Closest to F. cherrug; genetic data indicate that these two, along with F. biarmicus and F. jugger, form a group of closely related species#R. Has hybridized with F. peregrinus#R. Taxonomy complicated. Usually considered monotypic, but highly polymorphic, and this is partially responsible for considerable discussion as to species’ valid name, with F. rusticolus in general usage (selected by First Reviser) and recently defended against F. gyrfalco, which is frequently used in Russian literature#R; others maintain that F. rusticolus is an invalid name for F. peregrinus, and that either F. gyrfalco or even F. canadensis should be used for present species#R. Sometimes regarded as polytypic, normally with four races (rarely, up to seven#R), based mainly on colour frequencies: rusticolus (Europe); obsoletus (Asia, parts of North America); candicans (high Arctic of North America, Greenland); and islandus (Iceland), the most isolated, uniform and distinctive of these forms, which would probably be most valid race. Described form altaicus of F. cherrug has been listed as race of present species (see F. cherrug). Monotypic.
Circumpolar, occupying Arctic regions of Eurasia, North America, Greenland and Iceland; some birds move farther S for winter.
48–60 cm; male 769–1450 g, female 1130–2150#R g; wingspan 105–135 cm#R. The largest Falco, with larger head, deeper chest, relatively short but broad outer wings and longer tail than other large falcons#R. Extreme polymorphism in coloration, with three main colours, white, grey and blackish brown. Streaked or barred on underparts; white birds with some dark markings on upperparts and underparts. Legs and feet yellow, but extremely long and dense thigh feathers often completely cover them#R. Female larger (7–25%) and heavier (8–160%)#R, sometimes darker. Juvenile generally darker, browner and more heavily streaked below; legs and feet pale grey. Other than white morph birds, F. rusticolus is most similar to F. cherrug, but latter almost wholly allopatric. Some female F. peregrinus of northernmost races appear almost as bulky, but shorter tailed, narrower and more pointed winged, with uniformly dark-barred underwings#R. In Nearctic, confusion also possible in winter with F. mexicanus, but latter is smaller and paler, and has different head and underwing patterns#R. The three main colour morphs vary and grade into one another, sometimes along clines, or at any rate with colour morph ratios differing regionally: birds in high Arctic of Greenland usually white; in Labrador, preponderance is dark brown or even blackish; in Iceland, normally various shades of grey; clinal W to E across Russia and Siberia, with 90% grey drifting into 47% white; also slight variation in size, with larger birds in N of range.
Food and feeding
Mainly birds and to lesser extent#R mammals up to size of hares#R. Frequently a major reliance on ptarmigan/grouse (Lagopus) and ground squirrels (Spermophilus) for breeding, but regularly takes birds as small as finches#R; in coastal areas, seabirds may be major food; lemmings (Lemmus, Dicrostonyx) can be mainstay in some areas depending on season. During winter food may be more restricted, where species resident, but more varied for those migrating S, where prey as large as Sage Grouse (Centrocercus) is killed#R. Most hunting by fast flight low over ground, often rising to make rapid stoop; sometimes forages by flying along high up (150–300 m above ground)#R, or perches to scan. Prey taken on ground or water more often than in air, but sometimes after hot pursuit.
Mar–Jul, but territories may be held all winter so breeding essentially starts Jan–Feb. Solitary. Eggs laid in unlined scrape or depression in cliff ledge, disused stick nest of another species on cliff (usually either Common Raven Corvus corax, Golden Eagle Aquila chrysaetos or Rough-legged Buzzard Buteo lagopus)#R, or occasionally stick nest in tree or on man-made structure, e.g. gold dredger or oil pipeline. Usually 3–4 pale buffish or yellowish-white eggs finely spotted red or reddish brown#R (2–7 in years of food extremes) laid at c. 3-day intervals, size 58·9 mm × 45·9 mm#R; incubation 28–36 days, begins with first egg, usually by female alone#R; chicks have creamy-white first down, second longer, coarser and greyish white#R; fledging 46–53 days, with young fed by female, provisioned by male#R. Nest success varies dramatically in response to cyclical food sources: 1·3–4·0 young per successful nest, but generally c. 2·5–3·1 over many years; occupation of c. 31–88% of total territories available; 38–73% of occupied territories produce young. In CW Greenland, where multiple colour variants present, white males fathered signiﬁcantly earlier clutches than grey males (no signiﬁcant association between female colour and laying date), white adults (both sexes) produced signiﬁcantly more offspring than did grey ones, and silver adults (both sexes) produced intermediate number of young; also, grey females paired with grey males nested signiﬁcantly later in season and produced fewer young than females with white mates, whereas no difference in laying date or offspring number between white males paired with white females and those paired with grey females; further, number of offspring produced at each nest-site was inversely correlated with distance to nest of nearest neighbour, grey males nesting closer to other nests than did white and silver variants#R. Although territory fidelty is high, in Alaska birds frequently change nest-site (with mean distance between alternate sites 750 m), and mean tenure of a territory is 2·8 years#R. Home range at this season much smaller than in winter (see Movements), between 140 and 1197 km2#R. Usually first breeds in second or third year; in Iceland, some breed by end of first year. Young have been recorded breeding up to c. 250 km from their natal area#R. Oldest wild birds c. 13 years old.
Many adults sedentary, especially in Iceland and Scandinavia#R; juveniles generally more dispersive and move farthest S. Patterns complicated by cyclical food availability, which may cause irruptive movements, but some very clear movements, e.g. white morph birds from Greenland to Iceland. Some move from North America to Siberia (see Family Text). At least some birds recently confirmed to#R winter around edge of sea ice or near open water (polynyas), presumably feeding on seabirds and resting on icebergs#R. Distances moved in winter exceptionally 3400 km (from Alaska to Arctic Russia)#R, and 4234 km from NW to S Greenland#R. Winter home range huge, e.g. 26,810–63,647 km2 in E Greenland, and one young female moved 4548 km over c. 200-day period#R. Most birds winter N of 52° N and some in low Arctic may scarcely move from their breeding sites#R; in North America has reached S to 35° N (Oklahoma)#R, in Eurasia c. 46° N (Iberia and Italy)#R. Occasionally recorded in summer as far S as British Isles#R.
Status and conservation
Not globally threatened (Least Concern). CITES I. Widespread; rare in some regions, locally common in others but status confounded by cyclical nature of numbers. Densities vary regionally with rather wide ranging estimates of total population from c. 5000–7000 to 15,000–17,000 pairs. Some estimates are: Alaska (USA) 375–635 pairs; Yukon Territory (Canada) 750 pairs; Northwest Territories (Canada) 1300 pairs; Greenland c. 750 pairs; Iceland c. 350 pairs; Scandinavia c. 120–150 pairs; 50 pairs in European Russia, with only 10–15 pairs over area of 14,000 km2 in extreme NE; no survey results for Siberia. Not affected by organochlorines during 1960s and 1970s, as were other Falco. Surveys of a locality in C Canadian Arctic in 1982–91 revealed stable population there#R. Recent mortality at hands of trappers in Siberia (e.g. Yakutsk, Indigirka R) suggests that c. 1000–2000 killed annually throughout Arctic Russia. Highly prized in falconry, with unknown number taken annually; probably not enough to affect breeding population. Now bred in captivity for falconry and research in North America, Europe and Russia.
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