29 o ECONOMIC ZOOLOGY AND ENTOMOLOGY 



keys refer to adult birds, and in ordinary plumage. Among 

 numerous birds the young of the year, although 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 

 plumage accomplished by molting 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 molt, 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 concern- 

 ing the molting and change of plumage by birds, and careful 

 observations by bird students should be made on the subject. 



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 dif- 

 ferent kinds of birds in a locality, observations should be made, 

 and notes of them recorded, on their habits, and on their ex- 

 ternal structure and its relation to the habits of the bird. 

 The interesting adaptation of structure to special use is particu- 

 larly 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, and the accompanying 

 modification of bills and feet can be readily seen in birds pre- 

 served as "bird-skins." In some cases the general structure 

 of feet and bills may be seen in the live birds by the use of an 

 opera-glass. The characters of bills and feet are much used 

 in the classification of birds, so that any knowledge of them 

 gained primarily in the study of adaptations will have a 

 secondary use in classification work. 



Note the foot of a robin, bluebird, catbird, wren, warbler, or 

 other Passerine or perching bird. It has three unwebbed toes 



