NATURAL HISTORY OF SELBORNE 79 



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 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 ? x 



Swifts are very anomalous in many particulars, dissent- 

 ing 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 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 tenth of August, and sometimes a few days sooner : 



1 Although the fact is not generally known, even at this day, there can be no 

 doubt that Gilbert White was perfectly right in his surmise that Swifts moult after 

 they leave this country. Mr. Hartert, our greatest authority on the order of 

 Swifts, tells me that he has examined moulting specimens of the common Swift 

 killed in the winter home of the species. [R. B. S.] 



