Snowy owls, denizens of the high Arctic with more than 4-foot wingspans, are showing up in large numbers across Minnesota and other Great Lakes states this winter. Many also have been seen along the New England coast.

Such an unpredictable invasion is called an "irruption" by birdwatchers.

As of Wednesday, Dec. 13, an estimated 173 snowy owls had been observed in 57 of Wisconsin's 72 counties, said Ryan Brady, a conservation biologist with the Wisconsin Department of Natural Resources in Ashland.

That compares with 13 by the same time in 2016-17, 102 in 2015-16, 161 in 2014-15 and 91 in 2013-14, Brady said.

Nine rescued snowy owls have been admitted to Wildwoods, a wildlife rehabilitation facility in Duluth, in late November and early December. "That's far more snowy owls than we've ever had," said Farzad Farr, Wildwoods director.

Only two survived, he said, and both are now recovering at the Raptor Center in St. Paul. One of those, rescued from the base of a chimney at Alakef Coffee Roasters in Duluth, is expected to be released soon, Farr said.

Semi-regular occurrence

Snowy owl irruptions typically occur about every four years, Brady said, but this year's invasion marks three of the past five years with significant irruptions.

Wisconsin is the only state that keeps a semi-official count of snowy owls during an irruption year, but many have been spotted in Minnesota as well according to Ebird News, a service of the Cornell Laboratory of Ornithology.

"In October and November, snowy owls started appearing," said Duluth birder Laura Erickson, host of the "For the Birds" radio program.

And, no, they're not starving.

"Most of the owls we get, even in an irruption, are healthy. They're just out of their range," Erickson said.

Snowy owl irruptions are not fully understood, but they typically occur for one of two reasons, Erickson said. The snowy owl population in the Arctic is tied closely to the population of lemmings, one of their main prey sources. In years when the lemming population crashes, many snowies move south looking for food.

In years when the lemming population is high, female snowy owls produce more eggs and hatch more young. Snowies in the Arctic are territorial, and young birds can't compete effectively for food. So, in years of those big hatches, many young birds move south to find their prey.

In this year's irruption, about 90 percent of the snowies appear to be juveniles, the DNR's Brady said.

"This tells you they had really high reproductive success in the Arctic," he said. "They raised lots of babies. Those babies have to go somewhere, and they end up down here."

They'll be here for the winter, then return north in the spring.

Where to see them

Because snowy owls are native to the tundra, they tend to prefer open spaces even when they come south. They're typically seen near airports, the Duluth-Superior harbor or open areas such as fields and bogs, Erickson said. They perch on high places like utility poles, light posts or piles of snow.

Unaccustomed to their new surroundings, immature snowy owls "land in weird places," Brady said.

"We're seeing a fair number of pictures of them sitting on people's cars," he said.

Adult snowy owls are more skittish, he said.

Erickson said snowy owls can be stressed by too much human activity nearby. If you see one, she said, it's best to remain in your car and take photos through the window rather than to get out. Some birders don't readily share locations of the owls they've located to prevent crowds from gathering. And there's an ongoing debate among photographers about the ethics of using bait - such as a mouse - in order to draw the owls closer.

The snowy owl

Description: Mostly white, large, round-headed, with small yellow eyes; male's plumage often broken with dark bars or spots.

Length: 23 inches

Wingspan: 52-60 inches

Weight: 4 pounds

Breeding territory: Open tundra

Source: "National Geographic Complete Birds of North America" and David Sibley's "Field Guide to Birds"