190 NATURAL HISTORY OF SELBORNE. 



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

 and do not attend on their nest 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 withdraw, and are scarce ever seen. 



There is a circumstance respecting the colour of swifts, which 

 seems not to be unworthy of 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? 



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 hirun- 

 dines 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 broods. 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 loth August, and 

 sometimes a few days sooner; and every straggler invariably 

 withdraws by the 2oth, while their congeners, all of them, stay till 

 the beginning of October ; many of them all through that month, 



