158 



ANIMAL BIOLOGY 



like the leaves of trees, are delicate structures and lose 



perfect condition with age. Hence the annual renewal 



of the feathers is 

 an advantage. Most 

 birds shed twice a 

 year, and with many 

 the summer plum- 

 age is brighter col- 

 ored than the winter 

 plumage. When a 

 feather is shed on 

 one side, the corre- 

 sponding feather on 

 the other side is 



always shed with it. (What need for this ?) A large 



oil gland is easily found on the 



dorsal side of the tail. How does 



the bird apply the oil to the 



feathers ? 



FIG. 295. WING OF BIRD. 



/, false quills (on thumb) ; 2, primaries; 5, secondaries; 

 tertiaries (dark) are one above another at right; 

 a, b t coverts. 



A 



FIG. 296. 



A t point dividing primaries from second- 

 aries; B, coverts. 



In describing and classifying 

 birds, it is necessary to know the 

 names of the various external 

 regions of the body and plum- 

 age, These may be learned by 

 studying Figs. 295, 296, 297, 298. 



FIG. 297. CEDAR WAXWING, 

 with regions of body marked. 



S, forehead; Sc, crown (with crest); 

 Hh, nape; K, throat; Br, breast; 

 Ba, lower parts; R, back; Rt, tail; 

 B, tail coverts; P, shoulder feathers 

 (scapulars) ; T, wing coverts; HS, 

 primaries; AS, secondaries; A I, 

 thumb feathers. 



The quills on the hand 



