332 INSTINCTS OF THE CUCKOO. [Chap. VTH. 



observations, 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 voracious 

 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 adaptation 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 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 

 l'.ronze cuckoo the eggs vary greatly in size, from eight 

 to ten lines in length. Xow 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. Eamsay 

 remarks that two of the Australian cuckoos, when they 



