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Show 1874.] MOLOTHRI OF BUENOS AYRES. 163 undergoes, and in the peculiar language and gestures of these four species that is complex enough ; but the complexity will probably be much increased when we become familiar with the instincts of the other members of the genus. W e may wait to hear something out of the common in their nesting-habits, as confidently as we expect to find pale green eggs in the nest of a Coccyzus or feathers in the stomach of a Grebe. April 15,1873.-This morning I started in quest of the Bay-wings. As soon as I got near them (for they were in the usual place) I observed one bird, that had somehow escaped detection the day before, assuming the purple plumage. This bird I shot; and after the flock had resettled a short distance off, I crept close up to them under the shelter of a hedge to observe them more narrowly. One of the adults was closely attended by three young birds ; and they all, whilst 1 observed them, fluttered their wings and clamoured for food each time the parent bird stirred on her perch. One of the three young birds was spotted with purple; and this bird I brought down, together with its foster-parent and one of its foster-brothers. These last two specimens (for I could see no more) were more interesting than the others I had obtained, as they had fewer purple feathers ; and it may be seen in them how closely at first these birds resemble their foster-brothers the young of M. badius. The hunger-cry of the young M. badius is quite different from that of the young M. bonariensis. The cry of the latter is a shrill two-syllabled note, the last syllable being lengthened out into a continuous squeal when the foster-parent approaches to feed it. The hunger-cry of the young M. badius is short, somewhat strident, tremulous, and unin-flected. The resemblance of the young M. rufoaxillaris to its foster-brothers in language and plumage is the more remarkable when we reflect that the adult M. rufoaxillaris in all its habits, gestures, and notes, as well as in its purple plumage, comes vastly nearer to M. bonariensis than to M. badius. It seems impossible for mimicry to go further than this. A slight difference in size is quite imperceptable when the birds are flying about; but in language and plumage the keenest ornithologist would not detect a difference. But it may be questioned whether this is in reality a case of an external resemblance of one species to another acquired by natural selection for its better preservation. Is it not as reasonable to believe that the young of M. rufoaxillaris in the first stage of its plumage exhibits the ancestral type (that of the progenitor of both species), that it has not supplanted the unvarying and consequently unimproved descendants (M. badius), simply because its elective parasitical instinct has made its existence dependent on that species 1 Did the M. badius belong to some other group, Sturnella or Pseudo-leistes for instance, it would not then be possible to doubt that the resemblance of the young M. rufoaxillaris to its foster-brothers resulted from mimicry; but as the two species belong to the limited group Molothrus the resemblance might be ascribed to community of descent. VIII. Probably Molothrus badius always hatches its own eggs. |