closely related rock ptarmigan (Lagopus muta) by its larger size and thicker bill and by the fact that it is not generally found above the tree line while the rock ptarmigan prefers more elevated, barren habitat. The summer plumage is browner and in the winter, the male willow ptarmigan lacks the rock ptarmigan's black stripe between the eyes and bill. The white-tailed ptarmigan (Lagopus leucura) in North America is smaller, has a white tail and finely-barred greyer plumage and lives permanently above the tree line. The distinctive British Isles subspecies L. l. scoticus (red grouse) was once considered a separate true British species but is now classified as a sub-species. This moorland bird is reddish brown all over, except for its white feet. The voice is low-pitched and guttural and includes chuckles, repeated clucking sounds, and expostulations. When displaying, the male makes rattles and barking noises. Taxonomy and systematics The willow ptarmigan's scientific name, Lagopus lagopus is derived from Ancient Greek () 'hare' + () 'foot', in reference to the bird's feathered feet which allow it to negotiate frozen ground. Subspecies Nineteen subspecies have been recognised though some are believed not to be valid. Most differ little in appearance, though the red grouse (L. l. scoticus) is rather distinct. The taxonomy is confused, partly because of the complicated changes in plumage several times a year and the differing colour and pattern of the summer plumage: hibernicus (Latham, 1787) - Ireland scotica (Latham, 1787) - Britain variegatus Salomonsen, 1936 - Trondheim, Norway lagopus (Linnaeus, 1758) - Scandinavia, Finland and North European Russia rossicus Serebrovsky, 1926 - Baltic countries and Central Russia birulai Serebrovsky, 1926 - New Siberia koreni Thayer & Bangs, 1914 - Siberia maior Lorenz, 1904 - Southeast Russia, North Kazakhstan and Southwest Siberia brevirostris Hesse, 1912 - Altai Mountains and Sayan Mountains kozlowae Portenko, 1931 - West Mongolia sserebrowsky Domaniewski, 1933 - East Siberia kamtschatkensis Momiyama, 1928 - Kamchatka and Kuril Islands okadai Momiyama, 1928 - Sakhalin Island muriei Gabrielson & Lincoln, 1959 - Aleutian Islands and Kodiak Island alexandrae Grinnell, 1909 - Alaska and British Columbia alascensis Swarth, 1926 - Alaska leucopterus Taverner, 1932 - Arctic islands of North Canada albus (Gmelin, 1789) - North Canada ungavus Riley, 1911 - North Quebec and North Labrador alleni Stejneger, 1884 - Newfoundland The willow ptarmigan often hybridises with the black grouse (Tetrao tetrix) and the hazel grouse (Tetrastes bonasia) and