OF SELBORNE. 17.", 



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*. 



Sw r ifts 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. 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 myste- 

 rious 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 southerly parts of An- 

 dnlutiia, where they can be no ways influenced by any defect 

 of heat ; or, as one might suppose, defect of food. Are they 

 regulated in their motions with us by a failure of food, or by a 

 propensity to moulting, or by a disposition to rest after so 



* [Mr. Yarrell has the following observation on this question in Mr. 

 Bennett's edition, p. 277 : " The swift departs before its moult, and when 

 its plumage is at the worst from wear and tear. Our summer visitors 

 generally complete their moult before they leave us, but not the Ifirun- 



Dr. Jenner's observations indisputably prove that swifts return year 

 after year to the >ame breeding-place. One of them, which he had marked 

 by the amputation of two of its toes, was seen to revisit its old haunts 

 seven years after. T. B.] 



