182 THE NATURAL HISTORY 



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 ? 



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 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 through that month, and 

 some occasionally to the beginning of November. This 

 early retreat is mysterious and wonderful, since that time 

 is often the sweetest season in the year. But, what is more 

 extraordinary, they begin to retire still earlier in the most 



