254 The Natural History of Se I borne 



whence we may conclude that birds whose way of life keeps 

 them perpetually on the wing would not be able to quit their 

 nest till the end of the month. Swallows and martins, that 

 have numerous families, are 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 swal- 

 lows 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 hirundines breed invariably twice. 1 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 



i See note on p. 251. ED. 



