As a matter of fact, there is no need for any such elaborate deception. Up to the moment of hatching, the little foster-parents have in all probability no suspicion of the trick that has been played on them. Birds do not take deliberate notice of the size or colour of their own eggs. Kearton somewhere relates how he once induced a blackbird to sit on the eggs of a thrush, and a lapwing on those of a redshank. So, too, farmyard hens will hatch the eggs of ducks or game birds and wild birds can even be persuaded to sit on eggs made of painted wood. Why then, since they are so careless of appearances, should the cuckoo go to all manner of trouble to match the eggs of hedgesparrow, robin or warbler? The bird would not notice the difference, and, even if she did, she would probably sit quite as close, if only for the sake of the other eggs of her own laying. Once the ugly nestling is hatched, there comes swift awakening. Yet there is no thought of reprisal or desertion. It looks rather as if the little foster-parents are hypnotised by the uncouth guest, for they see their own young ones elbowed out of the home and continue, with unflagging devotion, to minister to the insatiable appetite of the greedy little murderer. A bird so imbued as the parasitic cuckoo with the _Wanderlust_ would make a very careless parent, and we must therefore perhaps revise our unflattering estimate of its attitude and admit that it does the best it can by its offspring in putting them out to nurse. This habit, unique among British birds, is practised by many others elsewhere, and in particular by the American troupials, or cattle-starlings. One of these indeed goes even farther, since it entrusts its eggs to the care of a nest-building cousin. There are also American cuckoos that build their own nest and incubate their own eggs. On the whole, our cuckoo is a friend to the farmer, for it destroys vast quantities of hairy caterpillars that no other bird, resident or migratory, would touch. On the other hand, no doubt, the numbers of other small useful birds must suffer, not alone because the cuckoo sucks their eggs, but also because, as has been shown, the rearing of every young cuckoo means the destruction of the legitimate occupants of the nest. So far however as the farmer is concerned, this is probably balanced by the reflection that a single young cuckoo is so rapacious as to need all the insect food available.