Unusually for an owl, the snowy owl hunts mainly during the day, locating prey by both sight and sound, and hunting in all weathers. Prey may be taken from the ground, in flight, or from water, and the snowy owl will sometimes hover, or even walk along the ground in search of prey. The diet is varied and includes rodents and other mammals up to the size of hares, birds up to the size of geese, and also occasionally fish, amphibians, insects, crustaceans and sometimes carrion (2) (6) (7) (8) (11). However, the main prey, when available, is lemmings, which may be taken exclusively at times (2) (6) (8). The snowy owl is a nomadic species whose migrations are often unpredictable, and its movements are believed to relate to variable lemming abundance (6) (8).
The snowy owl is generally monogamous, and often pairs for life (2) (6). During courtship, the male performs an aerial display flight, sometimes carrying a lemming in the beak or claws (2) (6) (8), and at the start of the breeding season will defend the territory with deep hooting and with threat postures (4) (8). Breeding usually occurs between May and September, but may be abandoned in years when lemmings are scarce (2) (6) (7) (8). The nest is a shallow scrape on the ground, usually on a slightly elevated hummock or boulder, and is built by the female (2) (4) (6) (8). The nest site is often aggressively defended, the adults even striking at wolves that stray too near (4) (6). Clutch size depends on food availability, with around 3 to 5 eggs laid when food is limited, but up to 11 when conditions are good. Incubation lasts 31 to 33 days, and is performed by the female (2) (6) (7) (8) (11), whose more mottled plumage provides good camouflage against snow and rock (12). The female also cares for the young after hatching, while the male brings food to the nest (2) (6) (8) (12).
The young snowy owls may leave the nest after two weeks, but are unable to fly until about seven weeks old, and remain dependent on the adults for at least a further ten weeks (2) (6) (7) (8). The snowy owl is thought to breed from about 2 years, and may live for 10 years or more in the wild, or to at least 28 years in captivity (2) (6) (11). The irregularity of lemming abundance may mean that some individuals only breed once every three to five years (6).