278 NATURAL HISTORY 



of their young, but in breeding but once in a summer; 

 whereas all the other British Hirundines breed invari- 

 ably 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 con- 

 geners 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 10th of August, and sometimes a few days 

 sooner: and every straggler invariably withdraws by 

 the 20th, 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 wonder- 

 ful, 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 Anda- 

 lusia, 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 rapid a life, or by 

 what? This is one of those incidents in natural history 

 that not only baffles our researches, but almost eludes 

 our guesses ! 



These Hirundines never perch on trees or roofs, and 

 so never congregate with their congeners. They are 

 fearless while haunting their nesting places, and are 

 not to be scared with a gun ; and are often beaten down 

 with poles and cudgels as they stoop to go under the 

 eaves. Swifts are much infested with those pests to 

 the genus called Hippoboscce Hirundinis ; and often 

 wriggle and scratch themselves, in their flight, to get 

 rid of that clinging annoyance. 



