SWIFTS. 207 



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 with- 

 draws 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 

 extraordinary, they begin to retire still earlier in the 

 more southerly parts of Andalusia, where they can 

 be nowise influenced by any defect of heat, or, as 

 one might suppose, defect of food. Are they regu- 

 lated 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 hippoboscte 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. 



