AVIAN GENUS CHRYSOCOCCYX 79 



tion in egg size, permitting the bii"d to use hosts much smaller than 

 itself, is only conjectural, but the fact remains that the bird does use 

 chiefly small passerine species as fosterers. While the glossy cuckoos 

 do not exhibit such strildng egg reduction, they do lay eggs that are 

 fairly small in relation to their body size, which may be of adaptive 

 value in approximating the size of the eggs of some of their frequent 

 hosts. For example, the body size of C. hasalis is much greater than 

 that of the species of Malurus that it parasitizes, but the eggs of the 

 two are very similar in dimensions. Again, the egg of the African 

 yellow-belhed emerald cuckoo, C. cupreiLS, is sm-prisingly light in 

 weight, almost as light as eggs of the two much smaller Asiatic species, 

 C. maculatus and C. xanthorhynchus; the full egg weight is 1 .43 grams 

 in cupreus, 1.37 grams in maculatus, and 1.40 grams in xanthorhynchus, 

 whereas the dimensions of the eggs are 17.8-20.5X12.2-13 mm. in 

 cupreus and only 15.1-18X11.2-13.3 mm. in the two Indian species. 

 The body size and weight of cupreus exceed the figures for maculatus 

 and xanthorhynchus by approximately 40 percent. The eggs of these 

 two very small species of Chrysococcyx were compared by Burton (1935, 

 p. 276) wdth those of two Indian species of Cuculu^, poliocephalus and 

 saturatus. His residts emphasize the difference in extreme egg reduc- 

 tion in these species of Cuculus and in Chrysococcyx, as he was led to 

 write of the little Asiatic emerald cuckoo, C. maculatus, that its "eggs 

 are very large for cuckoo's eggs, in proportion to the size of the bird, 

 the bulk being as much as it is in the eggs of poliocephalus . . . and 

 saturatus . . . birds of, perhaps, between three and four times the 

 cubic contents of the tiny Emerald Cuckoo." 



The largest and heaviest eggs of all the glossy cuckoos are those of 

 osculans and caprius. This is in agreement with their larger body size, 

 but if Schonwetter's figures are correct, the egg weight in C. caprius 

 is 6.2 percent of the body weight, while in C. lucidus plagosus, a much 

 smaller egg and bird, the egg weight is 7.9 percent of the body weight. 



Although in some cases there may be selective value in approximate 

 size agreement in the eggs of the parasite and of the host, this does 

 not always operate on a critical level. Thus, in New Zealand, the 

 little gray warbler, Gerygone igata, a bird that lays an egg about 18 X 

 12.5 mm., is parasitized by two very dissimilar cuckoos, the nominate 

 race of the bronze cuckoo, Chrysococcyx lucidus, which produces an egg 

 of very similar size, and the larger, very different, long-tailed cuckoo, 

 Urodynamis taitensis, that lays an egg about twice as long and twice 

 as broad (32 X 27 mm.). 



The recent experimental work of Tinbergen (1951, p. 45; 1954, pp. 

 246-247) has shown that discrepancy in size does not deter an egg's 

 acceptance by many birds. In fact, he found that the unusually great 

 size of some of the egg models used had the effect of increasing the 



