Distinguishing Characteristics

Adult Gyrfalcon, gray variant; Idaho, January

First-winter Gyrfalcon (gray variant); Oregon, February

Juvenile Gyrfalcon, gray variant.

Large falcon (length: males 48–61 cm, females 51–64 cm). No seasonal variation in plumage. Sexes best distinguished by size (see Measurements). Immatures exhibit vertical streaking and are more heavily marked on ventral surface than adults. Cere, eye ring, and feet of immature birds are light blue-gray. Adults’ ventral surface is generally horizontally barred posteriorly and spotted anteriorly; bare parts yellow.

Dark eye and tomial tooth distinguish North American falcons from other raptors. White Gyrfalcon is unmistakable; no other falcon is white. Most dark Gyrfalcons distinguished from Peregrine Falcon by crown and/or nape heavily streaked with cream, and absence of pronounced facial stripe and cap. Birds with gray plumage are most easily misidentified, but differ in plumage from Peregrines by having a two-tone underwing visible in flight and absence of a bold helmet. All Gyrfalcons distinguished from Prairie Falcon (Falco mexicanus) by absence of dark contrasting axillaries. Also distinguished from both Peregrine and Prairie falcons by larger size, proportionately longer tail and shorter, more broadly based wing with rounder tip. Primary formula usually 9 > 8 > 10 > 7, compared to Peregrine Falcon (9 > 10 > 8 > 7) or Prairie Falcon (9 ≥ 8 > 10 ≥ 7). These characters give the Gyrfalcon an accipitrine appearance in flight, and when flying low it can be confused with the Goshawk (Accipiter gentilis). Wing beat slower, deeper and more powerful than other falcons, but flight is faster and more sustained.