Amongst ducks, the male has no care for his progeny. The male eider resembles the duck in this respect (Audubon). Male turkeys do much worse: they often devour the eggs of their females, and thus oblige the latter to hide them.[46] Female turkeys join each other with their young ones for greater security, and thus form troops of from sixty to eighty individuals, led by the mothers, and carefully avoiding the old males, who rush on the young ones and kill them by violent blows on the head with their beaks.[47] Among certain species of gallinaceæ the male leaves to the female the care of incubation and of rearing the young. During this time he is running after adventures, but returns when the young are old enough to follow him and form a docile band under his government.[48] It is important to notice that, amongst birds, the fathers devoid of affection generally belong to the less intelligent species, and are most often polygamous. It seems, therefore, that polygamy is not very favourable to the development of paternal love.[49] But bad fathers are rare amongst birds. Often, on the contrary, the male rivals the female in love for the young; he guards and feeds her during incubation, and sometimes even sits on the eggs with her. The carrier pigeon feeds his female while she is sitting;[50] the Canadian goose[51] and the crow do the same; more than that, the latter takes his companion’s place at times, to give her some relaxation. The blue marten behaves in the same manner.[52] Among many species, male and female combine their efforts without distinction of sex; they sit in turn, and the one who is free takes the duty of feeding the one who is occupied. This is the custom of the black-coated gull,[53] the booby of Bassan,[54] the great blue heron,[55] and of the black vulture.[56] According to Audubon, the blue bird of America works so ardently at the propagation of its species that a single brood does not satisfy him; each couple, therefore, exerts itself zealously, rearing two or three broods at the same time, the female sitting on one, while the male feeds the little ones of the preceding brood.[57]