THE WORLD'S BIRDS. 83 



INCUBATION. About a fortnight. 



FOOD. Insects, generally captured on the wing. 



GAIT. A walk or hop ; but they seldom move much 

 on foot. When perching, they sit along the bough, 

 not across it. 



FLIGHT. Very light and easy ; most of their active 

 life is spent on the wing. 



NOTE. Remarkable and characteristic, and varying 

 much according to the species ; often like articulate 

 sounds. 



DISPOSITION AND HABITS. The birds being generally 

 nocturnal, these are not much known. They are 

 usually solitary, and keep quiet by day. Some 

 have a habit of making a noise by clapping their 

 wings together in flight. 



ECONOMIC QUALITIES. Nightjars are some of the most 

 useful of birds as insect-destroyers, and do no 

 harm whatsoever. 



CAPTIVITY. They are difficult to keep, as they generally 

 refuse to feed themselves ; but our species (Capri- 

 mulgus eiiropaeus] has been maintained for some 

 time. 



DISTRIBUTION AND IMPORTANT SPECIES. Nightjars, 

 of which there are about a hundred and twenty 

 species, are found all round the world, chiefly in the 

 tropics ; those of temperate climates are migra- 

 tory. Their notes afford the most striking distinc- 

 tion ; the purring sound produced by the European 

 species is well known, also the " chook-chook," 

 resembling a stone sent skimming over ice, of the 

 common Indian species (Caprimulgus asiaticus), 

 and the curious calls of the American Whip-poor - 

 Will (C. vociferus) and Chuck- Will's -widow (C. 

 carolinensis). The Night-hawk (C. popelue), also 

 American, is to a great extent a diurnal species. 



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