CLASSIFICATION 



139 



Figure 140. — Different Kinds of 

 Birds' Feet. 



134. Plumage. — The 



feathers of birds show 



great variety in form and 



color. In some species 



there are certain colors 



which always predomi- 

 nate on the males, while 



the females have little 



color ; in other species 



it is hard to distinguish 



between the sexes. The 



brilliantly colored males 



are supposed to attract 



the females at the mating season, while the dull colored 



females are inconspicuous and less likely to be attacked 



by enemies while hatching their eggs, or caring for their 



young. We may say, 

 therefore, that they are 

 protectively colored. 

 The color of birds varies 

 during the first two or 

 three years of life. 



135. Classification. — 

 Birds are usually di- 

 vided into groups ac- 

 cording to their struc- 

 ture. The shape and 

 size of the beak and of 

 the feet and wings are 

 the characteristics most 

 used in the general 

 classification. This is 

 illustrated by a single 

 Figure 141. — Loggerhead Shrike. group of birds, the 



