The Cuckoo arrives in this country about the middle of April; the time of its coming to different countries is adapted to the time of the foster-parents' breeding. During the whole of its stay it leads a wandering life, building no nest, and attaching itself to no particular locality. It shows no hostility towards birds of another kind, and little affection for those of its own. If two males meet in the course of their wandering they frequently fight with intense animosity. I was once witness of an encounter between two birds who chanced to meet in mid-air. Without alighting they attacked each other with fury, pecking at each other and changing places just as one sees two barn-door cocks fight for the supremacy of the dunghill. Feathers flew in profusion, and in their passion the angry birds heeded my presence so little that they came almost within arm's length of me. These single combats account for the belief formerly entertained that the Cuckoo was the only sort of Hawk that preyed on its own kind. The female does not pair or keep to one mate. It is, however, frequently accompanied by a small bird of another kind, said to be a Meadow Pipit.
The Cuckoo hunts for its food both in trees and on the ground. On its first arrival it lives principally on beetles, but when caterpillars become abundant it prefers them, especially the hairy sorts. In the months of May and June, the female Cuckoo lays her eggs (the number of which is variously estimated from five to twelve), choosing a separate locality for each, and that invariably the nest of some other bird. The nests in which the egg of a Cuckoo has been found in this country are those of the Hedge Sparrow, Robin, Redstart, Whitethroat, Willow Warbler, Sedge Warbler, Wagtail, Pipit, Skylark, Yellow Bunting, Chaffinch, Greenfinch, Linnet, Blackbird and Wren; the Pipit being the most frequent. It has now been ascertained that the nests of birds in which the Cuckoo lays its eggs in different countries number 145 species.[24] In some of these instances, the position and structure of the nests were such that a bird of so large a size could not possibly have laid an egg in the usual way. Hence, and from other evidence, it is pretty clear that the egg is in all cases laid at a distance from the nest and carried by the bird in her bill to its destination. The bird can have no difficulty in accomplishing this seemingly hard task; for the gape of the Cuckoo is wide, and the egg disproportionately small, no larger in fact than the egg of the Skylark, a bird only a fourth of its size. The period during which a nest is fit for the reception of a Cuckoo's egg is short; if a time were chosen between the completion of the nest and the laying of the first egg by the rightful owner, the Cuckoo could have no security that her egg would receive incubation in good time, and again if the hen were sitting there would be no possibility of introducing her egg surreptitiously. She accordingly searches for a nest in which one egg or more is laid, and in the absence of the owner lays down her burden and departs. There are certain grave suspicions that the intruder sometimes makes room for her own egg by destroying those already laid; but this, if it be true, is exceptional. If it were very much larger than the rest, it might excite suspicion, and be either turned out, or be the cause of the nest being deserted; it would require, moreover, a longer incubation than the rest, and would either fail to be hatched, or produce a young Cuckoo at a time when his foster-brothers had grown strong enough to thwart his evil designs. As it is, after fourteen days' incubation, the eggs are hatched simultaneously, or nearly so, the Cuckoo being generally the first. No sooner does the young bird see the day, than he proceeds to secure for himself the whole space of the nest and the sole attention of his foster-parents, by insinuating himself under the other young birds and any eggs which may remain unhatched, and hurling them over the edge of the nest, where they are left to perish. 'The singularity of its shape', says Dr. Jenner, 'is well adapted for these purposes; for, different from other newly-hatched birds, its back from the shoulders downwards is very broad, with a considerable depression in the middle. To the question which naturally suggests itself, 'Why does the young Cuckoo thus monopolize the nest and the attentions of its foster parents?' the solution is plain. The newly-hatched bird must of necessity be less in size than the egg from which it proceeded, but a full-grown Cuckoo exceeds the dimensions of a whole brood of Pipits; its growth therefore must be rapid and cannot be maintained without a large supply of food.