Adaptation in Parasitic Cuckoos^ ^99^' 393 



In Hyderabad, liowever, we find quite the most wonderful 

 case of adaptation occurring amongst the eggs of parasitic 

 Cuckoos. In this town in the Deccan and the surrounding 

 country, the most common little Warbler appears to be 

 Frinia social is, belonging to that section of the genus 

 which lays a brilliant brick-red egg. The Plaintive Cuckoo 

 (C. jyasserinus), having decided that this bird is, locally, the 

 best fosterer, accordingly puts its egg into the Warbler's 

 nest, but elimination has here gone on until it has evolved a 

 red egg, quite near enough in colour to deceive the foster- 

 parent. 



A series of these eggs is especially interesting as showing 

 fairly clearly how adaptation of the Cuckoos' eggs is arrived 

 at, for although the extremes of the types are startling in 

 their contrast, eggs are obtained which show intermediate 

 stages of development. 



Judging from a series such as this, it would appear that 

 amongst the many individiials upon which these Cuckoos 

 foist their domestic duties there are a considerable number 

 which do detect the differences betweeu their own eggs and the 

 Cuckoos' eggs. When the differences are very conspicuous, 

 some of the eggs get left unattended to, and the strain 

 which lays them dies out, whilst those which lay the less 

 conspicuous eggs increase in numbers. Thus from generation 

 to generation the process of elimination goes on until a 

 state of perfection is arrived at, which suffices to invariably 

 deceive the bird it is intended to cuckold. In this instance 

 we have the Plaintive Cuckoo, which normally lays a very 

 different egg, here in the Deccan gradually reduced to a 

 strain of birds which lay red eggs not very unlike those of 

 the locally most popular form of foster-mother. 



Hierococcyx nisicolor. — If we are to judge by the degree 

 of perfection arrived at in the adaptation of their eggs to 

 those of their fosterers, then the genus Hierococcyx must be 

 held to be the oldest form of Cuckoo, with the exception 

 of the genus Coccystes, for the eggs of all three of our 

 Indian forms — H. nisicolor, H. varius, and H. sparveroides — 

 have undergone a process of elimination long enough to 



2e3 



