Many observers have assumed that there are two moulting seasons--the first, which occurs in autumn, extends to the whole of the feathers; during the second, which takes place in spring, the smaller feathers alone are changed; but the winter clothing does not immediately replace the summer dress, nor does that at once supersede the winter suit. On this account it has been supposed by some that the Ptarmigan moults four times in the year. American observers, on the contrary, think they have perceived that the smaller feathers at least are not replaced, but simply changed in colour. According to Richardson, "The second change is occasioned, not by the reproduction of feathers, but by the coloured ones becoming white, the process commencing on their tip. This alteration takes place in scattered feathers, which at the same time lengthen, and in a week or ten days the change is complete; spotted specimens undergoing the change may be distinguished from spring ones by the worn state of the tarsal feathers." This Ptarmigan is spread throughout the northern parts of both the New and Old World, although it is not found everywhere in the same numbers. It is very plentiful in Scandinavia, and also in Finland, and Russia, and common in the eastern coasts of the latter country, and in many parts of Siberia. Radde did not meet with it about the Lake of Baikal or the Amur, and therefore concludes that it does not stay there during the summer; but he found it in Eastern Sayan, at a height of between five and six thousand feet above the sea-level, on wide plains, overgrown with birch bushes. It breeds in the valleys of the Rocky Mountains, and upon the arctic coasts; but collecting in flocks on the approach of winter, it retires southward as the severity of the weather increases. Considerable bodies, however, remain behind, even in the coldest winters. In the year 1819 its earliest appearance at Cumberland House, latitude fifty-four degrees, was in the second week in November, and it returned to the northward again before the beginning of spring. [Illustration: THE WILLOW PTARMIGAN (_Lagopus albus_). ONE-THIRD NATURAL SIZE.]