1926] Swarth: Birds and Mammals from the. Atlin Region 91

willow ptarmigan frequented the floor of this valley and the lower slopes of the surrounding mountains. Their preferred habitat was a tangle of low willow and birch brush, with grassy open patches at intervals. None was seen on the higher ridges or the slopes higher than about 4000 feet; there this species was replaced by the rock and the white-tailed ptarmigans.

On September 1, a trip was made to ‘‘Blue Cafion,’’ a local name for a section of upper Spruce Creek some twelve to fifteen miles south- east of Atlin. Willow ptarmigan were then beginning to gather in large flocks. In the valley bottom relatively few birds were seen, though some were scattered all through this section, too; the center of abundance was on the lower slopes of the mountains, at from 3500 to 4000 feet. This was above the more extensive tangles of willow and trailing birch, and was a much more open sort of country. Thickets of dwarfed balsam, and some of willow and birch, were interspersed with open stretches, grass-covered or carpeted with Empetrum and other low-growing shrubs.

Willow ptarmigan, in flocks of from ten or twelve (single families, presumably) up to sixty or seventy, were within sight or hearing prac- tically all of the time that we remained at that level. The larger flocks were, I was told, the first indication of much greater gatherings that were assembled during the winter months. On this date (Sep- tember 1) specimens were taken of adults and young of both sexes.

Adult males taken in midsummer (June 30) in the breeding plumage retained a great deal of white on the belly, and these old white feathers apparently remain until replaced by white feathers at the end of August. Adult males taken September 1 are mostly white on the lower breast and abdomen. Adult females are mostly in the reddish ‘‘winter plumage, preliminary,’’ to use the descriptive phrase originating with Dwight (1900), though always with many barred feathers of the breeding plumage persisting on breast and flanks, and some blackish feathers of the same plumage on the back. Over the whole belly the molt in every specimen examined was direct from the barred breeding plumage to white winter garb. There is an adult female of alexandrae at hand (Willett coll., Prince of Wales Island, Alaska, September 23, 1919) in the reddish post-breeding plumage, with but a few scattered barred feathers left. I have seen none from the interior that has assumed this plumage so nearly in its entirety. In the Atlin region it is evident that the white winter plumage begins to come in before the reddish ‘‘winter plumage, preliminary’’ is more than half acquired.