THE FEATHERS. 83 



the case of two species of Partridges, called the 

 Wood and Rock Partridge 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 unne- 

 cessary. 



Generally speaking, the colour of the plumage in 

 different species is the same; there are, however, 

 some constant exceptions, as, for instance, in the 

 Huffs and Reeves, in which no two birds are ever 

 found exactly alike. The Ptarmagans, again, vary 

 considerably; the Cross-beak 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 depar- 

 tures from the usual rule, of an unnatural 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 sin- 

 gular peculiarity, and we suspect that it will be 

 generally found that it extends through several gene- 

 rations 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 



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