What is "lagopus mutus"

Ptarmigan \Ptar"mi*gan\, n. [Gael. tarmachan; cf. Ir. tarmochan, tarmonach.] (Zo["o]l.) Any grouse of the genus Lagopus, of which numerous species are known. The feet are completely feathered. Most of the species are brown in summer, but turn white, or nearly white, in winter.

Note: They chiefly inhabit the northern countries and high mountains of Europe, Asia, and America. The common European species is Lagopus mutus. The Scotch grouse, red grouse, or moor fowl ( Lagopus Scoticus), is reddish brown, and does not turn white in winter. The white, or willow, ptarmigan ( Lagopus albus) is found in both Europe and America.