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the central facts of its life is seen in many of its relations to its offspring.
Birds undoubtedly have a strong emotional concern over their eggs and
young, but it is an instinctive, irrational concern, not an instinct
entwined, as is the human parents' concern, with reason, memory,
personal affection, and foresight. A pair of birds is robbed of their
whole brood; the parental instinct fmds itself frustrated, and they
will show great agitation. But if one or more of the nestlings die
before they are fledged—a frequent and in some species a normal
occurrence—the old birds show no signs of sorrow or even agitation,
but merely throw the corpse out of the nest as if it were a stick or a
piece of dirt. And while a chick is, to our eyes, obviously failing, the
old birds, far from making special efforts to restore it, as would human
parents, definitely neglect it. The fact seems to be that the bird
parent feels parental only when stimulated by some activity on the
part of its children. When they gape and squawk, this is a stimulus to
the parent to feed and tend them assiduously; when the stimulus
fails, the parental feeling is no longer aroused, the bird is no longer
impelled to parental actions.
This same incapacity to experience things as men and women
would experience them is shown by the fact that if you remove young
birds from a nest, as Mr. Kearton did with some starlings, and sub-
stitute some eggs, the mother, after a moment's apparent surprise,
may accept the situation with equanimity, and respond to the new
stimulus in the proper way, by silling on the eggs. There was no trace
of the distraction and grief which a human mother would have felt.
But perhaps the familiar cuckoo provides us with the completest
proof, over the widest field, of the dissimilarity of birds' minds with
our own. The young cuckoo, having been deposited as an egg in the
nest of some quite other species of bird—a meadow-pipit, say, or a
hedge-sparrow—and having hatched out in double-quick time, the
rate of its embryonic development being adjusted to its parasitic
habits, so that it shall not lag behind its foster-brothers, next proceeds
to evict all the rest of the contents of the nest, be these eggs or young
birds. It is provided with a flat and indeed slightly hollow back;
and, hoisting its victim on this, it crawls backwards up the side of the
nest, to pitch the object outside. Thus it continues to do until the
nest is empty^.
What cruelty, you will say, and what unpleasant ingenuity! But
you will be wrong. The nestling cuckoo is not cruel, nor does he know
why he is murdering his fellow nest-mates. He acts blindly, because
he is a machine constructed to act thus and not otherwise. Not only
is his back slightly concave, but this concavity is highly irritable and