The western capercaillie (Tetrao urogallus), also known as the Eurasian capercaillie, wood grouse, heather cock, cock-of-the-woods, or simply capercaillie , is a heavy member of the grouse family and the largest of all extant grouse species. The heaviest-known specimen, recorded in captivity, had a weight of . Found across Europe and the Palearctic, this primarily-ground-dwelling forest grouse is renowned for its courtship display. This bird shows extreme sexual dimorphism, with males nearly twice the size of females. The global population is listed as "least concern" under the IUCN, although the populations of central Europe are declining and fragmented, or possibly extirpated. The western capercaillie is one of two living species under the genus Tetrao, which also includes the lesser-known black-billed capercaillie. Etymology The word capercaillie is a corruption of the Scottish Gaelic capall coille () "Horse of the jungle". The Scots borrowing is spelled capercailzie (the Scots use of z represents an archaic spelling with yogh and is silent; see Mackenzie (surname)). The current spelling was standardised by William Yarrell in 1843. The genus name is derived from the Latin name of a game bird, probably the black grouse. The species name, urogallus, is a New Latin partial homophone of German Auerhuhn. Taxonomy The species was first described by Carl Linnaeus in his 1758 10th edition of Systema Naturae under its current binomial name. Its closest relative is the black-billed capercaillie, Tetrao parvirostris, which breeds in the larch taiga forests of eastern Russia and parts of northern Mongolia and China. Subspecies There are several subspecies, listed from west to east: T. u. cantabricus (Cantabrian capercaillie) – Castroviejo, 1967: found in northwestern Spain T. u. aquitanicus Ingram, 1915: found in the Pyrenees of Spain and France T. u. crassirostris (syn. major) C.L. Brehm, 1831: found in central Europe (Alps to Estonia) T. u. rudolfi Dombrowski, 1912: found in southeastern Europe (Bulgaria to southwestern Ukraine) T. u. urogallus Linnaeus, 1758: found in Scandinavia and Scotland (where introduced) T. u. karelicus Lönnberg, 1924: found in Finland and Karelia T. u. lonnbergi Snigirevski, 1957: found in the Kola Peninsula T. u. pleskei Stegmann, 1926: found in Belarus, central European Russia T. u. obsoletus Snigerewski, 1937: found in northern European Russia T. u. volgensis Buturlin, 1907: found in southeastern European Russia T. u. uralensis Nazarov, 1886: found in the Urals and western Siberia T. u. taczanowskii Stejneger, 1885: found in central Siberia to Altai Mountains