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But this gratitude of the Crustacean towards a sympathetic bivalve is merely a hypothesis; we do not exactly know what passes in the intimacy of these two widely-differing natures. For birds like the Cuckoo and the Molothrus it is not possible to plead attenuating circumstances. They occupy a place in an inhabited house without paying any sort of rent. Every one knows the Cuckoo's audacity.
The cowbird belongs to the family of birds scientifically known as Icteridae, which includes such familiar species as the bobolinks, orioles, meadowlarks, and the various kinds of blackbirds, none of which, I am glad to say, are parasites. The name Molothrus has been given to the genus that includes the cowbirds.
The habits of the Molothrus bovariensis, a closely allied Argentine Cow-bird, have been carefully studied by Mr. W. H. Hudson, who has also some interesting remarks as to the vestiges of the nesting instinct in this interesting parasitical bird, which now is constantly dropping eggs in all sorts of places, even on the ground, most of them being lost.
These birds show a love of independence very rare among animals, with whom conjugal fidelity has become proverbial; they do not unite in couples; unions are free, and the mother hastens to deliver herself from the cares of bringing up her young in the manner we have seen. Two other species of Molothrus have the same habit, as have the American Cuckoo and the Golden Cuckoo of South Africa.
Swainson has well remarked, that with the exception of the Molothrus pecoris, to which must be added the M. niger, the cuckoos are the only birds which can be called truly parasitical; namely, such as "fasten themselves, as it were, on another living animal, whose animal heat brings their young into life, whose food they live upon, and whose death would cause theirs during the period of infancy."
Swainson has well remarked, that with the exception of the Molothrus pecoris, to which must be added the M. niger, the cuckoos are the only birds which can be called truly parasitical; namely, such as "fasten themselves, as it were, on another living animal, whose animal heat brings their young into life, whose food they live upon, and whose death would cause theirs during the period of infancy."
The instinct, however, of the American ostrich, as in the case of the Molothrus bonariensis, has not as yet been perfected; for a surprising number of eggs lie strewed over the plains, so that in one day's hunting I picked up no less than twenty lost and wasted eggs. Many bees are parasitic, and regularly lay their eggs in the nests of other kinds of bees.
Absence of Trees. Deer. Capybara, or River Hog. Tucutuco. Molothrus, cuckoo-like habits. Tyrant-flycatcher. Mocking-bird. Carrion Hawks. Tubes formed by Lightning. House struck. In the morning we got under way, and stood out of the splendid harbour of Rio de Janeiro. In our passage to the Plata, we saw nothing particular, excepting on one day a great shoal of porpoises, many hundreds in number.
As soon as the little Molothrus feels his body covered with feathers and his little wings strong enough to sustain him he quits his adopted parents without consideration.
Hudson is a strong disbeliever in evolution, but he appears to have been so much struck by the imperfect instincts of the Molothrus bonariensis that he quotes my words, and asks, "Must we consider these habits, not as especially endowed or created instincts, but as small consequences of one general law, namely, transition?"