172 NATURAL HISTORY OF SELBORNE. 
spect to them, and different from all other birds, I might perhaps 
be credited ; especially as my assertion is the result of many 
years' exact observation. The fact that I would advance is, that 
swifts tread, or copulate, on the wing : and I would wish any 
nice observer, that is startled at this supposition, to use his own 
eyes, and I think he will soon be convinced. In another class 
of animals, viz. the insect, nothing is so common as to see the 
different species of many genera in conjunction as they fly. The 
swift is almost continually on the wing ; and as it never settles 
on the ground, on trees, or roofs, would seldom find opportunity 
for amorous rites, was it not enabled to indulge them in the air. 
If any person would watch these birds of a fine morning in May, 
as they are sailing round at a great height from the ground, he 
would see, every now and then, one drop on the back of another, 
and both of them sink down together for many fathoms with a 
loud piercing shriek. This I take to be the juncture when the 
business of generation is carrying on. 
As the swift eats, drinks, collects materials for its nest, and, 
as it seems, propagates on the wing ; it appears to live more in 
the air than any other bird, and to perform all functions there 
save those of sleeping and incubation. 
This hirundo differs widely from its congeners in laying in- 
variably but two eggs at a time,* which are milk-white, long, 
and peaked at the small end ; whereas the other species lay at 
each brood from four to six. It is a most alert bird, rising very 
early, and retiring to roost very late ; and is on the wing in the 
height of summer at least sixteen hours. In the longest days it 
does not withdraw to rest till a quarter before nine in the even- 
ing, being the latest of all day birds. Just before they retire 
whole groups of them assemble high in the air, and squeak, and 
shoot about with wonderful rapidity. But this bird is never so 
much alive as in sultry thundry weather, when it expresses great 
alacrity, and calls forth all its powers. In hot mornings several, 
getting together in little parties, dash round the steeples and 
churches, squeaking as they go in a very clamorous manner : 
these, by nice observers, are supposed to be males serenading 
their sitting hens ; and not without reason, since they seldom 
* This is a mistake ; three and even four eggs are not uncommon. But, if their first produce 
be taken -dway, I believe that two eggs are the maximum which are laid afterwards. Of seven 
nests, all of them containing eggs, which were removed by a correspondent of Loudon's Maga- 
zine, two of them contained only a pair, four had three, and one had as many as four eggs m 
it. On examining the same situation five weeks afterwards, eight new nests had been constructed, 
each of them containing only a pair of either eggs or young. — Ed. 
