Secondly, that the eggs are remarkably
small, not exceeding those of the skylark--a bird about one-fourth as large
as the cuckoo. That the small size of the egg is a real case of adaptation
we may infer from the fact of the mon-parasitic American cuckoo laying
full-sized eggs. Thirdly, that the young cuckoo, soon after birth, has the
instinct, the strength and a properly shaped back for ejecting its foster-
brothers, which then perish from cold and hunger. This has been boldly
called a beneficent arrangement, in order that the young cuckoo may get
sufficient food, and that its foster-brothers may perish before they had
acquired much feeling!
Turning now to the Australian species: though these birds generally lay
only one egg in a nest, it is not rare to find two and even three eggs in
the same nest. In the bronze cuckoo the eggs vary greatly in size, from
eight to ten lines in length. Now, if it had been of an advantage to this
species to have laid eggs even smaller than those now laid, so as to have
deceived certain foster-parents, or, as is more probable, to have been
hatched within a shorter period (for it is asserted that there is a
relation between the size of eggs and the period of their incubation), then
there is no difficulty in believing that a race or species might have been
formed which would have laid smaller and smaller eggs; for these would have
been more safely hatched and reared.
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