Some birds are content with very little care for home-building ready for their eggs. Birds belonging to many different species make nurseries in hollow trees, caves, burrows or natural cavities, sometimes lining them with leaves and feathers to make them soft, but sometimes even neglecting this care. The New Zealand kakapo or ground parrot, to take one instance, hides in any hole it finds and lays its eggs there without any preparation; the kingfisher, again, digs out a hole in the ground, or occupies one that it finds. Emus scrape a shallow hole in the ground and do not cover the eggs. The cassowary scrapes together a rude pile of leaves and mould on which she lays the eggs. Some of the megapodes or bush turkeys bury their eggs in the sand, and then take no further trouble about them, leaving incubation to the chance warmth of the sun. Others build enormous heaps of decaying leaves, forming a hot-bed from natural fermentation, by which the chicks are hatched out with no trouble to the parents. The young of the megapodes are the only living birds that are hatched out able to fly at once and ready to take care of themselves. It would appear that neglectful parents foster self-development in the children.[43] Where the mother broods alone over the eggs it sometimes happens that the father-bird takes no interest in the family. The polygamous gallinaceous birds appear to be without, or to have lost, the paternal instinct. Peacocks, pheasants, turkey-cocks, and barn-door cocks do practically nothing for their families, and while the mother-birds’ care in feeding and guarding the young is untiring, the fathers are running after amorous adventures. The conduct of the male turkey is even worse, for, prompted by jealousy, he will often attempt to devour the eggs, and the young are protected from his attacks only by the mothers uniting together in troops. Here we see the exact opposite conduct in the two sexes from that in such a family as the sticklebacks, where good fathers replace bad mothers. But the same result follows. In either case the neglect of parental duty by one or other parent is a source of weakness to the family and increases the risks to which the young are exposed.[44] I must insist on how strongly conduct is affected by the conditions of the home; and any change of habits will directly modify parental behaviour. Thus an animal habitually domestic may easily change under the pressure of external causes. Thus wild ducks, though good parents and strictly monogamous, and very highly developed in social qualities when in the wild state, become indifferent to their offspring and loosely polygamous under domestication.[45] Civilisation, in this case, depraves the birds as often it does men. But the examples of bad parents among birds are few in number.