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 
