T'he Natural History of Selborne 255 



some time before their congeners 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 

 tenth of August, and sometimes a few days sooner ; and every 

 straggler invariably withdraws by the zoth, while their con- 

 geners, 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 southerly parts of Andalusia, where 

 they can be in no ways influenced by any defect of heat, or, 

 as one might suppose, failure of food. Are they regulated in 

 their motions with us by a defect 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 searches, buf almost eludes our 

 guesses. 1 



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 in- 

 fested with those pests to the genus called hippoboscce hirun- 

 dinis, and often wriggle and scratch themselves in their flight 

 to get rid of that clinging annoyance. 



Swifts are no songsters, and have only one harsh screaming 

 note ; yet there are ears to which it is not displeasing, from 

 an agreeable association of ideas, since that note never occurs 

 but in the most lovely summer weather. 



1 It, is really the question of food-supply that regulates their move- 

 ments. ED. 



