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Show 1874.] MOLOTHRI OF BUENOS AYRES. 155 habits of the bird, gives its own egg the best chance of being preserved ; for though the Molothrus never distinguishes its own eggs, of which indeed it destroys many, those with soft shells have the poorest chance of being preserved whenever several in the nest are indiscriminately broken. 2. The vitality or tenacity of life appears greater in the embryo M. bonariensis than in other species; this circumstance also, in its relation to the egg-breaking habit and to the habit of laying many eggs in a nest, gives it a further advantage. I have examined nests of the Scissor-tail containing a large number of eggs, after incubation had began, and have been surprised at finding all the eggs of the Scissor-tail addled, even when they were placed most advantageously in the nest for receiving the heat of the sitting bird ; whilst those of the M. bonariensis contained living embryos, even when under all the other eggs, and, as frequently happens, glued immovably to the nest by the matter of broken eggs spilt over them before incubation had commenced. 3. The comparatively short time the embryo takes to hatch gives it another and a great advantage ; for, whereas the eggs of other small birds require to be sat on from fourteen to sixteen days, that of M. bonariensis hatches in eleven days and a half from the moment incubation commences; so that when the female M. bonariensis makes so great a mistake as to lay an egg with others that have already been sat on, if incubation is not far advanced, her egg has still a chance of being hatched before or contemporaneously with the others ; but even if the others hatch before it, the extreme hardiness of the embryo serves to keep it alive with the modicum of heat which it still receives from the foster-bird. 4. Whenever the M. bonariensis is hatched together with the young of its foster-parents, if these are smaller than the parasite (and in most cases they are smaller), soon after exclusion from the shell they disappear, and the young M. bonariensis remains sole occupant of the nest. How the latter succeeds in expelling or destroying them, if he indeed does destroy them, I have not been able to learn. To all these circumstances favourable to the M. bonariensis may be added another of equal or greater importance. The M. bonariensis never being engaged with the dilatory and exhaustive process of rearing its own young, and for this reason continuing in better condition than other birds, and moreover being gregarious and practising promiscuous sexual intercourse, must lay a vastly greater number of eggs than other species. In our domestic fowls we see that hens that never become broody frequently lay many dozens of eggs more in a season than others. Some of our small birds rear two, others but one brood in a season-building, incubation, and tending the young taking up much time, so that they are usually from two to three months and a half employed. But the M. bonariensis is like the fowl that never incubates, and continues dropping eggs over four months and a half. From the beginning of September till the end of January the males are seen incessantly wooing the females; and during most of this time the eggs are found. I find that small birds will, if de- |
