148 THE NATURAL HISTORY 



continually feeding them every two or three minutes ; while swifts, 

 that have but two young to maintain, are much at their leisure, 

 and do not attend on their nests for hours together. 



Sometimes they pursue and strike at hawks that come in their 

 way ; but not with that vehemence and fury that swallows express 

 on the same occasion. They are out all day long in wet days, 

 feeding about, and disregarding still rain : from whence two things 

 may be gathered ; first, that many insects abide high in the air, 

 even in rain ; and next, that the feathers of these birds must be 

 well preened to resist so much wet. Windy, and particularly windy 

 weather with heavy showers, they dislike ; and on such days with- 

 draw, and are scarce ever seen. 



There is a circumstance respecting the colour of swifts, which 

 seems not to be unworthy our attention. When they arrive in 

 the spring they are all over of a glossy, dark soot-colour, except 

 their chins, which are white ; but, by being all day long in the sun 

 and air, they become quite weather-beaten and bleached before 

 they depart, and yet they return glossy again in the spring. Now, 

 if they pursue the sun into lower latitudes, as some suppose, in 

 order to enjoy a perpetual summer, why do they not return 

 bleached ? Do they not rather perhaps retire to rest for a season, 

 and at that juncture moult and change their feathers, since all 

 other birds are known to moult soon after the season of breeding ? l 



Swifts are very anomalous in many particulars, dissenting from 

 all their congeners not only in the number of their young, but in 

 breeding but once in a summer ; whereas all the other British 

 hirundines breed invariably twice. It is past all doubt that swifts 

 can breed but once, since they withdraw in a short time after the 

 flight of their young, and some time before their congeners bring 

 out their second brood. We may here remark, that, as swifts 

 breed but once in a summer, and only two at a time, and the 

 other hirundines twice, the latter, who lay from four to six eggs, 

 increase at an average five times as fast as the former. 



But in nothing are swifts more singular than in their early 

 retreat. They retire, as to the main body of them, by the tenth 

 of August, and sometimes a few days sooner : and every straggler 

 invariably withdraws by the twentieth, while their congeners, all 

 of them, stay till the beginning of October ; many of them all 



1 [The swift, like the swallow, moults after it leaves us. The ' ' bleaching " of the 

 feathers here alluded to, is not so much the result of the sun's heat, as of the wear 

 and tear of constant rapid flight. The edges of the feathers become worn, and lose 

 their glossy appearance.] 



