The Gyrfalcon ( Falco rusticolus ) is the largest falcon globally, a powerful bird that commands the Arctic skies. This formidable raptor inhabits some of the planet’s most extreme environments, thriving across the circumpolar regions of North America, Europe, and Asia. It reigns as an apex predator in its northern home.
Appearance and Adaptations
Males typically measure 48 to 61 centimeters (19 to 24 inches) in length and weigh 805 to 1,350 grams (1.75 to 3 pounds). Females are noticeably larger, ranging from 48 to 64 centimeters (19 to 25 inches) and weighing 1,260 to 2,100 grams (2.1 to 4.6 pounds), with a wingspan of 110 to 135 centimeters (43 to 53 inches). This size difference between sexes is a common trait among raptors.
Gyrfalcons display various plumage colors, known as morphs, which are not distinct subspecies but rather variations within the species across their range. These morphs include white, silver/grey, and dark/blackish-brown variants. White morphs are found in regions such as northern Greenland, appearing almost pure white with black spotting, offering superb camouflage in snowy landscapes.
Grey morphs, the most common in North America, feature gray upperparts with lighter feather edging and gray barring on their white underparts, blending well with rocky or partially snow-covered terrain. Dark morphs exhibit blackish-brown upperparts, a dark hood, and mottled underparts, providing concealment in darker, exposed rock environments. All morphs have dark brown eyes, and their legs and feet are pale yellowish-grey in adults.
Beyond camouflage, Gyrfalcons possess specialized physical adaptations for surviving Arctic cold. Their legs and feet are densely feathered down to their toes, providing insulation against freezing temperatures. This feathering minimizes heat loss from exposed skin, allowing them to withstand the harsh conditions of their northern habitat.
Hunting and Diet
Gyrfalcons are agile predators, employing a hunting style distinct from other falcons. Unlike the Peregrine Falcon’s high-altitude stoop, Gyrfalcons often pursue prey in a rapid, level flight. They exhibit powerful wing beats and periods of gliding, resembling a Goshawk’s flight, allowing them to chase down even fast-flying waterfowl.
Their primary diet consists of birds, with ptarmigan species (Willow and Rock Ptarmigan) forming 50-90% of their prey biomass, particularly during the breeding season. The distribution of Gyrfalcons is closely linked to ptarmigan availability. When ptarmigan numbers are low, they supplement their diet with other birds, including waterfowl like geese and ducks, seabirds, waders, and other raptors.
Gyrfalcons also hunt mammals, such as Arctic hares, ground squirrels, lemmings, voles, and rabbits. They are versatile hunters, capable of taking prey both in the air and on the ground. During the breeding season, a family of Gyrfalcons requires 0.9 to 1.4 kilograms (2-3 pounds) of food per day, with females caching leftovers near the nest for later consumption.
Life Cycle and Conservation Status
Gyrfalcons begin their breeding season between March and July, though courtship and pair-bonding can start in January or February, with eggs laid by late April. These solitary nesters do not construct their own nests. Instead, they utilize scrapes or depressions on cliff ledges, often protected by overhangs, or occupy abandoned stick nests built by other large birds like ravens or Golden Eagles. Males defend the nesting territory, and both sexes visit potential sites before breeding.
Clutch size ranges from 2 to 7 eggs, with an average of 4 eggs. The female primarily incubates the eggs for 34 to 36 days, with some assistance from the male. After hatching, the young falcons are covered in thick down and can thermoregulate themselves after 10 days, allowing the female to join the male in hunting duties to support the growing family. The young fledge, or take their first flight, six to seven weeks after hatching and are ready to reproduce when they are two to three years old.
Globally, the Gyrfalcon is listed as a species of “Least Concern” by the IUCN. Population estimates are below 50,000 birds, with stable long-term population levels in North America. Despite this, the species faces long-term threats, with climate change being a concern. A warming Arctic is transforming their habitat and can impact prey populations, particularly ptarmigan, a major food source. Historically, Gyrfalcons have been highly prized in falconry, with their use once reserved for royalty in the Middle Ages.