OF SELBORNE. 313 



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 re- 

 turn 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 par- 

 ticulars, 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 inva- 

 riably 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 conge- 

 ners bring out their second broods. We 

 may here remark, that as swifts breed but 

 once in a Summer, and only tieo 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. 



