1907] Beebe: Geographic Variation in Birds. 17 



I know of no definite experiments which have been carried 

 out in respect to the plasticity of pigment supply in the epidermis 

 of birds of any species ; hence the results, interesting and signifi- 

 cant as these are, of the few experiments I have undertaken, 

 must be considered only as tentative until they receive further 

 confirmation from future experiments by myself or by others. 



Paralleling in many ways the results of my experiments on 

 Scardafella, is the relationship between the yellow-rumped and 

 the chestnut-breasted finches Munia flaviprymna and Munia cas- 

 taneithorax, two members of the family Ploceidae or weaver- 

 birds inhabiting Australia. Mr. D. Seth-Smith discusses this in 

 an interesting article in a recent number of the Avicultural Mag- 

 azine. There is little doubt but that these two birds are closely 

 related, since their songs are exactly alike and the young, until 

 three weeks old, are indistinguishable. The adults, however, are 

 radically unlike in coloring, especially as regards the head and 

 under parts. In M. flaviprymna these portions are pale creamy- 

 buff, while in M. castaneithorax the sides of the face, ear-coverts 

 and throat are blackish, the sides of the neck and body, fore 

 neck and chest pale cinnamon, followed by a black band across 

 the breast. Below this the plumage is white. 



In captivity, specimens of M. flaviprymna two or three years 

 of age have been known to assume gradually the markings of the 

 darker species. It was observed of one individual after its fall 

 moult, "the throat had darkened considerably and there were 

 very distinct traces of a dark pectoral band." These birds 

 were at first thought to be hybrids, but as the young of M. cas- 

 taneithorax shows traces of the chestnut beast when only six 

 weeks old and is indistinguishable from its parents at six months, 

 the age of the individuals which assumed the new coloration 

 would alone serve to disprove such a theory. 



In summing up his conclusions on this significant change of 

 plumage in captive birds, Mr. Seth-Smith says, "My own theory 

 is, that M. flaviprymna is merely a desert form of M. castanei- 

 thorax which, to fit it for its desert life, has gradually lost the 

 conspicuous markings of the latter. The changed conditions of 

 a life in captivity and a more humid atmosphere, however, cause 

 it, to a certain extent, to reassume the markings which it has lost 

 on account of its desert life. Of course only a very few exam- 

 ples, perhaps not more than one per cent., ever do change color. 

 Whatever the true explanation of the change may be, it seems to 

 me that the two forms are not distinct species, but only local 

 races, and in classification are only entitled to be ranked as sub- 

 species." 



