The Evolutionary History 



of the 

 Avian Genus Chrysococcyx 



Introduction 



The genus Chrysococcyx is one of a number of genera of cuckoos 

 that are brood parasites in their reproductive habits. Their phylog- 

 eny, differentiation, dispersal, and ethology — all of which are re- 

 viewed in a comparative, yet detailed, way for the first time in this 

 paper — are of interest in themselves not only as a special "case 

 history" in the development of parasitism, but also for the light 

 they throw on the broad, general problems of evolution of parasitic 

 reproduction in the cuckoos as a family and in birds in general. 



As I pointed out in an earlier paper on Clamator (1964) the various 

 genera of parasitic cuckoos reveal divergent paths of development in 

 their mode and degree of speciahzation as parasites. Chrysococcyx, 

 for example, agrees with Cuculus in the evicting habit in the early 

 nestUng stage, a phenomenon not present in Clamator; it agrees with 

 both Cuculus and Clamator in the habit of host-egg removal by the 

 adult cuckoos from parasitized nests. Among its dozen included 

 species Chrysococcyx presents a broad range of host-parasite situa- 

 tions, from those found in species like malayanus and osculans with 

 only a very small number of regular hosts to those shown by others 

 like lucidus (plagosus), basalis, Idaas, and caprius with many dozens 

 of host species apiece. Chrysococcyx agrees more (but not rigidly) 

 with Cuculus than with Clamator in the intensity of parasitism on 

 its usual hosts, as measured by the incidence of multiple to single 

 eggs in individual nests of the latter. 



Among the most interesting and intriguing biological problems 

 exhibited by the glossy cuckoos are: 



1. The atavistic retention of courtship feeding by the adult 

 male with the correlated fledgiinghke behavior of the female; 2. the 

 still more atavistic (but not infrequent) fledgling, and even nestling, 

 feeding by adults of these parasitic breeders; 3. the tendency, def- 

 initely begun but far from perfected, toward primary differentiation 

 in host selection by sympatric species of the genus; 4. the achieve- 



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