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COLLEGE ZOOLOGY 



Seed eating 

 (sparrow) 



Insecf eating 

 (nighthawk) 



Tearing 

 (hawk) 



Probing 

 (woodcock) 



Capturing fish 

 (merganser) 



Figure 316. Some types of feet and bills of birds and their adaptations. 



Bills 



The bills of birds (Fig. 316) serve as 

 hands, and their most important function is 

 to procure food. Since bills are also used to 

 construct nests, to preen feathers, and to 

 perform other duties, their adaptations are 

 such as to make them serve several purposes. 

 In preening the feathers, a drop of oil is 

 pressed from the oil gland at the base of 

 the tail and appears to be spread on the 

 feathers by means of the bill. At least in 

 the waterfowl, the oil serves as a "dressing" 

 that keeps the feathers in good condition. 

 Another function of the oil is to prevent 

 the covering of the bill from becoming 

 brittle. There is also evidence that the oil 

 gland has an antirachitic function. Experi- 

 mental removal of the gland in some birds 

 causes rickets. 



Seed-eating birds possess strong short bills 

 for crushing seeds (Fig. 316); some birds 

 that eat insects have smaller and weaker 

 bills; birds of prey are provided with strong 

 curved beaks fitted for tearing flesh; and 

 some birds have serrated bills for holding 

 fish. Many other examples might be cited. 



which show the evolutionary possibilities of 

 a simple organ. 



Colors of birds 



Birds are among the most beautifully 

 colored of all animals. Some colors are due 

 to pigments within the feather; these in- 

 clude pigment granules of brown, black, or 

 dull yellow, and carotenoids either red or 

 yellow. Green, blue, and iridescent markings 

 as on some hummingbirds are due to the 

 peculiar surface structure of their feathers. 

 Absence of pigment causes partial or com- 

 plete albinos. The juvenal plumage of birds 

 gives way to the first winter plumage; this 

 is usually worn throughout the first winter 

 and is generally dull in color, often resem- 

 bling the plumage of the adult female. 

 Males and females frequently differ in color 

 (sexual dimorphism), especially during the 

 breeding season, when the male may acquire 

 a brightly colored coat; the cardinal and 

 scarlet tanager exhibit marked sexual dimor- 

 phism. 



Color is often of protective value to the 



