Snowy owls, normally residents of the arctic, are beginning to make their homes in greater numbers throughout the United States and Canada. During summer months, these birds live above the Arctic Circle, hunting prey in the constant sunlight.

Data on snowy owl populations was gathered by amateurs, participating in the Great Backyard Bird Count. This event, sponsored in part by Cornell University, began on 14 February and lasted three days. Over 2,500 members of the species were spotted by participants in 25 states and seven Canadian provinces. These were mostly northern states, including New England, New York and the northern plains.

Snowy owls grow to over two feet in length, and can weigh as much as six-and-a-half pounds. This makes them the second-heaviest bird in North America. The also have striking yellow eyes, which look much like those of cats.

Ornithologists believe the change in snowy owl habitat may be due to a population increase, combined with declining numbers of lemmings in arctic regions. These small rodents are a favorite food of the birds. When winter comes to the northern climates, lemmings are better able to burrow in deeper snow. Researchers believe snowy owls then fly down the Atlantic coast in search of food.

Lemmings populations are starting to decline in Greenland and Scandinavia, as polar temperatures rise. This could help account for rising populations of the birds in North America. Snowy owls hunt a wide variety of animals.

"They will eat pretty much anything they can jam down their throats - ducks, gulls, geese, muskrats, great blue heron. They're a very big, very strong, very capable predator. On the Delaware coast, they were seen feeding on a dolphin carcass. That's a new behavior we're documenting this year," Scott Weidensaul, co-director of Project Snowstorm, told the Washington Post.

For birdwatchers in the northern half of the country, especially in the northeast, this can be a chance to see a species of bird they have never observed. Most ornithologists believe the movement of snowy owls to the U.S. does not pose an immediate danger to the species, due to their diverse diet.

This is the 17th year for the annual bird watch. The event is open to anyone in the world, and sightings are reported online, before being analyzed by ornithologists.

"People who care about birds can change the world. Technology has made it possible for people everywhere to unite around a shared love of birds and a commitment to protecting them," Gary Langham, Audubon chief scientist, said.