178 NATURAL HISTORY OF SELBORNE. 



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 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 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 November. This early 

 retreat is mysterious and wonderful, since that time is often 

 the sweetest season in the year. But what is more extra- 

 ordinary, 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 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 hippo- 

 boscce 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 



