424 A HISTORY OF BIRDS 



tails ; Humming-birds suspend themselves in mid-air before 

 the flowers while they extract therefrom honey and insects : 

 but the dull and heavy Toucan is obliged to adopt the tactics 

 just described. 



The insectivorous birds display no less variety in the shape 

 of the bill. In many of the small perching birds, such as the 

 Robin and Wagtail, it is small, and differs but little in shape 

 from that of many seed-eaters. In others, as in the Tree-creepers, 

 it is long, slender and decurved. The former picks up insects 

 when at rest, the latter has to hunt for them amid the crevices 

 of the bark of trees. In the Jacamars it is long and pointed, 

 as in the fish-eating Kingfishers, In the Flycatcher it is short, 

 broad and greatly depressed : these birds catch their prey as 

 it flies. In the Swallows, Swifts and Night-jars, the beak is 

 reduced to its smallest possible dimensions and the gape deeply 

 cleft so that in the Night-jar the angle of the mouth extends 

 backwards to terminate below the eyes ; and these all capture 

 small insects in mid-air, rushing along at great speed. In the 

 case of these swift-winged birds there can be no doubt but that 

 the peculiar form of the bill is a direct adaptation to the capture 

 of insect food. Not so, however, is the case of the large number 

 of Kingfishers which live entirely on insect prey far from water. 

 The beaks of these birds are as certainly special adaptations for 

 the capture of small fish. But it is easy here to see how the 

 changed diet came about, inasmuch as even the most con- 

 firmed fish-eaters eat largely of the small Crustacea and aquatic 

 insect lavae which abound in streams. From prey of the latter 

 kind it is but a step to an exclusively insect diet which can be 

 obtained independently of the presence of streams. That this 

 is so we may gather from the fact that these insectivorous types 

 capture their victims exactly as their relatives capture fish — by 

 darting suddenly upon them from a sallying point to which 

 they return. 



The enormous mouths of the aberrant Night-jars known as 

 "Frog-mouths" would appear to have been acquired before 

 they lapsed into the sluggish habits of to-day. They feed, like 

 Night-jars, on insects, but these are captured not while the bird 

 is on the wing, but by hunting among the branches of the trees. 

 These birds appear to vary their diet with fruit and small 

 mammals. This last fact is important as indicating the incipient 



