In New York, there was a dust-up after news reports that officials were shooting problematic owls. That won't happen here, Brinker said. The Department of Natural Resources is working with the U.S. Department of Agriculture, which handles nuisance wildlife at BWI, on plans to trap and relocate any troublesome owls.

"Everybody's on board," he said.

Haas has spotted a snowy owl on Anne Arundel County's Gibson Island. Early Friday, he set up his scope on a beach across the river from the island, hoping to catch another glimpse. Alternating between his scope and a pair of binoculars hanging around his neck, he carefully screened the shoreline.

Spotting a snowy owl may seem easy because of its distinctive characteristics, but it's easy to get tricked. When your eyes are peeled for big white birds, things such as white plastic bags at a distance can get your hopes up.

Wierenga, who lives in Arnold and joined Haas on Friday morning, admitted to being momentarily fooled by a sun-bleached plastic owl decoy on a pier on the Magothy River. But when you see a real one, he said, you get a rush of adrenaline.

"It's a lot of frustration followed by bombs-away elation," Haas said.

Haas and Wierenga set out Friday on the Magothy, but in Harford County, birders and photographers have been swooning over a snowy owl at a farm in Level.

Hopkins Farm, in a rural corner north of Havre de Grace, has attracted a stream of curious onlookers and weathered bird-watchers since Sunday, when a snowy owl was spotted during a snowstorm by a Harford Bird Club member.

Richard Donham has been bird-watching since he was a child, but said he had not seen a snowy owl in 20 years.

"It's a beautiful bird," said the Oxford, Pa., resident as he kept his camera trained on the owl on a hilltop.

Sharon Stafford came with her husband from Hanover in Anne Arundel to see the owl. "It's a lovely bird," she said. "It's beautiful when it flies over the snow."

Snowy owls — like all wildlife — should not be fed or bothered by humans. Bird-watchers also should be careful not to trespass or cause problems for parks or landowners, Brinker said.

"Go out and enjoy them," he said. "This is the kind of thing, for the average person who doesn't spend all their time bird watching, it's the best opportunity to see a snowy owl."

Baltimore Sun Media Group reporter Bryna Zumer contributed to this article.