228 The Bird 



beaks that a new trick is learned in a very short time. 

 In captivity a crow, when it thinks no one is watching, 

 will often take a morsel of food, thrust it beneath a piece 

 of sod, and cover it up with grass, almost with one 

 motion of the beak. 



Functional or adaptive radiation is beautifully il- 

 lustrated by the beak of a gannet, cormorant, snake- 

 bird, and pelican birds which are closely related to 

 one another structurally, also having in common a fish 

 diet, swallowing their prey whole. The gannet's beak 

 is thick and very strong, and along the inner edge is a 

 series of fine serrations pointing backward. The bird 

 dives, from a great height, into the water and seizes the 

 fish in a grip of steel. The upper mandible of the cor- 

 morant is furnished with a large, sharp hook, with which 

 the bird gaffs its prey, pursuing it under water. The 

 snake-bird, or darter, has a bill like a needle, with which 

 it spears the fish, impaling it through and through; while 

 the pelican, because of its great pouch least vicious of 

 all in its methods, simply engulfs the fish, the water in 

 which it is swimming and all, then straining out the liquid, 

 tosses the unfortunate into the air and swallows it 

 head first. The under mandibles of this bird are long 

 and pliable and so arranged that they can bend far apart, 

 thus making of the great bag of skin beneath the bill 

 and throat an admirable fish-trap. 



This is one of the many instances where several closely 

 related species, with needs so similar that there is danger 

 of fatal competition, are able to exist in great numbers 

 and to avoid all undue struggle for existence by having 



