And analogy would lead us to believe that the
young thus reared would be apt to follow by inheritance the occasional and
aberrant habit of their mother, and in their turn would be apt to lay their
eggs in other birds' nests, and thus be more successful in rearing their
young. By a continued process of this nature, I believe that the strange
instinct of our cuckoo has been generated. It has, also recently been
ascertained on sufficient evidence, by Adolf Muller, that the cuckoo
occasionally lays her eggs on the bare ground, sits on them and feeds her
young. This rare event is probably a case of reversion to the long-lost,
aboriginal instinct of nidification.
It has been objected that I have not noticed other related instincts and
adaptations of structure in the cuckoo, which are spoken of as necessarily
co-ordinated. But in all cases, speculation on an instinct known to us
only in a single species, is useless, for we have hitherto had no facts to
guide us. Until recently the instincts of the European and of the non-
parasitic American cuckoo alone were known; now, owing to Mr. Ramsay's
observations, we have learned something about three Australian species,
which lay their eggs in other birds' nests. The chief points to be
referred to are three: first, that the common cuckoo, with rare
exceptions, lays only one egg in a nest, so that the large and voracious
young bird receives ample food.
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