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Show 164 MR. W. H. HUDSON ON THE [Mi -Formerly I believed that though the M. badius is constantly observed to nidificate, they also occasionally dropped their eggs in the nests of other birds (see P. Z. S. 1870, p. 671). I could not doubt that this was the case after having seen a couple of their young following a Yellowbreast and being fed by it. But later and more careful observations, together with the discovery I have just recorded, have made me alter my opinion. What then appeared to be proof positive is now no proof at all; the young birds I observed were perhaps those of M. rufoaxillaris. Indeed it is much more probable that they should have belonged to this than to the other species, since the Bay-wings are constantly seen to rear their own young, whereas I have never found a nest of M. rufoaxillaris, and believe they are altogether parasitical. IX. Reasons for believing that the M . rufoaxillaris is parasitical almost exclusively on M . badius.-I have spoken of the many varieties of eggs M. bonariensis lays. Those of the M. badius are a trifle less in size, in form elliptical, very thickly and uniformly marked with small spots and blotches of dark reddish colour varying to dusky brown; the ground-colour is white, but sometimes, though rarely, a very pale blue. It is not possible to confound the eggs of the two species M. bonariensis and M. badius. Now, ever since I saw, many years ago, the Yellowbreast already mentioned tending the young Bay-wings, I have looked out for the eggs of the latter species in other birds' nests. I have found many hundreds of nests containing eggs of M. bonariensis, but never one with an egg of M. badius, and, I may now add, never with an egg of M. rufoaxillaris. It is wonderful that M. rufoaxillaris should lay only in the nests of M. badius ; but the most mysterious thing is • that M. bonariensis, which apparently lays in as many nests as ever it can find, never, to m y knowledge, drops an egg in the nest of M. badius! It will be hard for naturalists to believe this; for if the M. badius is so excessively vigilant and jealous of all other birds approaching its nest as to succeed in keeping out the subtle, silent, grey-plumaged, ever-present M. bonariensis, why does it not also keep off the rarer, noisy, bustling, rich-plumaged M. rufoaxillaris 1 But this bird may enter the nest forcibly. The M. badius may also possess sagacity sufficient to distinguish the eggs of M. bonariensis from its own and cast them out of the nest. This poiut must remain unsettled. X. Comparative perfection of the parasitical instinct of Molothrus rufoaxillaris.-It is with a considerable degree of repugnance that we regard the parasitical instinct in birds : the reason it excites such a sensation is manifestly because it presents itself to the mind, in the words of a naturalist who lived a hundred years ago and believed the Cuckoo had been created with such a habit, as " a monstrous outrage on the maternal affection, one of the first great dictates of nature " - an outrage, since each creature has been endowed with the all-powerful affection for the preservation of its own, and not another, species ; and here we see it by a subtile process, an unconscious iniquity, turned from its original purpose, perverted, and made subservient to .•• |