OCR Text |
Show 172 MR. W. H. HUDSON O N T H E [Mar. 3, little space, she will return again and again, as if fascinated with the comfort and security of such an abode. It is amusing to see how pertinaciously they hang about the ovens of the Oven-bird3, apparently determined to take possession of them, flying back to them after a hundred repulses, and yet not entering them, even when they have the opportunity. Sometimes one is seen following a Wren or a Swallow to its nest beneath the eaves, and then clinging to the wall beneath the hole into which it disappeared. I could fill many pages with instances of this habit of the M. bonariensis, which, useless though it be, is as strong an affection as the bird possesses. That it is a recurrence to a long disused habit, I can scarcely doubt; at least, to no other cause, that I can imagine, can it be attributed ; and, besides, it seems to m e that if the M. bonariensis, when once a nest-builder, had acquired the semiparasi-tical habit of breeding in domed nests of other birds, such a habit might conduce to the formation of the instinct which it now possesses. Iu m y former letter on the M. bonariensis I mentioned that twice I had seen birds of this species attempting to build nests, and that on both occasions they failed to complete the work. So universalis the nest-making instinct that one might safely say the M. bonariensis had once possessed it, and that in the cases I have mentioned it was a recurrence, too weak to be efficient, to the ancestral habit. Another interesting circumstance may be adduced as strong presumptive evidence that the M. bonariensis once made itself an open exposed nest as M. badius occasionally does-viz. the difference in colour of the male and female ; for whilst the former is rich purple, the latter has what naturalists consider an adaptive resemblance in colour to the nest and to the shaded ulterior twigs and branches on which nests are usually built. How could such an instinct have been lost ? To say that the M. bonariensis occasionally dropped an egg in another bird's nest, and that the young hatched from these accidental eggs possessed some (hypothetical) advantage over those hatched in the usual way, and that so the parasitical habit became hereditary, supplanting the original one, is an assertion without any thing to support it, and seems to exclude the agency of external conditions. Again the want of correspondence in the habits of the young parasite and its foster-parents would in reality be a disadvantage to the former; the unfitness would be as great in the eggs and other circumstances. For all the advantages the parasite actually possesses in the comparative hardness of the egg-shell, rapid evolution of the young, &c, already mentioned, must have been acquired little by little through the slowly accumulating process of natural selection, but subsequently to the formation of the original parasitical inclination and habit. I am inclined to believe that M. bonariensis lost the nest-making instinct by acquiring that semiparasitical habit, common to so many South-American birds, of breeding in the large covered nests of the Dendrocolaptidse. We have evidence that this semiparasitical habit does tend to eradicate the nest-making one. The Synallaxes build great elaborate domed nests ; yet we have one species (S. agithaloides) that never builds for itself, but breeds in the |