AVIAN GENUS CHRYSOCOCCYX 103 



is that this atavism is more widespread in the former, where it has 

 been noted m 4 out of 12 species, than in the latter genus, where only 

 1 out of 12 included species has been observed to exhibit this tendency. 

 Inasmuch as Eudynamis and Scythrops are monotypic, comparisons 

 with them are meaningless. Cacomantis is still too imperfectly known 

 to yield significant comparisons here. If the present absence of 

 fledgling feeding is to be interpreted as being due to its elimination 

 during the past history of each species and, conversely, if its presence 

 is taken to imply the opposite, the difference noted above for Chryso- 

 coccyx and Cuculus may be taken as an indication that the glossy 

 cuckoos, as a group, are not as advanced as Cuculus in their develop- 

 ment of brood-parasitism. 



It may be mentioned that only a single instance of this type of 

 behavior has been reported for a single species of cowbird (Friedmann 

 1963, p. 27, ex Walton 1903) and none for any of the other groups of 

 parasitic birds, honey-guides, weavers, or ducks. 



Summary and conclusions 



The glossy cuckoos, forming the genus Chrysococcyx, are the 

 smallest members of their family, and by virtue of their small size 

 and their glossy, "metallic" plumage are a natural assemblage, 

 closely related to, but distinct from, other genera of the Cuculmae, 

 especially Cacomantis and Cuculus. They probably originated in the 

 Australo-Malaysian area, possibly in Pliocene time, from the stock 

 represented today by the other two genera mentioned above or at 

 least from the common stock that also gave rise to them. All three of 

 these genera are very similar in their structure, in their habits, and 

 particularly in many details of their brood parasitism. While Cuculus 

 has come to occupy a much more extensive part of the earth's land 

 surface than the other two and, in one of its species, Cuculus canorus, 

 has come to develop a degree of adaptive specialization unknown in 

 the other two, Chrysococcyx also experienced a greater geographical 

 and speciational expansion than has Cacomantis and it has come to 

 occupy a niche in its parasitism on small passerine bkds in some parts 

 of the world — such as Africa, New Zealand, and some of the islands 

 of the South Pacific, where it is largely aUoxenic with respect to 

 other cuckoos — as well as to flourish in other places — such as Australia 

 and southern Asia, where it is partly homoxenic with members of 

 both its related genera. 



Two new terms, alloxenia and homoxenia are proposed to facilitate 

 thmking and discussion of brood parasitism. Alloxenia, with aUoxenic 

 as its adjective, implies that different species of parasites use different 

 hosts, while homoxenia, with homoxenic as its adjective, conveys 



