VARIATION 309 



The absence of colour, it is to be remarked, does not affect 

 the pattern of the feathers. In white Peacocks, for example, all 

 the characteristic markings can be traced. 



Frequently birds which assume a white dress gain their 

 normal plumage at the next moult. On the other hand, some 

 white varieties appear to be congenital, and, moreover, to turn 

 up in the offspring of normally coloured birds through succes- 

 sive generations. 



The Hon, Walter Rothschild, who has paid much attention 

 to this subject, has given some interesting illustrations of this. 

 Thus, in the summer of 1891 four white Swallows {Hirundo 

 rustica) were hatched in the town of Aylesbury, and were 

 allowed to escape. In 1 892 the same pair of birds reared one 

 white bird out of an otherwise normal brood ; in 1893 they 

 produced two white, and three normal young; and in 1894 

 two white young — -male and female — and two normally coloured 

 birds. Another nest in 1894, in the same town, also contained 

 two white young (females) and two or three normal birds. 

 The parents of these, Mr. Rothschild suggests, were probably 

 related to the first pair. In 1895 this pair produced two broods, 

 the first consisting of three white and two normally coloured 

 birds, which all flew away on 29th June, the second of one 

 white bird — a female now in the Tring Museum — and four 

 normal birds. 



That certain birds have a predisposition to beget white 

 young is further illustrated by the case of a nest of four Wheat- 

 ears taken at Lakenheath, Suffolk, all of which were white. 



By way of contrast to these cases of pigment atrophy we 

 have instances of melanism — intensification of pigment pro- 

 ducing black, or nearly black varieties. One of the best in- 

 stances of this is perhaps that furnished by that curious variety 

 of the Common Snipe known as Sabine's Snipe described on 



p. 301- 



While so far it has been found impossible to produce white 

 varieties, this is not the case with melanistic and other colour 

 variations. Bullfinches, as is well known, become black if fed 

 on a diet of hemp-seed. 



With black varieties, as in cases of pigment atrophy, the 

 characteristic pattern of the feathers is preserved by each 

 species, though this is often visible only in certain lights. 



