The gyrfalcon is the largest falcon in the world, and gyrfalcons live in the far north, in the Arctic, where they are top predators. No living subspecies of the gyrfalcon are currently accepted. Gyrfalcons are one of four falcon species that breed in Alaska, and the scientific name Falco rusticolus means a countryside-dwelling falcon.

In winter some gyrfalcons move south, and some stay in their territories. Scientists discovered as recently as 2011 that some gyrfalcons spend a lot of the winter out on the ocean, far from any land. An adult male gyrfalcon tracked by satellite travelled 3,137 kilometers in 38 days (83 kilometers per day) from northern Ellesmere Island to southern Greenland.

Breeding home ranges of seven satellite-tracked adult female gyrfalcons in Greenland varied from 140 to 1,197 square kilometers. Gyrfalcon territories on the Yukon-Kuskokwim Delta were 3.70 to 5.49 kilometers from their nearest neighbors on average in three study areas. As of January 2011, researchers knew of 79 gyrfalcon nesting territories in a region of 130,000 square kilometers there. On the Seward Peninsula, about 70 to 80 pairs of gyrfalcons nest, about one-tenth of Alaska's total, as reported in 2020.

Gyrfalcons eat mostly other birds, and ptarmigan are the gyrfalcon's main food. On the Yukon-Kuskokwim Delta, ptarmigan made up 58 percent of the prey items at 15 nest sites in the Askinuk Mountains. Prey numbers strongly influence the breeding success and density of gyrfalcons. Cameras at gyrfalcon nests on the Seward Peninsula showed that gyrfalcons rely heavily on ptarmigan but also change their diet when ptarmigan numbers drop.

A gyrfalcon hunts by scanning from a high rock perch or while flying, and it uses keen eyesight to spot potential prey. It often hunts by flying fast and low over the ground, usually in a level chase rather than a steep dive, and it may chase its prey over long distances.

Alaska biologists fly slowly past mapped nest cliffs by helicopter and check whether raptors are using them, without landing. Alaska biologists had two observers each survey historic gyrfalcon nest sites in three reference areas, to estimate how well different observers see nests. Biologists on the Seward Peninsula band gyrfalcon chicks when they are about 25 days old so the birds can be identified in the future, and in July 2012 they collected 854 molted gyrfalcon feathers from 58 nest cliffs for genetic analysis.

The gyrfalcon has been less affected by DDT and other pesticides than the peregrine falcon, and it seems to have escaped the severe declines in birds of prey that DDT caused in the last half of the 20th century. Audubon's field guide, read in 2026, says North American gyrfalcon populations are probably stable, though the bird has declined in parts of arctic Europe. As of 2026, the IUCN Red List lists the gyrfalcon as Least Concern.

The mean size of 100 clutches of gyrfalcon eggs on the Yukon-Kuskokwim Delta was 3.43 eggs, and the eggs take about five weeks to hatch. For the first one to three weeks, the male does all or most of the hunting while the female broods the young. Gyrfalcon chicks hatch at a weight of around 52 grams.

Young gyrfalcons begin short practice flights at about five weeks old and spend the next eight weeks or more honing their flying. At 3 to 4 months old, young gyrfalcons become independent of their parents. Juvenile gyrfalcons tagged with satellite transmitters in the Swedish mountains had a median pre-dispersal home range of 266 square kilometers, which varied greatly. Tracked young gyrfalcons in Sweden stayed near the nest until late August.

Words to know

• subspecies: local kinds
• transmitters: tracking tags
• pesticides: farm poisons
• raptors: birds of prey
• ptarmigan: a bird