Biography: The heaviest of all North American owls, snowy owls are well adapted for life on the Arctic tundra. Very thick plumage and heavily feathered legs and feet insulate snowy owls against extremely cold temperatures. These striking owls hunt by night or day, depending on seasonal changes in Arctic daylight. Although snowy owls prey upon hares, ground squirrels and birds, small tundra rodents called lemmings are their most important food. Snowy owl breeding is closely tied to cyclic changes in lemming numbers that peak and crash at roughly four-year intervals. When lemmings are plentiful, the owls can lay up to twelve or more eggs in a clutch. Snowy owls lay fewer eggs, or none at all, if lemmings are scarce. Better camouflaged than males, the more heavily spotted females incubate eggs and brood young, while males provide the food. Nests are shallow depressions scraped in the ground, usually located on hillocks for a commanding view.
Snowy owls are circumpolar, inhabiting the Arctic regions of North America and Eurasia. Winter migration is irregular. Although some snowy owls winter on the tundra, others will migrate to the open plains of southern Canada and the northern United States. Lemming population crashes and severe weather may force snowy owls to migrate as far south as Pennsylvania or beyond, in search of winter prey.