THE VERTEBRATES: BIRDS 227 



numerous birds the young of the year, old enough to fly and 

 as large as the adults, still differ considerably in plumage 

 from the latter; males differ from females, and, finally, both 

 males and females may change their plumage (hence color and 

 markings) with the season. The seasonal changes of plum- 

 age accomplished by moulting may be marked or hardly 

 noticeable. "All birds get new suits at least once a year, 

 changing in the fall. Some change in the spring also, either 

 partially or wholly, while others have as many as three 

 changes — perhaps, to a slight extent, a few more. . . . 

 It is claimed by some that now all new colors are acquired by 

 moult, and by others that in some instances (young hawks) 

 an infusion or loss, as the case may be, of pigment takes 

 place as the feather forms, and continues so long as it grows." 

 There is much lack and uncertainty of knowledge con- 

 cerning the moulting and change of plumage by birds, and 

 careful observations by bird-students should be made on 

 the subject. 



The uses of colors and patterns in animals are discussed in Chapter 

 XXXIII. For accounts of the plumage and color of birds see Chapter 

 III in Chapman's "Bird-Life," and Chapters VIII and IX in Baskett's 

 "Story of the Birds." 



Structure and habit. — In connection with learning the 

 different kinds of birds in a locality, observations should be 

 made, and notes of them recorded, on their habits, and on 

 their external structure and its relation to the habits of the 

 bird. The interesting adaptation of structure to special 

 use is particularly well shown in the varying character of 

 the bill and feet of birds. The various feeding habits and 

 uses of the feet of different birds are readily observed. The 

 characters of bills and feet are much used in the classifica- 

 tion of birds, so that any knowledge of them gained primarily 

 in the study of adaptations will have a secondary use in 

 classification work. 



