Page:The Zoologist, 4th series, vol 5 (1901).djvu/490

460 necessarily, have been the desire to shelter and conceal the eggs. It is possible that both that and the idea of doing so were developed after, and by reason of the nest itself, which, in its early stages, may have been due to other and widely different causes. Eggs and young must, of necessity, be preceded by sexual intercourse, and in the case of the Crested—probably of all the Grebes—it seems likely that such intercourse takes place on the nest alone. With the vast majority of birds, however, this is quite otherwise. Pairing on the nest, if it takes place at all (I have observed it in the case of the Rook, which again brings us nearer to the Bower-birds), does so probably as an exception, nor is it easy to see why this should ever have been otherwise. But (if I may be allowed to sketch my theory first, and give the facts on which I found it afterwards) let us assume two things, neither of which, perhaps, is highly improbable—viz.: first, that the primæval bird, or birds, made no nest; and, secondly, that the first eggs were laid on the ground. Supposing, then, that a male ground-laying bird that makes no nest indulges during the season of love, till shortly before the actual laying of the eggs, in all sorts of strange frenzied movements upon the ground, and that these movements tend to become localized and concentrated in some particular spot or spots in which—or one of which—the female, as sexually attracted thereto, ultimately lays her eggs, have we not here the nucleus, or, at any rate, the potentiality, of the future nest? And where—before the eggs were laid—would pairing have been so likely to have taken place as in one of these very spots—these vortexes, so to speak, of the sexual whirlwind? Can we not imagine a custom, gradually shaping itself out of this, of laying the eggs in some place where pairing was habitually indulged in, so that if such place afterwards became, in any true sense, a nest, we would here have habitual pairing upon it?

Having got so far, let us now suppose that one chief form of these frenzied movements alluded to, is a rolling upon or a buzzing or spinning over the ground, by which means the bird so acting produces a larger or smaller depression in it. If the eggs are laid in such a depression, they are now laid in a nest, but such nest will not have been produced with any idea of concealing the eggs or sheltering the young. It will be due to nervous and non-purposive movements springing out of the violence of