Gyrfalcon is the largest, most powerful, rarest N.A. falcon, and likely the most sought after raptor by birders. It is a denizen of the Arctic, nesting on cliffs above vast expanses where they hunt large birds (e.g., ptarmigan, waterfowl), and sometimes medium-sized mammals (e.g., Arctic Hare). Females are considerably larger than males and can take larger prey. Gyrfalcons hunt using 'surprise and flush' tactics, cruising low over the terrain to scare up birds. When prey is flushed, Gyrfalcons can accelerate in an instant and chase down even the fastest waterfowl. Gyrfalcons will stoop from high altitudes as well, and may do so in pairs on the breeding grounds. They often knock prey from the sky and then retrieve it on the ground. Gyrfalcons are quiet birds but make an agitated "Kak-Kak-Kak-Kak" call similar to Peregrines but slightly lower pitched and slower.
During winter, they occur in the Lower 48 but only scarcely. they perch on rock outcrops, hilltops, and man-made structures, especially utility poles in open areas such as varied grasslands and agricultural areas. Gyrfalcons are known to inhabit parts of the Pacific Northwest, especially the Skagit and Samish Flats, WA. They are also regular winter visitors in open areas of MT, ID, and around Sault St. Marie, MI. One of the most reliable winter sites is the grasslands around Pierre, South Dakota. One or two are usually reported in New England each winter. They are much less common farther south. Many adults remain in the Arctic year-round, and some even spend the winter on pack ice where sea duck concentrations occur.
Hybrid Gyrfalcons are not known to occur in the wild, but are common in falconry. Hybrids can appear nearly identical to one species or look like a combination of both species. Some falconry birds escape into the wild, but often have jesses (leather anklets) or rings on their legs.
Perched, Gyrfalcon has hulking chest and shoulders, tapering towards the belly, with small-headed appearance. Tail is very long, and wing tips fall short of tail tip.
In flight, wings and tail of Gyrfalcon are slightly broader than those of Peregrine and Prairie falcon, and wing tips more bluntly pointed. Also, heavy chested and long tailed.
Wing beats are shallower, stiffer, less 'whip-like' than Peregrine, more like Prairie Falcon but more labored.
Soars in wide circles on flattish wings, sometimes with slight dihedral.
Very steady flier in all conditions.
Gyrfalcon is lumped into three categories: white, gray, or dark-morph, but there is a complete cline from white to dark, so some birds are difficult to classify. Most Gyrfalcons are gray-morph, with white and dark-morph uncommon. Male and female identical in plumage. Juvenile has bluish cere, eye-ring, and feet/legs, that changes yellow after one to several years. Eyes are dark brown.
White-morph adult is beautiful, snow-white below and lightly spotted with black. The very tips of the primaries are black. The upperparts are white with dark barring on the upperwing coverts. Juvenile similar to adult, but more heavily marked above and faintly black-streaked below. The tail pattern on all Gyrfalcons is indistinct with faint bands, though white-morph can be wholly white tailed or distinctly banded black and white.
Gray-morph adult similar to Peregrine Falcon but paler overall, evenly spotted underneath, and lacks the white-chested look. Head of adult acks the distinct black 'hood' and bold black moustache. Juvenile has dark streaking underneath that is less heavily marked than most Peregrines, but often more solidly dark head, and brown upperside with pale-fringed coverts (paler overall than juvenile Peregrine). Almost all juvenile gray Gyrfalcons show streaked undertail coverts compared to barred on Peregrine, and flight feathers of are less boldly marked.
Dark-morph adult is dark slate-gray on top with faint barring and blackish head. Adult has faint pale barring to underside, but appears solidly dark with no distinct field marks. Juvenile is either solidly dark or with faint pale streaks underneath.
Gyrfalcon migration is poorly understood, but birds are seen south of their breeding range mainly from November to April.
Gunsight Mt., AK is the most likely places to see Gyrfalcon on (spring) migration.
In the lower 48, the Eastern Rocky Mountain foothills of Montana, the Canadian shorelines of the Great Lakes, and western shore of Lake Superior are the best spots to see a Gyrfalcon during migration.
(Map from Cornell Lab of Ornithology's All About Birds. For dynamic distribution maps, visit the eBird website.)