CHAPTER XIII 



BIRDS 



133. Birds. — Birds are the only vertebrates covered with 

 feathers. Their front legs are modified into wings. 

 Among some birds, like the penguins (pen'gwinz) of the 

 Antarctic region, the wings are not used for flying but to 

 assist in swimming. In others, like the eagles and condors, 



the expanse of the wings 

 is sufficient to enable 

 them to fly away with 

 young lambs and large 

 fish. Between the small 

 wings of the penguin 

 and the great expanse of 

 the wings of the eagle 

 and the condor there 

 are many variations. 

 Bird wings are adapted 

 to the needs of their 

 owners. Sailing birds, like the gulls, have long, slender 

 wings, while ground birds, like the partridge and pheasant, 

 have short wings capable of rapid, short flights. Those 

 birds that make the most use of wings have them best 

 developed. An example of underdevelopment, which has 

 been increased by domestication, is seen in the domestic 

 fowl, a ground bird, which makes little use of its flying 

 powers, and is incapable of sustained flight. 



The legs of birds also have many variations. In the case 



136 



Figure 136. — Grebe. 



