Systematics

Geographic Variation

Little genetic differentiation among birds sampled in Alaska, Canada, and Norway suggests substantial gene flow among those populations. Gyrfalcons in Greenland and Iceland, however, appear genetically distinct (Johnson et al. 2007).

Complete gradation among plumage colors, though most birds are lumped into one of three color variants for convenience (white, gray, and dark). Relative frequency of each color variant differs among locations, and variants not present in all areas. Birds from n. Greenland and Canadian Arctic Islands mostly white; birds from central and s. Greenland semi-white (sometimes called “silver”), gray, or dark; birds from n. (mainland) Northwest Territories roughly 50% white, 50% gray; birds from n. and nw. Alaska range from white (5-10%, P. Bente pers. comm.) to dark, but mainly gray; birds from other parts of range predominately gray. Darkest birds found primarily in Labrador, Quebec, and s. Greenland (Salomonsen 1950, Cade 1960, 1982, Bromley 1986, Poole and Bromley 1988b).

Regional prevalence of color variants (particularly white and intermediate plumages) possibly related to climate, as reflected by isotherms and temperature of oceanic currents rather than latitude; white types more common in colder areas (Salomonsen 1950, Ellis et al. 1992). Dark birds of Labrador and Quebec suggested as descendant of southern population isolated from more northerly refugium where white birds differentiated, while intermediate types persisted in separate southern refugia during Pleistocene (Palmer 1988, Ellis et al. 1992, Cade in Flann 2003). However, recent genetic analyses suggest Gyrfalcons may have expanded from only one refugium and that genetic differentiation was caused by genetic drift and philopatry (Johnson et al. 2007). Complete understanding of factors that caused and maintain geographic trends in plumage color is still lacking.

Outside North America, few white variants in n. Europe but increasing in proportion eastward to ne. Siberia and Kamchatka where approximately 50% are white (Dementiev and Gladkov 1957, Ellis at al. 1992, Gorovenko 2002). Breeding birds in Iceland gray with some light gray approaching white; occasional white birds in winter, presumably migrants from Greenland (Nielsen and Pétursson 1995).

For geographic variation in size, see Measurements.

Subspecies; Related Species

No subspecies currently recognized (Am Ornithol. Union 1957, Cramp and Simmons 1980). Previously described as polytypic (see references in Cade 1960 and Cramp and Simmons 1980, Potapov and Sale 2005) with up to 3 subspecies occurring in North America (F. r. uralensis in w. Alaska, F. r. candicans in n. Canadian Arctic Islands, F. r. obsoletus in remainder of range; Am. Ornithol. Union 1931, 1957). Review of systematics (Vaurie 1961) concluded subspecific designations were inaccurate and meaningless.