This photo shows a snowy owl at the Edwin B Forsythe National Wildlife Refuge, in Galloway Township, N.J., on Wednesday Dec. 4, 2013. Birdwatchers traveled from all over to see the owl Wednesday. (AP Photo/The Press of Atlantic City, Vernon Ogrodnek) MANDATORY CREDIT A snowy owl perches on a piece of driftwood at Presque Isle State Park's Gull Point near Erie, Pa., Tuesday, Dec. 3, 2013. It's one of at least five snowy owls spotted in the Erie area in the last week. The rare birds breed in the Arctic tundra and don't visit the Erie region regularly, but they're part of a recent spate of sightings in the United States. (AP Photo/Erie Times-News, Christopher Millette) TV OUT; MAGS OUT; INTERNET OUT A snowy owl takes flight at Presque Isle State Park's Gull Point near Erie, Penn., Tuesday, Dec. 3, 2013. Birdwatchers traveled from all over to see the snowy owl at the Edwin B Forsythe National Wildlife Refuge, in Galloway Township, N.J., on Wednesday Dec. 4, 2013. ALBANY, N.Y. (AP) - Snow-white owls with luminous yellow eyes are thrilling bird-watchers as the magnificent birds set up winter residence at airports, fields and beaches far south of their normal Arctic range. Snowy owls, familiar to children as Harry Potter's pet, made a noticeable appearance in the northern half of the U.S. in 2011. Bird-watchers recently report on eBird.org snowy owl sightings in dozens of locations across the Midwest, Northeast and Mid-Atlantic states as far south as Cape Hatteras, N.C. The owls live in the Arctic, but when their population spikes or lemmings are scarce, young ones fly south. "Snowy owl populations are synchronized with their food source, lemmings," wildlife photographer Lillian Stokes, who co-authors the Stokes bird guides, said Thursday. If the lemming population crashes, the owls have to go south in search of food. A few snowy owls are seen in the U.S. every year, Stokes said. But this year is phenomenal. People believe this could be historic numbers. It's too early to say how large this year's snowy owl invasion will be, said Denver Holt, a researcher in Charlo, Mont., who has been studying the owls in Alaska for 22 years. "In 2011, it was enormous, nationwide, with sightings in 35 states," Holt said. The Cornell Lab of Ornithology website says that winter irruptions, or large numbers appearing outside their normal range, occur in snowy owls about every four years. During irruptive years, snowy owls may winter as far south as California, Texas and Florida. They're easy to see because they're big and white, are active during the day, and hang out in flat, open areas such as airports, farm fields and coastal dunes and marshes, where they hunt for mice, rabbits, waterfowl and other prey. Jessie Barrie, a scientist at the Cornell lab in Ithaca, agrees it's too early to say how this year's irruption compares to the one in 2011. "We're just at the beginning of the invasion," Barrie said. It certainly is at a level that is pretty intense and exciting for bird-watchers, though. There are multiple birds in many locations, an indication of a strong irruption. Six snowy owls have been hanging out on one dock at Braddock Bay on Lake Ontario near Rochester. Stokes said she and her husband spotted nine on the New Hampshire coast last weekend. At least 20 have been reported around New Jersey, and birders flocked to the Edwin B. Forsythe National Wildlife Refuge in that state on Wednesday to peer at a snowy owl there. Barrie said reporting by spotters in the eBird database provides researchers with valuable information that will help them better understand the movements of snowy owls and other species. Because the snowy owl, with a wingspan of 5 feet, is so impressive, its appearance in an area can inspire people to get involved in bird-watching and citizen-science projects, she said. "It's a magical bird that gets people really excited about seeing birds and engaging with the natural world," Barrie said.