170 GAME BIRDS OF NORTH AMERICA. 
or else remaining motionless, evidently hoping to escape 
in that way from being seen. But if several are together 
they will usually take wing, making a great cackling 
as they rise and fly off. 
The flight of this species is firm and well sustained, 
consisting of a rapid beating of the wing's, succeeded by 
a sailing movement, and can be continued for a long dis- 
tance; but, as a rule, the birds alight after proceeding 
for a few hundred yards. The White-tailed Ptarmigan, 
like its relatives, appears to be continually in moult. It 
begins to show a few of the blackish brown vermiculated 
feathers in March, which appear very conspicuously amid 
the white plumage. The change from out the winter dress 
is effected very slowly, and the perfect summer plumage 
is not assumed until about June. In September it begins 
to change again, the feathers on the under parts being 
the first that are replaced with white ones. There is no 
regularity in this moult, as white feathers appear in 
different parts of the body after the process has once 
commenced; but it goes on so deliberately that little 
difference in the bird’s appearance is noticeable for some 
weeks, save perhaps the general hue is somewhat lighter, 
and it is quite late in the autumn—perhaps, at times, even 
the middle of winter—before the pure white dress is com- 
pleted. During all this period of changing plumage no 
two individuals are alike. The tail remains white all the 
year round, and renders the bird very conspicuous dur- 
ing the summer months. 
Although, as I have stated, it is rarely seen in the Cas- 
cade Mountains in flocks of any size, yet farther south, 
as in the mountains of Colorado, it associates in com- 
panies composed sometimes of a hundred individuals or 
more. This, however, seems to be an aggregation of 
birds mostly not fully grown, a number of broods con- 
