Some gyrfalcons disperse more widely after the breeding season or in winter, and individual vagrancy can take birds for long distances.

Typical prey includes the ptarmigan and waterfowl, which it may attack in flight; and it also hunts fish and small mammals.

The gyrfalcon was formally described by Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae under its current binomial name Falco rusticolus.

[5] The genus name is the Late Latin term for a falcon, Falco, from falx a sickle, referencing the talons of the bird.

The brown form of the gyrfalcon is distinguished from the peregrine by the cream streaking on the nape and crown and by the absence of a well-defined malar stripe and cap.

The black color seems to be sex-linked and to occur mostly in females; it proved difficult for breeders to get males darker than the dark side of slate grey.

In this group, ample evidence indicates hybridisation and incomplete lineage sorting, which confounds analyses of DNA sequence data to a massive extent.

The radiation of the entire living diversity of hierofalcons took place around the Eemian Stage at the start of the Late Pleistocene.

It represents lineages that expanded into the Holarctic and adapted to local conditions; this is in contrast to less northerly populations of northeastern Africa (where the radiation probably originated) that evolved into the saker falcon.

Instead, this research suggests that gyrfalcons may have evolved from eastern saker falcons, explaining their close genetic relationship.

For instance, a mating of a pair of captive gyrfalcons is documented to have produced a clutch of four young: one white, one silver, one brown, and one black.

This dispersal bias is in agreement with the distribution of plumage colour variants with white gyrfalcons in much higher proportion in north Greenland.

[19] Although further work is required to determine the ecological factors contributing to these distributions relative to plumage differences, a study using demographic data suggested that plumage color distribution in Greenland may be influenced by nesting chronology with white individuals and pairs laying eggs earlier in the breeding season and producing more offspring.

Fossils found in Little Box Elder Cave (Converse County, Wyoming), Dark Canyon Cave (Eddy County, New Mexico), and McKittrick, California were initially described as Falco swarthi ("Swarth falcon" or more properly "Swarth's gyrfalcon") on account of their distinct size.

The gyrfalcon was originally thought to be a bird of tundra and mountains only; however, in June 2011, it was revealed to spend considerable periods during the winter on sea ice far from land.

[27][28][29][30][31][32] Seabirds such as auks, gulls and seaducks may predominate in coastal areas, and waders and ducks such as mallards (Anas platyrhynchos) on wetlands.

[27][36][37][38] Other mammalian prey can include mice, water voles, muskrats, stoats, minks, Arctic fox pups, and rarely also bats.

[32] In the early 2000s, it was observed that as possible climate change began to temper the Arctic summers, peregrine falcons were expanding their range north to parts of Greenland, and competing with gyrfalcons.

Humans, whether accidentally (automobile collisions or poisoning of carrion to kill mammalian scavengers) or intentionally (through hunting), are the leading cause of death for gyrfalcons.

[45] In the 12th century AD China, swan-hunting with gyrfalcons (海東青 hǎidōngqīng in Chinese) obtained from the Jurchen tribes became fashionable among the Khitan nobility.