PARASITIC WEAVE RBIRDS 11 



It is noteworthy that Vidua Jischeri appears to be almost wholly 

 sympatric with V. hypockerina. They are, as sympatric species 

 should be, completely distinct and show no tendency to cross. I 

 think that they were not originally wholly synchronic as well as 

 sympatric, but that the blue widow bird, V. hypockerina probably 

 antedated the evolution of V. Jischeri. V. macroura was probably 

 next in the line of viduine differentiation. The conclusion rests upon 

 the fact that its juvenal plumage resembles that of the combassous 

 and of V. hyiwcherina, and upon its wide distribution, which allowed 

 for geographic contact with these forms. V. macroura or the stock 

 of which it is the living representative later gave rise to V. regia in 

 the southwestern part of Africa and to V. Jischeri in the northeastern 

 part. All are of sufficient antiquity to have allowed intermediate 

 stages to disappear long ago. Thus we have the peculiar situation 

 where the archaic, ancestral stock, subgenus Hypochera, comprises 

 three closely similar species in which the degree of differentiation 

 (to human eyes at least) is hardly more than what is found in sibling 

 species, while the derivative line, subgenus Vidua proper, com- 

 prises four species that are very distinct and dissimilar in the adult 

 male nuptial plumage but are much less dissimilar in all other stages. 



In his discussion of the problem of sibling species Mayr (1948, 

 p. 231) noted two seemingly feasible explanations. One was that 

 such species are of such recent origin as to preclude the acquisition 

 of pronounced morphological differences, an explanation assuming 

 that reproductive isolation is acquired through very few steps and 

 that, consequently, such species are still genetically very similar. 

 According to the other explanation, the slight morphological char- 

 acters involved are genetically firmly integrated so as not to become 

 visibly affected by the mutational steps that have produced the 

 ecological and reproductive isolating mechanisms. The combassous 

 seem to be accounted for more adequately by the second of these 

 two explanations. The combassous are old enough to be the ances- 

 tors of the long-tailed widow birds, but there is no direct or even 

 implied evidence that causes me to consider the evolutionary history 

 of the combassous as of relatively short duration when compared 

 with that of the long-tailed members of the genus Vidua. 



Of all the long-tailed species of Vidua, the shafttail, V. regia, seems 

 most likely to be closest to the stock from which evolved the paradise 

 widow bird, Steganura paradisaea. This conclusion is based on the 

 fact that the shafttail shows greater similarity in coloration and also 

 has the tendency for the elongated rectrices to broaden; while ad- 

 mittedly not the most convincing evidence, it is more than may be 

 seen in any of the other existing species of Vidua. While Steganura 

 would thus seem to be a relatively recent development in the Viduinae, 



