The largest and most numerous of North America's 3 species of ptarmigan, the Willow Ptarmigan is a characteristic feature of arctic, subarctic, and subalpine tundra. This species has developed a variety of behavioral and physiological adaptations for living in extreme northern environments, where temperatures and light levels vary dramatically and predators abound: feathered tarsi that function as snowshoes, use of snow burrows for shelter, and a complex pattern of molting that results in cryptic plumage year-round. Both the Willow Ptarmigan and its congener the Rock Ptarmigan (Lagopus muta), have Holarctic distributions; they are the only 2 grouse species with a circumpolar distribution.
Willow Ptarmigan are usually monogamous, but 5–9% of males may be polygynous. Unusual for grouse, pairs remain together from the beginning of the breeding season until their chicks are independent. This is the only grouse in which the male is regularly involved in parental care.
Field studies of the conspecific Red Grouse (Lagopus lagopus scoticus) in Great Britain and Willow Grouse (L. l. lagopus) in continental Europe conducted during the past century have yielded comprehensive information on the life history and behavior of the species, in addition to substantive contributions to wildlife population dynamics and life history theory ( Jenkins et al. 1963 , Watson and Jenkins 1964 , Cramp and Simmons 1980a , Pedersen et al. 1983 ). Unlike its wily European counterpart, the Willow Ptarmigan in most of North America (with the exception of Newfoundland) is relatively tame and may be observed and captured readily. Population dynamics studies began more than 30 yr ago in Newfoundland ( Peters 1963b , Mercer 1967b , Bergerud Bergerud 1970a , Bergerud 1970b ) and in Alaska (Weeden Weeden 1965c , Weeden 1967 ). Studies on bioenergetics, nutrition, and biogeographic variation were conducted in Alaska (West and Meng West and Meng 1966 , West and Meng 1968 , Irving et al. Irving et al. 1967a , Irving et al. 1967b , West West et al. 1968c , West 1972 ). Since 1980, multiyear studies of behavior, mating systems, reproductive ecology, and fitness of individuals have been conducted in northwestern British Columbia (Hannon Hannon 1983 , Hannon and Smith 1984 , Martin and Hannon 1987 , Mossop 1988 , Hannon and Martin Hannon and Martin 1992 , Hannon and Martin 1996 ); near Hudson Bay, Manitoba (Martin Martin 1984b , Martin 1991a , Martin and Cooke 1987 , Martin et al. 1989 ); and in Ontario ( Thomas 1984b ). Much remains to be learned, however, about migration patterns, scale of dispersal, and life history differences among subspecies.