346 Mr. H. Seebohm on the Birds of Natal 6fc. 



ner. The earlier writers on South-African birds regarded 

 each of these various forms as distinct species. When I 

 wrote the fifth volume of the ' Catalogue of Birds ' in the 

 British Museum, I ventured to hazard the hypothesis that 

 there were only two species, and that the intermediate 

 forms were merely crosses between the extremes. The con- 

 clusion that Messrs. Butler, Feilden, and Reid came to, was 

 that the variations are due to age, and that tbe brown birds 

 first grow black, and then (when they are six years old) grey. 

 On the underparts, below the breast, the change is still more 

 extraordinary. It is alleged that the brown changes first to 

 white, then to black, afterwards to grey, and finally to 

 whitish grey, when the bird is presumably seven or eight 

 years old. It is quite possible that this theory may be true, 

 but I am unable to discover a shred of evidence in its favour. 

 It appears to me to be a wild hypothesis, unsupported even 

 by analogy, and if true, is a unique fact in ornithology. 

 Now the theory that these variations are the result of the 

 interbreeding of two (or now that the grey birds are proved 

 to be males, of three or more) imperfectly segregated forms, 

 is supported by considerable evidence. The analogy of the 

 intermediate forms between Saxicola picata and S. capistrata, 

 between Monticola cyanusand M. so/itaria, to say nothing of 

 the distantly allied Crows ( Corvus cornix and C corone), is very 

 suggestive, and an examination of a series of each confirms 

 the theory of interbreeding. It is impossible, in either the 

 Crows or the Mountain Chats, to arrange the intermediate 

 forms in a satisfactory series. Sometimes the influence of 

 the male is apparently strongest on the upper parts, and 

 sometimes on the lower parts. It is difficult to imagine 

 that sometimes the upper parts age first, and sometimes the 

 lower parts. The facts that in the adult birds of S. leucopyga 

 the crown is white, but in birds of the year black, and that 

 in the adult birds of S. lugubris the belly is black, but in 

 birds of the year white, suggest that in the Mountain Chats 

 these parts may vary in colour with age. 



It seems to me that this vexed question is as far as ever 

 from being solved. All we can say is that the males varv 



