The Audubon Societies 



103 



alike, adapted to spearing fish, but in other respects they are very different and 

 no one would think of calling them closely related. 



A good example of divergent evolution, on the other hand, occurs among 

 the Gulls, Terns, and Skimmers, which are really closely related as shown 

 by their anatomical structure, forming the order Longipennes, but which have 

 bills which are extremely different in form, probably because of their differ- 

 ent feeding habits. Shrikes, Grosbeaks, and Warblers, of the order Passeres, 

 likewise, are similar in all their structures except their bills, and it is natural 

 to suppose that they had a common ancestor and that their variously shaped 

 bills have arisen as adaptations to particular feeding habits. But, as before 

 intimated, it may be that the history of these birds was the other way around, 



BLACK TERN KINGFISHER GREEN HERON 



Similar feeding habits have produced similar bills in these birds, which are but distantly related 



and that these diverse bills have persisted from the thousands of possible varia- 

 tions of their ancestors because the individuals were able to adapt their habits 

 to fit their modified structures. Indeed there is much evidence to support the 

 belief that both factors have been important in the course of evolution. 



Irrespective of how the changes have come about, let us consider some 

 of the structures or implements of birds in relation to the birds' methods of life. 

 Let us suggest in a few paragraphs a field that promises rich rewards to the 

 careful observer. — A. A. A. 



THE IMPLEMENTS OF BIRDS 



With Photograph by the Author 



When one passes through the halls of any of our large museums and in- 

 spects the collections of mounted birds from all over the world, one is impressed 

 by the great variety of form and color. Almost every imaginable combination of 

 colors is found represented in the plumage of some bird, and the many modifica- 

 tions of size and shape are such as to leave one confused by the heterogeneous 

 assemblage. One is almost led to believe that Nature has given loose rein to her 

 imagination and allowed her most fantastic dreams to take the form of birds. 

 Yet we are constrained to believe that there is a reason for everything, that 

 no structure exists unless perfectly adapted to the function which it has to 



