228 THE WORLD OF ANIMAL LIFE 



are also fond of small spiders, which they pick out from the centre 

 of their webs. And some humming-birds will poise themselves in 

 front of a leaf or twig, and pick off, one after another, the tiny 

 insects that are feeding upon it. 



In order to enable these birds to extract both insects and nectar 

 from flowers, their tongues are very curiously made. Instead of 

 being short, thick, and fleshy, like those of very many birds, they 

 are very long, and so slender as to be almost hair-like, and are double 

 in structure, so that they can be passed far down into the interior 

 of the flower, and can lick out every insect and every particle of 

 nectar that it contains. 



As is the case with many birds whose powers of flight are 

 greatly developed, the legs of humming-birds are small and weak. 

 In this respect these birds resemble our own swallows and swifts, 

 which can dash to and fro all day long upon untiring wing, but 

 cannot walk, or even stand, upon the ground without difficulty. 

 But a humming-bird seldom perches except at night, and then 

 not upon the ground, so that its marvellous powers of flight more 

 than compensate for the weakness of its limbs. 



These birds are called "humming"-birds because of the hum- 

 ming or buzzing sound which is made by the rapid vibration of 

 their wings as they hover in front of a flower. We may hear a 

 similar sound when watching one of the humming-bird hawk-moths, 

 of which we have already spoken. 



Travellers tell us that different kinds of these birds produce 

 different sounds, and that it is often possible to detect the species 

 to which a humming-bird belongs by simply listening to the buzz- 

 ing of its wings. One bird is said to produce a sound just like that 

 of a blue-bottle fly, while the hum of another is compared to the 

 whizzing of a wheel driven by machinery. 



THE NIGHTJAR (Family Caprimulgid^) 



On a warm summer evening, when the air is still, you may hear 

 a very strange and curious sound. It is not at all easy to describe, 

 but is something like the whirring of a wheel in rapid motion, or 



