AVIAN GENUS CHRYSOCOCCYX 77 



There is a close agreement in size between didric eggs (average 21.7 

 X 14.9) and those of the red bishop (average 20.5 X 14) and of Cape 

 sparrow (average 19 X 14 mm.). However, not infrequently the cuckoo 

 eggs are larger than even these host eggs in the same nest. Thus, 

 Markus (1964, p. 123) found a large didric egg, 25 X 14.5 mm., in 

 a red bishop's nest and another measuring 23.7 X 14.3 mm. in another 

 nest of the same species. 



The eggs of the didric cuckoo vary in length from 21 to 25 mm. and 

 in \\-idth from 13.8 to 17 mm.; the largest ones seen by me or recorded 

 in the Hterature were 24.8 X 16.5; 24.3 X 17; 25 X 15.5 mm.; the 

 smallest ones were 20.8 X 14.2; 21.1 X 14.5; 21.2 X 14.3 mm. Didric 

 cuckoo egg measurements tabulated by Schonwetter (1964, pp. 536, 

 586) are as follows: length 21.5 mm.; width 14.8 mm.; weight of the 

 empty shell .19 grams; thickness of the shell 0.095 mm.; weight of the 

 full egg 2.55 grams; relative weight of the shell to that of the full egg 

 7.4 percent; body weight of the bird 40 grams; relative weight of full 

 egg to body weight of the hen 6.4 percent. 



To sum up the foregoing data, we may note that egg monomorphism 

 is characteristic of those species of Chrysococcyx found in the Australa- 

 sian portion of the range of the group, which are also, at least in the 

 present reconstruction of their history, nearer to the older stock of the 

 genus- — malayanus, lucidus, basalts, and osculans. In tlie two Asiatic 

 species, maculatus and xanthorhynchvs , the still meager evidence sug- 

 gests polymorphism, while in the thi'ee African "climax" species, 

 caprius, cupreus, and Haas, the eggs are definitely polymorphic. 



In the monomorphic egg-laying species the foUo\\ing specific 

 differences should be noted. In the case of malayanus there appears to 

 be some slight geographic, subspecific variation in egg coloration, but 

 not much within each racial entity, merely the range of color implied 

 in such descriptions as "j^ellowish olive-browTi to greenish olive brown," 

 or "sometimes slightly freckled." In lucidus and in osculans there is an 

 easUy rubbed oft', superficial i)igment, but the adaptive value of this 

 color is not dependent on its durability or removabilit};'; in fact in 

 lucidus there is no evidence that it is host-egg adapted before or after 

 alteration, while in osculans it is highly adapted to its main host prior 

 to any color loss and such loss occurs, if at all, after the critical period 

 of acceptance or rejection b}^ the host is past. Such discoloration 

 probably occurs, although seldom in nests undisturbed by man, as the 

 eggs must be rubbed to produce it. In hasalis some degree of resem- 

 blance exists to the eggs of some of its hosts but not to those of others. 



In the polymorphic egg producers of India, maculatus and 

 xanthorhynchus , we find a range of host-egg similarity from very close 

 to only fair or moderate. Coming to the African species, klaas shows 

 no egg resemblance to those of many of its hosts and not more than 



267-562—68 7 



