174 
WIIITE-TATLED PTARMIGAN. 
often the means of their discovery. In this way they 
will often reach the opposite edge of the rock, and 
will, as it were, simultaneously drop off ; hut the ex- 
pectation of finding them on some lower ledge will 
be disappointed, for they have perhaps by that time 
sought for and reached the opposite side of the moun- 
tains, by a low, wheeling flight, as noiseless as the 
solitudes by which they are surrounded. The nest 
is made under the rocks and stones, and is very diffi- 
cult to be found, for the female on perceiving a person 
approach, generally leaves it, and is only discovered 
by her motion over the rocks, or lier low clucking 
cry. In winter they descend lower, but seldom seek 
the plains. 
The only other bird belonging to this interesting 
group is an American species, discovered by the ex- 
pedition under Captain Franklin. It has the habits 
of the rest, and inhabits the Rocky Mountains. It 
has been termed by Dr Richardson Lagopus leucurtis, 
or White-tailed Ptarmigan, and is at once distinguish- 
ed from any of the rest by the want of black on the 
pure winter plumage, wanting both the black eye- 
stripe and black tail, so conspicuous in the others. 
The summer dress is intermediate in colour between 
that of the rock and common ptarmigan. 
