The world's biggest falcon spends Arctic winters out on the sea ice
The gyrfalcon is the largest falcon alive, with some females outweighing the males by nearly double. Scientists long assumed it stuck to tundra and mountains, until 2011 revealed that many spend long winter stretches on sea ice far from land. Its plumage ranges from pure white to almost black.
Linnaeus named the bird Falco rusticolus in 1758. Falco comes from the Latin for sickle, a nod to the talons, and rusticolus means a dweller in the countryside. The first part of gyrfalcon may come from an Old High German word for vulture, reflecting its size, or from a Latin and Greek root meaning circle, after its habit of circling while searching for prey. Falconers call the male a gyrkin, and the species has been prized for hunting for centuries.
The size gap between the sexes is striking. Males measure 48 to 61 centimetres and weigh 805 to 1,350 grams; females run 51 to 65 centimetres and 1,180 to 2,100 grams, and one exceptional female from eastern Siberia reached 2,600 grams. Compared with the peregrine, the gyrfalcon is bigger, broader-winged and longer-tailed, and it sometimes competes with or even hunts its smaller cousin.
Colour varies more than in almost any other bird of prey. Breeders and biologists recognise white, silver, brown and black morphs along a continuous spectrum, with no difference between the sexes. Greenland birds are palest, Icelandic birds tend to be light, and Eurasian populations are much darker with few white individuals. Because gyrfalcons fly long distances and interbreed across regions, no living subspecies is accepted, though a genetic study found the Icelandic population distinct. A larger ice-age form lived in what is now the western United States between 125,000 and 13,000 years ago.
Unlike the peregrine's high-speed dive, the gyrfalcon usually chases prey in level flight and finishes it on the ground. Ptarmigan and waterfowl are staples, but it takes mammals more often than many falcons, especially Arctic ground squirrels and hares; both sexes can bring down adult hares of up to 4.5 kilograms. It breeds on Arctic coasts, tundra and islands across northern North America and Siberia, with some birds wandering widely in winter.
Source: Gyrfalcon
