NATURAL HISTORY OF SELBORNE 151 



haps 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 ? 



Swifts 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 broods. We may here re- 

 mark, 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 roth 

 August, and sometimes a few days sooner ; and every strag- 

 gler invariably withdraws by the 2Oth, while their congeners, 

 all of them, stay till the beginning of October ; many of them 

 all through that month, and some occasionally to the begin- 

 ning of November. This early retreat is mysterious and won- 

 derful, 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, 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. 



Swifts are no songsters, and have only one harsh screaming 



