NATURAL HISTORY OF SELBORNE. 



133 



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 mo're 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 occa- 

 sionally 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 1 This is one of those incidents in 

 natural history that not only baffles our searches, but almost eludes our 

 guesses ! 



These hirundines never perch on trees or roofs, and so never con- 

 gregate 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. 



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. 



They never can settle on the ground but through accident ; and when 

 down, can hardly rise, on account of the shortness of their legs and 

 the length of their 

 wings; neither can 

 they walk, but only 

 crawl; but they 

 have a strong 

 grasp with their 

 feet, by which 

 they cling to walls. 

 Their bodies being 

 flat they can enter 

 a very narrow 

 crevice ; and where 

 they cannot pass 

 on their bellies 

 they will turn up 

 edgewise. 



The particular formation of the foot discriminates the swift from all 

 the British hirundines ; and indeed from all other* known birds, the 



WHITE-BELLIED SWIFT. 



