Origin of Species Variorum

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 any 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 .. size .. and the period of 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. Mr. Ramsay remarks that two of the Australian cuckoos, when they lay their eggs in an open ... nest, manifest a decided preference for nests containing eggs similar in colour to their own. The European species certainly manifests some tendency towards a similar instinct, but not rarely departs from it, as is shown by her laying her dull and pale-coloured eggs in the nest of the Hedge-warbler with .. bright greenish-blue eggs. Had our cuckoo invariably displayed the above instinct, it would assuredly have been added to those which it is assumed must all have been acquired together. The eggs of the Australian Bronze cuckoo vary, according to Mr. Ramsay, to an extraordinary degree in colour; so that in this respect, as well as in size, natural selection assuredly might have secured and fixed any advantageous variation. ↑

With reference to the ... young European cuckoo ejecting its foster-brothers— must first be remarked that Mr. Gould, who has paid particular attention to this subject, is convinced that the belief is an error; he asserts that the young foster-birds are generally ejected during the first three days, when the young cuckoo is quite powerless; he maintains that