CHICAGO (AP) — A pair of snowy owls spotted along a Lake Michigan beach has drawn curious crowds and sparked happy speculation about how long the Arctic birds of prey will call Chicago home.

Word of the two owls has circulated on birder forums in the nation’s third-largest city for about a week, according to the Chicago Ornithological Society. While snowy owls aren’t rare in Chicago, their frequency varies widely each winter. Generally, a handful are reported around December, but sometimes there aren’t any.

“Their nomadic nature makes them hard to study or even figure out patterns,” Edward Warden, the society’s president, said Sunday. “Where they’re going is anybody’s guess.”

This year, two birds have been seen at a beach and pier near the Montrose Point Bird Sanctuary on the city’s North Side. A third one was briefly spotted at a beach a few miles (kilometers) south, according to the Chicago Ornithological Society

The pair arrived a bit earlier than the birds usually do and have stayed longer as well, prompting questions about whether this will be the year of a possible “irruption,” or boom migration. In previous years, that’s when a dozen or more have shown up in Chicago.

On Saturday, well over 100 people came out to a concrete pier that juts out into the lake to catch a glimpse. Among them was Sean Clark, a birder and photography enthusiast.

“They were coming and going all day long. It’s amazing that the birds are accepting of that many people,” he said.

The owls did seem rattled, however, by some peregrine falcons that swooped down near them, something Clark was able to capture on his camera. The owls’ yellow eyes grew wide and they flapped their large wings but stayed put.

Snowy owls live north of the Arctic Circle during the summer. In some years, some of the owls stay north while others migrate to southern Canada and the northern half of the United States in the winter, according to experts. On a global scale, they’ve been considered “vulnerable” — one step from endangered — by the International Union for Conservation of Nature.

In Chicago, the birds eat a range of things, including small mammals or waterfowl, according to the Chicago Ornithological Society.

Alan Hougton came to see the owls on Saturday, his first time since he started birding five years ago.

“It was awesome,” he said.

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Slevin reported from Denver.