They often lay so many eggs--from fifteen
to twenty--in the same foster-nest, that few or none can possibly be
hatched. They have, moreover, the extraordinary habit of pecking holes in
the eggs, whether of their own species or of their foster parents, which
they find in the appropriated nests. They drop also many eggs on the bare
ground, which are thus wasted. A third species, the M. pecoris of North
America, has acquired instincts as perfect as those of the cuckoo, for it
never lays more than one egg in a foster-nest, so that the young bird is
securely reared. Mr. 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?"
Various birds, as has already been remarked, occasionally lay their eggs in
the nests of other birds. This habit is not very uncommon with the
Gallinaceae, and throws some light on the singular instinct of the ostrich.
In this family several hen birds unite and lay first a few eggs in one nest
and then in another; and these are hatched by the males. This instinct may
probably be accounted for by the fact of the hens laying a large number of
eggs, but, as with the cuckoo, at intervals of two or three days.
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