174 NATURAL. HISTORY OF SELBORNE. 
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 m 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, 
feeding 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 parti- 
cularly windy weather with heavy showers, they dislike ; and on 
such days withdraw, and are scarce ever seen. 
Tliere is a circumstance respecting the colour of s^dfts, which 
seems not to be umvorthy 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 bleachea 
before they depart, and yet they return glossy again in the sprmg. 
Now, if they pursue the sun into lower latitudes, as some suppose, 
in order to enjoy a perpetual summer, why do they not returr 
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 a summer ; whereas all the other 
British hirmidines 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. W^e 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 strag- 
* Swifts invariably moult during their absence ; and 1 am greatly inclined to suspect that the 
young undergo no change whatever until the second autumn, as is the case with the whole falcon- 
family, certain of the owls, and the bee-eater and king-fisher tribes, all of which re(iuiro a Icng 
time lo elaborate their first or nestling plumage, and many of which (I believe all the faleon- 
race) do not propagate till they are two years old. — Ed. 
