XXVIII 



BEAKS 



THE beaks of birds are formed on the same lines 

 as the horns of antelopes (see p. 266). There is a 

 core, formed by prolongations of those bones known 

 as the upper and the lower jaw, covered with a 

 modification of skin known as horn ; this outer 

 covering, or sheath, is as insensitive as the horn- 

 sheath of a buffalo, goat, sheep,, or antelope. The 

 base of the sheath (known as the cere) softens where 

 it becomes continuous with the feather-covered skin 

 on the bird's head. 



The beaks of birds are used for offensive and defensive 

 purposes : also for constructing nests, .but above all 

 things for obtaining food, and for this purpose it is 

 often strangely modified. Long thin beaks are useful 

 for obtaining worms from soft mud ; and long, strong 

 and sharp beaks are used by herons and darters to 

 secure slippery creatures like fish. Beaks which are 

 short, but strong and sharp, enable many birds to 

 extract the kernels of nuts, or grubs from the trunks 

 and branches of trees. By means of powerful, sharp, 

 and hooked beaks, birds of prey are able to rend the 

 carcases of animals ; ducks, by means of flat, spatulate 

 bills, sift mud and ooze to obtain the organisms 

 necessary for their sustenance ; with their stout beaks 

 open-bills can break the shells of molluscs and extract 

 the soft animal within. 



