BRITISH BIRDS. 309 



with bolder wing than the Swallows, with which 

 they never intermingle. The life of the Swift 

 seems to be divided into two extremes; the one 

 of the most violent exertion, the other of perfect 

 inaction; they must either shoot through the air, 

 or remain close in their holes. They are seldom 

 seen to alight; but if by any accident they should 

 fall upon a piece of even ground, it is with diffi- 

 culty they can recover themselves, owing to the 

 shortness of their feet, and the great length of 

 their wings. They are said to avoid heat, and 

 for this reason pass the middle of the day in their 

 holes; in the morning and evening they go out in 

 quest of provision ; they then are seen in flocks, 

 describing an endless series of circles upon circles, 

 sometimes in close ranks pursuing the direction of 

 a street, and sometimes whirling round a large 

 edifice, all screaming together; they often glide 

 along without stirring their wings, and on a sud- 

 den they move them with frequent and quickly 

 repeated strokes. Swifts build generally in lofty 

 steeples and high towers : sometimes under the 

 arches of bridges, which, though their elevation 

 is not great, are difficult of access : the nest is 

 composed of a variety of materials, such as dry 

 grass, moss, hemp, bits of cord, threads of silk and 

 linen, small shreds of gauze, of muslin, feathers, 

 and other light substances which they chance to 

 find in the sweepings of towns. It is difficult to 

 conceive how these birds, which are never seen 

 to alight, gather such materials; some have sup- 

 posed that they catch them in the air as they are 

 carried up by the wind ; others, that they raise 

 them by glancing along the surface of the ground : 



