Snowy owls are hard to count because they are irruptive and nomadic and breed in remote Arctic tundra, and tracking showed snowy owls to be among the great nomads of birds, ranging thousands of miles across the Arctic. One tracked snowy owl moved 881 miles (1,418 km) across an area of 1,784 square miles (4,621 sq. km), and a snowy owl breeding in central Canada one year may be in Greenland the next. Snowy owls do not show fidelity to a particular breeding site, since they do not return to the same place each year. Some winters, many more snowy owls than usual move south out of the Arctic, and Project SNOWstorm found that a big move south is a baby boom: young owls come south after summers of plentiful lemmings.

Birdwatchers help count snowy owls by reporting sightings through eBird, and Project SNOWstorm tags snowy owls with a backpack harness of low-friction ribbon that goes over the bird's wings. Older satellite tracking logged a single location a day at best, but the cellular tags used by Project SNOWstorm can store up to 100,000 locations. As of August 2024, the project was using, in 2024, satellite transmitters that weigh just 17 grams, instead of the 45-gram GPS/GSM units it normally uses, and it had put satellite transmitters on 10 young owls from six nests on Bylot Island. On Bylot Island, researchers also fitted females with satellite transmitters and tracked their movements in real time for up to 3 years.

As recently as 2004, scientists thought the global snowy owl population might be as high as 290,000. As of November 2026, a 2024 global review put the world population at 14,000 to 28,000 breeding-age adults, and the global assessment drew on long-term breeding data, genetic studies and satellite-GPS tracking from several Arctic monitoring sites. As of February 2015, snowy owl population figures were still, in one scientist's words, just educated guesses.

As of November 2026, the IUCN Red List lists the snowy owl as Vulnerable, and the IUCN moved the snowy owl from Least Concern to Vulnerable in 2017. As of November 2026, snowy owl populations have decreased by more than 30% in the past three generations, so the Vulnerable category was kept. As of November 2026, Canada's COSEWIC re-examined the snowy owl and designated it Threatened in May 2025, and it estimated 13,000 to 16,000 mature snowy owls in Canada, where 90 to 95% of North American snowy owls breed.

The snowy owl is the heaviest owl in North America, and one of the largest in the world. A snowy owl measures 20 to 27 inches from the tip of its bill to the tip of its tail, with a wingspan of 4.5 to 5 feet, and adult snowy owls weigh about 3.5 to 6.5 pounds. The mean body mass of adult snowy owls, from a large set of records, was 1636 g for males (995 birds) and 2109 g for females (1189 birds), and female snowy owls are larger and heavier than males. Feathers cover a snowy owl's legs and feet, and all four toes are covered with long feathers that reach the ground when it perches.

When hunting alone, snowy owls appear to prefer evening into darkness and early mornings, and winter observations with night-vision equipment show snowy owls have an active nocturnal hunting period, though it is less studied. Snowy owls hunt at any time of day, except in severe weather. After spotting prey, a snowy owl uses at least five hunting techniques: chase, drop, glide, run or slip. Each snowy owl must catch the equivalent of 7 to 12 mice a day to meet its food needs, and a snowy owl may eat about 1,600 lemmings in a year.

Words to know

• nomadic: always wandering
• nocturnal: active at night
• harness: body strap
• transmitters: signal senders