THE FEATHERS. 67 



of North America, which in winter burrow underneath the 

 snow, a still warmer covering is provided, the growth of 

 feathers being actually doubled; so that they have nearly 

 twice as warm a coat when they most require it, as they had 

 during summer when it was unnecessary. 



Generally speaking, there is little or no variety in the colour 

 of the plumage in each species ; there are, however, some con- 

 stant exceptions, as, for instance, in the Kuffs and Eeeves, in 

 which no two birds are ever found exactly alike. The Ptar- 

 migans, again, vary considerably; the Crossbill also has the 

 same peculiarity, and it is almost needless to point out the 

 constant variety observable in our common barn-door fowls ; 

 but, exclusive of these, which may be called natural variations, 

 there are occasional departures from the usual rule of an un- 

 natural character. Thus Blackbirds are not unfrequently 

 found very considerably mottled with white. Woodcocks are 

 now and then shot of a delicate and uniform fawn colour. 

 We have also seen white Swallows, and a few other small 

 birds ; and amongst Crows and Rooks, one or two interlopers 

 may be occasionally observed with more or less white feathers 

 peeping out from their glossy wings. Closer observations may 

 probably throw additional light upon this singular peculiarity, 

 and we suspect that it will be generally found that it extends 

 through several generations of birds reared by the same pair. 

 In one instance we know, indeed, that this was the case. A pair 

 of Rooks were in the habit of building in a wild spot near Ruthin, 

 where there were few trees affording shelter for others. The 

 attention of the tenant on the farm was soon attracted by the 

 singular appearance of two white young ones, and, to his sur- 

 prise, for three or four years, the same phenomenon occurred, 

 two white Rooks being the invariable and sole nursery establish- 

 ment of this solitary sable pair of old birds. A change of 

 plumage has also been observed to take place occasionally by 

 limiting the bird to a particular sort of food ; thus bird-fanciers 

 say, that by the use of hemp-seed, Bullfinches and some other 

 kinds of birds will frequently assume a darker colour. 



