314 NATURAL HISTORY 



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 No- 

 vember. 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 southerly parts of 

 Andalusia, where they can be no ways in- 

 fluenced 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 moult- 

 ing, or by a disposition to rest after so rapid 

 a life, or by what ? This is one of those 

 incidents in natural history that not only 

 baffles our searches, but almost eludes our 

 guesses ! 



