70 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



the latter resembles that of its parents, the former imitates that of 

 its nest-mates ..." 



POLYMORPHISM 



Two of the four species of Clamator have produced well-established 

 melanic morphs or plumage phases in restricted portions of their 

 respective ranges. These two are C. jacobinus and C. levaillantii, and 

 it so happens that the black phases of the two are extremely similar. 

 Their geographic ranges are quite dissimilar in extent, however ; that 

 of jacobinus occupies a large area of southeastern Africa, while the 

 corresponding one of levaillantii is restricted to a narrow coastal 

 strip of northeastern Tanganyika and of Kenya. 



Both of these morphs appear to be, in every way, good examples 

 of polymorphism in the sense defined by Ford (1945, p. 7d>). In his 

 definition a polymorphic species is one in which there are two or more 

 distinct phases or forms simultaneously in the same habitat, even in 

 the same deme and the same local population, and in which these 

 forms occur in sufficient numbers that even the least common of 

 them is too numerous to be accounted for by a continuous series of 

 recurrent, identical mutations. To this basic concept may be added, 

 as was pointed out by Carter (1954, p. 259) the further thought that 

 the characters of these polymorphs must be such that they do not 

 blend on crossing ; in other words, they must be controlled by single 

 genes, or at least by small groups of genes that are closely linked in 

 their mode of inheritance. Otherwise, the normal interbreeding that 

 goes on in any local population of a species would tend to transform 

 these polymorphs into a broad but continuous spectrum of variation. 

 In the case of C. jacobinus we have ample field evidence that crossing 

 between the two color morphs takes place frequently and yet no 

 intermediate plumages are known. For C. levaillantii we still lack 

 field observations of similar crossing between the morphs as little 

 work has been done in the restricted area of its polymorphism.^ In 



^As described in our discussion of migratory behavior (p. 86) Lamm noted 

 seeing two levaillantii, one in the normal and one in the black phase, at Vila 

 Luisa, southern Mozambique. There can be no reasonable doubt as to his identi- 

 fication of the pale morph, and if the two were really a "pair" this would be a 

 case suggesting that the situation between morphs in this species is the same as 

 in jacobinus. The fact that the locality is so far south of the known range of 

 the melanistic morph of levaillantii makes this sight record somewhat uncertain. 

 Furthermore, Lamm's notes are not conclusive as to whether the two birds were 

 really a pair. He merely saw a black-plumaged bird near the normal levaillantii; 

 he observed no sign of mutual interest between them, although he wrote, 

 "probably a pair." 



