THE VERTEBRATES: BIRDS 



233 



tion with the observation of the differences in flight habit. 



The tongues and tails of birds are two other structures 

 the modifications and special uses of which may be readily 

 observed and studied. Note the structure and special use 



FIG. 125. Gulls soaring. (Photograph by O. H. von Bargen, on San 

 Francisco Bay; permission of Camera Craft.} 



of the tongue and tail (fig. 123) of the woodpeckers; note 

 the tongue of the humming-bird; the tail of the grackles. 



Feeding habits, economics, and protection of birds. 

 The feeding habits of birds are not only interesting, but 

 their determination decides the economic relation of birds 

 to man, that is, whether a particular bird species is harmful 



