34 GALLING 



are thrown off; but there is no general moult in the feathers 

 at that season, and probably not at any season, the moult 

 being gradual, just as the shedding of leaves is upon some 

 evergreen trees. In winter, these birds congregate in family 

 parties or packs, live peaceably together, and shelter them- 

 selves in holes in the earth or in the snow, through which last 

 hey contrive to scrape down till they arrive at the scanty 

 vegetation which it covers. At the commencement of sum- 

 mer (for in their haunts spring is a season of snows), that is, 

 usually about the month of June, they disperse in pairs 

 (they are monogamous), a little further down the mountain 

 than their winter haunts, and there scrape a circular nest, in 

 which the eggs, varying from six to twelve, or fifteen, the 

 average being about ten, are deposited. The young are 

 covered with down, which bears some resemblance to the 

 general tint of the summer plumage, but is less mottled, and 

 lighter in the tints. The eggs also partake of an admixture 

 of the same colours. 



That the autumnal change of colour in the ptarmigan, and 

 probably also the summer change, is a change in the same 

 feathers, and not the effect of a moult, is proved by many 

 circumstances. In the first place, the birds have more pow- 

 erful flight during the time that the change is taking place, 

 than at any other period of the year. In the second place, 

 two moults at least would be necessary ; for, with the excep- 

 tion of the ear-coverts, the prevailing tint of the whole bird 

 is grey in autumn, and brown in summer. Thirdly, the 

 decay first of the brown, and then of the grey, is gradual 

 over the whole bird. Fourthly, the change to white is 

 complete, in proportion as the place and the season are cold. 



The plumage of the ptarmigan is thus a sort of natural 

 thermometer ; and as the plumage becomes a bad conductor 

 of heat in proportion as it whitens, and the evaporating 

 power of the air diminishes with the cold, it is probable that 



