1 88 NATURAL HISTORY OF SELBORNE. 



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 diffei s widely from its congeners in laying invariably 

 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 evening, 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 thundery 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 squeak till they come 

 close to the walls or eaves, and since those within utter at the same 

 time a little inward note of complacency. 



