THE KOEL 121 



thus managed to have their offspring reared for them, 

 while those that attempted to build fresh nests dropped 

 their eggs before the new nurseries were ready, natural 

 selection would tend to weed out the latter and thus 

 the parasitic habit might arise, until eventually the koel 

 came to forget how to build a nest. 



In this connection it is important to bear in mind 

 that the nearest relatives of the koel are non-parasitic. 

 It is therefore not improbable that in the koel the para- 

 sitic habit has an independent origin. 



This instinct has undoubtedly been evolved more 

 than once. It does not necessarily follow that similar 

 causes have led to its origin in each case. 



The suggestion I have made is made only with 

 reference to the koel, which differs from other cuckoos 

 in that it dupes a bird stronger and bigger than itself. 

 But this is a digression. 



If the koel have time, she destroys one or more of the 

 existing eggs, and will sometimes return later and 

 destroy others. Although the crow cannot distinguish 

 between her own and koel's eggs, the koel can. I have 

 come across several crows' nests which each contained 

 only two koel's eggs. 



The young koel is a better-behaved bird than some 

 of its relations, for it ejects neither the eggs still in the 

 nest when it is hatched nor its foster-brethren. But 

 the incubating period of the koel is shorter than that of 

 the crow, so that the koel's egg is always the first to 

 hatch out. The koel seems never to make the mistake 

 of depositing its egg among nearly incubated ones. 

 Thus the young koel commences life with a useful start 



