NO. 4 AVIAN GENUS CLAMATOR — FRIEDMANN 7I 



this connection it may be recalled that Stresemann (1947, pp. 518- 

 519) suggested that the ". . . allele-producing mechanism has besides 

 some physiological effect increasing viability in this special environ- 

 ment (but not elsewhere) which results in its being favoured by 

 selection . . ." In support of this suggestion he pointed out that a 

 shrike, Laniarius ferrugineus sublacteus, also has a melanistic morph 

 (L. nigerrimus) in the same limited area of coastal Kenya and the 

 lower portion of the valley of the Tana River. 



While the restricted geographic coincidence of melanistic poly- 

 morphism in two widely dissimilar and unrelated birds as a cuckoo 

 and a shrike may be suggestive, it remains that in neither species do 

 we have as yet any observational data as to the relative abundance 

 of the two plumages, to say nothing of the frequency of crossing 

 between their phases. In the absence of such information we can only 

 interpret the situation in C. levaillantii as probably similar to what 

 we know in the related C. jacobinus in southeastern Africa, and in 

 that species it is difficult to see that either morph has any selective 

 advantage over the other. In connection with Stresemann's sugges- 

 tion, it may be recalled that C. jacobinus also occurs in coastal Kenya 

 and the Tana Valley, and has produced no melanistic morphs there 

 although it has done so far to the south. If there were something 

 in the ecological situation of coastal Kenya that might favor such 

 melanisms we might expect it to have produced some visible mani- 

 festation in C. jacobinus as well. That local ecology is not directly 

 important in the establishment of polymorphism is further indicated 

 by the fact that in the extensive area of southeastern Africa where 

 jacobinus has two phases, levaillantii occurs in a single, "normal" 

 or "pale" phase. In other words the two species are sympatric in the 

 two areas where one and not the other is polymorphic. 



The melanistic morph of C. jacobinus occurs as a breeding form 

 throughout Natal, the eastern Cape Province, the eastern half, or 

 more, of the Transvaal, the Orange Free State, and to Bechuanaland 

 (Mahalapye), Southern Rhodesia (Bulawayo), Northern Rhodesia 

 (Livingstone), and Nyasaland (Misanje). It is decidedly rare in 

 the Rhodesias and Nyasaland, and finds its greatest abundance in 

 Natal, the eastern Cape Province, and eastern Transvaal. It also 

 occurs in southern Mozambique, but I know of but one actual speci- 

 men record from there, and it had no exact locality other than 

 "Mozambique" on its label. 



The corresponding black phase of C levaillantii is known, as far 

 as I have been able to learn, from some 26 specimens in the museums 

 of the world. Of these, no fewer than 18 were collected within 50 



