332 INSTINCTS OF THE CUCKOO. [Chap. VIIl 



oLservations, we have learnt 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 vora- 

 cious young bird receives ample food. 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 adapta- 

 tion we may infer from the fact of the non-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 ar- 

 rangement, 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 advan- 

 tage 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. Mr. Eam- 

 say remarks that two of the Australian cuckoos, when 



