Snowy owls are more diurnal then most owls.It makes sense that they would have to be active during daytime hours during the nesting season, which runs from may through September. During the summer daylight can stretch to over 20 hours per day. Birds that stay on the nesting territory during the winter would have to switch to nocturnal hunting because of lack of daylight during the winter. The primary prey of the snowy owl are lemmings. They will also eat other small mammals as well as ptarmigan and water fowl.
Occasionally there are mass eruptions of snowy owls down into Europe, Asia, or the United States. These typically occur because of a lack of food in their tundra territories. this lack of food can be caused by a bad year for the prey species, such as a decline in the lemming population due to disease, or it can be caused by a particularly good breeding season. as a ground nesting bird snowy owls can lay up to 11 eggs in a clutch. most years a snowy pair can not support that many chicks and some do not make it. On a good year where there is plenty of prey during the breeding season more chicks survive and when it comes time for them to go out on their own in the winter many head south to find food. This past winter was a huge snowy eruption in the US. Snowies were seen all the way down in Florida. Most of the snowies that I spotted were immature birds which suggests that it was a good breeding year for snowies. Unfortunately many of the snowies that came south will never make it back.