68 U.S. NATIONAL MUSEUM BULLETIN 2 65 



with practically monomorphic eggs — and caprius, cupreus, and Haas — 

 each with polymorphic eggs. On the other hand, osculans, with a 

 single egg type, uses only a few species of fosterers, and its eggs agree 

 quite closely with those of its most favored host, Chthonicola sagittata. 

 It is to be remembered that even those species of cuckoos with ex- 

 tensive lists of known hosts tend to parasitize only a fraction of them 

 with any great regularity. 



The basic fact of polymorphism, regardless of whether it applies 

 to eggshell characters or to any other phenotypic aspect of a species, 

 would appear to be adaptive or at least would make adaptive evo- 

 lution more readily possible. In the case of brood parasites, eggshell 

 adaptation is of particular importance, but even here the resulting 

 situation is not necessarily simple to interpret. Thus, it is obvious 

 that a species of cuckoo wdth a single egg type, but using a wide 

 variety of fosterers, would inevitably come up against some whose 

 eggs its own approximated fairly closely and others whose eggs were 

 widely dissimilar. In some cases, where enough data are available to 

 establish the correlation between acceptance or rejection of parasitic 

 eggs by fosterers and the degree of egg similarity, it is clear that such 

 resemblance does confer a significant biological advantage on the 

 parasite. Examples of this are the "gentes" of the European cuckoo, 

 Cuculus canorus, and the Indian breeding population of the jacobin 

 crested cuckoo, Clamator jacobinus. Strangely enough, however, in 

 other cases lack of egg resemblance does not always appear to mitigate 

 critically against the parasites, as in the case of the jacobin cuckoos 

 breeding in southern Africa (Friedmann, 1964, pp. 20, 21). 



It follows from the above that, before we may go more deeply 

 into the problems related to egg adaptation and egg morphism, it is 

 necessary to present the data for each of the nine species of glossy 

 cuckoos vnth all pertinent details. 



1. C. malayanus: eggs are known of five of the subspecies of this 

 glossy cuckoo; in all cases they can best be described as monomorphic 

 with fairly narrow variational limits. In typical malayanus the egg 

 is dark olive-green with some small brown specks forming a wreath of 

 darkish bro\\Ti. Schonwetter (1964, p. 570) noted that such coloration 

 is the forerunner of the development of the surprising bronze tone 

 found only in the eggs of some glossy cuckoos and of some species of 

 the related genus Cacomantis. In C. m. malayanus the egg color is 

 not adapted to that of its hosts' eggs as far as the stUl meager data 

 permit a generalization. In C. m. alhijrons, Bartels (1925) found the 

 egg to be bronze colored {ex nest of Gerygone sulphurea). In C. m. 

 poeciluruSf Schonwetter described the eggs as uniform yellowish olive- 

 bro^vn or greenish olive-bro^vn, somewhat darker, more bronze than 

 in C. lucidus plagosus. In C. m. russatus the egg varies from pale to 



