Page:The Zoologist, 4th series, vol 6 (1902).djvu/302

252 their lives, owing to disease of the ovary, and it is probable that birds in captivity (which certainly live longer, when properly treated, than birds at liberty) are more subject to that disease than when they are free. This would be a more probable solution of the late assumption of the blue-black plumage by Mr. Souëf's birds than the conclusion that the Satin Bower-bird only assumed its black clothes to die in. The wedding garments of birds are believed to be assumed for the subjugation of the hens, and birds do not wait until they are old before they begin to breed.

There is no doubt that albinism in birds is due to constitutional weakness, and is a frequent result of close inbreeding. If a pair of Sparrows (Passer domesticus) takes up its quarters in one part of a building, or in the roof of an isolated cottage, the young, inbreeding for successive generations, are pretty certain to throw individuals with more or less white in the plumage. The White Dove (popularly known as "White Java") is known to be merely the albino form of the Collared Turtle (Turtur risorius), and Mr. Abrahams assured me that it could always be produced by close inbreeding from the common type. It is probable that inbreeding first produced the pied Java Sparrows, from which the Chinese, by careful selection, evolved the white variety of that species. White in the plumage of birds is frequently due to old age, and increases year by year. A Chaffinch which I had for about fifteen years acquired quite white eyelids before its death, and a Cordon-bleu (Estrilda phœnicotis), now in my possession, began to acquire a white wing-speculum some three or four years ago; this has now become a large white patch. A pied Chaffinch, which I once caught in the garden, became much whiter at the two succeeding moults; and a pied Blackbird sent to me a year or more ago showed an increase of white after its autumn moult; both were delicate birds, and did not live long, so that I conclude they were probably inbred.