178 NATURAL HISTORY OF SELBORNE. 
them every two or three minutes; while swifts, that have but two 
young to maintain, are much at their leisure, and do not attend on 
their nests for hours together. 
Sometimes they pursue and strike at hawks that come in their 
way; but not with that vehemence and fury that swallows express 
on the same occasion. They are out all day long in wet days, feed- 
ing about, and disregarding still rain : from whence two things may 
be gathered ; first, that many insects abide high in the air, even in 
rain ; and next, that the feathers of these birds must be well preened 
to resist so much wet. Windy, and particularly windy weather, 
with heavy showers, they dislike ; and on such days withdraw, and 
are scarce ever seen. 
There is a circumstance respecting the colour of swifts, which 
seems not to be unworthy of our attention. When they arrive in 
the spring, they are all over of a glossy, dark soot colour, except 
their chins, which are white ; but, by being all day long in the sun 
and air, they become quite weather-beaten and bleached before 
they depart, and yet they return glossy again in the spring. Now, 
if they pursue the sun into lower latitudes, as some suppose, in order 
to enjoy a perpetual summer, why do they not,return bleached ? 
Do they not rather perhaps 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 asummer; 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 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 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 beginning of November. This early 
retreat is mysterious and wonderful, since that time is often the 
sweetest season inthe year. But what is more extraordinary, they 
