FROM my boyhood, when I first began to observe birds, I started with the imbibed notion that those which paired for life were the rare exceptions--the dove that rhymed with love, the eagle, and perhaps half a dozen more. Who, for instance, would imagine that the sexes could be faithful in parasitical species like the cuckoo of Europe and the cow-birds of America? Yet even as a boy I made the discovery that an Argentine cow-bird that lays its eggs in the nests of other species, does actually pair for life; and so effectually mated is it, that on no day and no season of the year will you see a male without his female: if he flies she flies with him and feeds and drinks with him, and when he perches she perches at his side, and he never utters a sound but a responsive sound immediately falls from her devoted beak.
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Again, it may seem unlikely that there can be pairing for life in species, like the chaffinch of northern Europe and, with us, of Scotland, in which the sexes separate and migrate separately. Also of non-gregarious species like the nightingale in which the males arrive in this country several days before the females. Yet I am confident that if we could catch and mark a considerable number of pairs it would be found that the same male and female found one another and re-mated every year.
It comes to this, that birds may pair for life, yet not be all the time or all the year together, as in the case of hawks, crows, owls, herons, and many others. In numberless species which undoubtedly pair for life the sexes keep apart during several hours each day, and there is some evidence that those that separate for a part of the year remain faithful.
An incident, related by Miss Ethel Williams, of Winchester, in her natural history notes contributed to a journal in that city, bears on this point. She had among the bird pensioners in the garden of her house adjoining the Cathedral green, a female thrush that grew tame enough to
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fly into the house and feed on the dining-room table. Her thrush paired and bred for several seasons in the garden, and the young, too, were tame and would follow their mother into the house to be fed. The male was wild and too shy ever to venture in. She noticed the first year that it had a wing-feather which stuck out, owing probably to a malformation of the socket. Each year after the breeding season the male vanished, the female remaining alone through the winter months, but in spring the male came back--the same bird with the unmistakable projecting wing-feather. Yet it was certain that this bird had gone quite away, otherwise he would have returned to the garden, where there was food in abundance during the spells of frosty weather. As he did not appear it is probable that he migrated each autumn to some warmer climate beyond the sea.