20 U.S. NATIONAL MUSEUM BULLETIN 2 65 



bridges the gap between them to the extent that the evolutionary- 

 history of klaas requires little imagination to unravel. 



The two remaining species, caprius and cupreus, are very different 

 from each other. The former is a common, widespread bird of the open 

 bush and tree-dotted grasslands, and the latter is much more of a 

 forest dweller. As we have already seen from van Someren's tabulation 

 of characters and also from Berger's (1955) internal anatomical 

 studies, cupreus is closer to klaas than to caprius, which is rather 

 divergent from both. In an evolutionary sense, however, neither 

 poses any real difficulties of interpretation. They are both "climax" 

 species of the African section of the genus, just as in their ways 

 meyerii and rujicollis are in New Guinea and osculans is in the drier 

 parts of Australia. 



Furthermore, it may be pointed out that the plumages of the 

 young birds and of the adult females of the African klaas, cupreus, and 

 caprius are fairly similar in general pattern to those of corresponding 

 stages of the Asiatic maculatus. The yellow-bellied emerald cuckoo, 

 C. cupreus, has become differentiated into four geographic races; 

 the didric cuckoo, O. caprius, has remained monotypic. Both have 

 migratory populations m southern Africa and resident ones (as far 

 as we know) in equatorial Africa. 



To round out this discussion of plumages it may be noted that the 

 genus Chrysococcyx reveals a tendency to produce rufescent coloration, 

 both as a part of the normal plumage patterns of many of its com- 

 ponent species and also as an occasional, complete color phase. 

 Rufescent or hepatic plumage phases occur in different degrees of 

 frequency in a number of genera of cuckoos. This plumage, however, 

 has been found only in immature birds and has been described in the 

 European cuckoo, Cuculus canorus canorus, by many authors. It also 

 occurs in the closely related yellow-biUed cuckoo of Africa, Cuculus 

 canorus gularis, but has not been noted in the other African species of 

 the genus (solitarius and cafer) or in the Australian Cuculus pallidus. 

 Enough examples of these three species have been preserved in 

 collections to make the absence of an hepatic phase a well-established 

 fact. I am not aware of such a rufescent plumage in the young of the 

 Asiatic species of Cuculus, but here further search may reveal it. 



In the genus Cacomantis rufescent plumage is the regular, not the 

 unusual or sporadic coloration. In view of the close phylogenetic 

 connection between it and Chrysococcyx, it is suggestive to find this 

 trend well developed there. It is possible to think of this situation as a 

 basic one from which the occasional rufescent tendencies of the 

 glossy cuckoos may have stemmed. 



In the glossy cuckoos an hepatic plumage has been noted in two 

 species, the violet cuckoo, C. xanthorhynchus, and the didric, C. 



