When five of the birds took up residency at Smithville Lake, near Kansas City, Mo., it created an “owl jam,” Mr. Robbins said. Thousands of people have driven there to see them, he said, and hundreds of owl seekers have shown up at Clinton Lake near Lawrence, Kan.

Unlike many owls, the snowy variety are diurnal, or active during the day, which accounts for some of the hubbub. Their blinding white coloring, sometimes with brown barring, and piercing yellow eyes are a magnet for birders and nonbirders alike.

Adding to the allure for children, the owls are of the same species as Hedwig, the faithful companion of the fictional wizard Harry Potter, which perished defending him in the final book of the series.

Geoff LeBaron, director of the Audubon Society’s Christmas bird count, said that it was hard to estimate how many snowy owls flew south in this irruption because the latest data has not been tallied, but that the overall number was probably a few thousand. Despite the surge, the society says, snowy owls are thought to have been in decline since 1945.

There is far more data on the scope of this migration than in years past, thanks to a citizen science project based at Cornell called eBird, which is run by the Cornell Lab of Ornithology and the Audubon Society. Bird-watchers around the country call in sightings, which are plotted on a map that shows precisely where the birds are wintering.

“A lot of people who have never seen one before have rushed out and seen multiples,” said Marshall Iliff, an ornithologist at Cornell and the project’s leader. “And photographers are having a field day.”

Additional hot spots include the mouth of the Columbia River in Washington State, with 10 to 13 birds; 20 at Lake Andes National Wildlife Refuge in South Dakota, and 30 in Boundary Bay, near Vancouver in British Columbia.