The gyrfalcon is a bird of prey, the largest falcon in the world. Its plumage varies with location, with birds being colored from all-white to dark brown. These color variations are called morphs and can be "white", "silver", "brown", and "black". 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 morph has a strongly black-spotted underside, rather than finely barred as in the peregrine. White form gyrfalcons are the only predominantly white falcons. Silver gyrfalcons resemble a light grey lanner falcon of larger size. Juveniles are darker and browner than adults. Like in other falcons, the female is much larger than the male.
Gyrfalcons occur on Arctic coasts, and the islands of northern North America, Europe, and Asia. They are mainly resident there also, but some gyrfalcons disperse more widely after the breeding season, or in winter. These birds inhabit tundra, taiga, and mountains with rocky outcrops and cliffs. They are also known to spend considerable periods during the winter on sea ice far from land.
Gyrfalcons are generally solitary birds and interact with their mates only during the breeding season. They are diurnal and hunt by fast flight low over the ground. They usually hunt in a horizontal pursuit, rather than with the peregrine's speedy stoop from a height. Most prey is killed on the ground, whether they are captured there, or if the victim is a flying bird, forced to the ground. Gyrfalcons are generally silent birds but near the nest, they produce loud “kiak kiak kiak” and “gik-gik”; when excited they will make a “giiiii” call.
Gyrfalcons are strictly carnivores. Typical prey includes the ptarmigan and waterfowl, which they may take in flight; they also take fish and mammals. Avian prey can include gulls, corvids, smaller passerines, waders, and other raptors. Mammalian prey often includes lemmings, voles, ground squirrels, hares and rarely also bats.
Gyrfalcons are monogamous and pairs mate for life. During the breeding season pairs perform several courtship displays including aerial display and displays at nest-site. Gyrfalcons nest mainly on cliff faces. Breeding pairs do not build their own nests, and often use a bare cliff ledge or the abandoned nest of other birds, such as golden eagles and common ravens. The clutch can range from 1 to 5 eggs but is usually 2 to 4. The incubation period averages 35 days, with the chicks hatching at a weight of around 52 g (1.8 oz). The nestlings are brooded usually for 10 to 15 days and leave the nest at 7 to 8 weeks. At 3 to 4 months of age, the immature gyrfalcons become independent of their parents, though they may associate with their siblings through the following winter. They become reproductively mature and are ready to breed at 2-3 years of age.
The most significant current threat to these birds is climate change. In the early 2000s, it was observed that as climate change began to temper the Arctic summers, peregrine falcons were expanding their range north, and competing with gyrfalcons. Although it is specially adapted for high-Arctic life, and larger than the peregrine, the gyrfalcon is less aggressive and more conflict-averse, and so is unable to compete with peregrines, which regularly attack and overwhelm the gyrs. There is a fear that gyrs will become extinct in their former range within the next ten to fifteen years.
According to the IUCN Red List, the total gyrfalcon population size is around 20,000-49,999 mature individuals. The European population is estimated at 1,100-1,900 pairs, which equates to 2,200-3,900 mature individuals. According to the All About Birds resource, the total breeding population size of the species is 70,000 individuals. Overall, currently, gyrfalcons are classified as Least Concern (LC) on the IUCN Red List and its numbers today stable.