160 THE WORLD'S BIRDS. 



grade, not standing upon the toes. They climb 

 and cling well, but only a few perch on trees in the 

 ordinary way. They are seldom seen otherwise 

 than on the wing. 



FLIGHT. Swift and easy, some being said to be the 

 swiftest of all birds. Sometimes they cannot rise 

 off the ground, but not by any means always. 



NOTE. A twitter or scream. They never sing as some 

 swallows do. 



DISPOSITION AND HABITS. Lively and sociable ; they 

 are also courageous, often turning sparrows and 

 swallows out of their nests. 



ECONOMIC QUALITIES. Except when they displace 

 swallows, they are highly beneficial by reason 

 of their feeding habits. One species (Collocalia 

 francica), which builds entirely with its sticky 

 saliva, produces the valuable " edible birds' - 

 nests " of Eastern commerce. 



CAPTIVITY. They have never been kept in this state 

 for any length of time. 



DISTRIBUTION AND IMPORTANT SPECIES. There are 

 about a hundred species in this family, which 

 is found all round the world, chiefly in warm, 

 but also in temperate climates ; those frequenting 

 the latter migrate south in winter ; there are none 

 in New Zealand. The familiar sooty-brown British 

 species (Cypselus apus) extends over a large part 

 of the Old World ; but the common Swift of tropical 

 Africa and India is Cypselus affinis, smaller and 

 blacker than the British species, with a white 

 patch on the back. The Great Alpine Swift 

 (Cypselus melba), light brown above, white below, 

 is also a widely-distributed European species, but 

 only a straggler in England. The common Swift 

 of North America is the Chimney Swift (Chaetura 

 pelasgia), black, with a spiny tail, building a nest 

 of glued twigs in chimneys. 



