke flippers which are used like oars. When on land penguins usually assume an upright posture. 

 They do not build a nest, but have a special brood pocket between their legs for keeping an 

 egg warm. (Courtesy of N.Y. Zoological Society.) 



preceding the pygostyle. While perching, 

 the tail acts as a balancer. Birds that cling 

 to the sides of trees, like the woodpeckers 

 (Fig. 322), or to the sides of other objects, 

 like the chimney swift, brace themselves by 

 means of their stiff tails. 



In many birds the tail of the male differs 

 from that of the female; it is more beautiful 

 in the former and serves as a secondary sex- 

 ual character. Among the most famous of 

 these dimorphic forms of birds are the lyre 

 bird, peacock, and turkey. 



Feet 



Feet (Fig. 316) are used for locomotion, 

 for obtaining food, for building nests, and 

 for offensive and defensive purposes. Many 

 ground birds have strong feet fitted for 

 scratching; perching birds possess feet 

 adapted for grasping a perch; most swim- 

 ming birds have webbed feet; wading birds 

 have long legs and long toes; and birds of 

 prey such as the hawk possess very strong 

 feet with long sharp claws for capturing 

 other animals. 



Figure 315. Hoatzin of South America, unique 

 in many ways. The young bird, as shown here, has 

 claws on its wings and climbs about among the 

 branches. It is regarded as a survivor of that ancient 

 period when birds were distinctly reptilian in char- 

 acter. (Photo by Beebe.) 



terminal bone of fused vertebrae, the pygo- 

 style (Fig. 309). Movement of the tail is 

 allowed by the freely movable vertebrae just 



