A young snowy owl spent most of the daylight hours Tuesday atop roofs on Pittsburgh's North Side, attracting small crowds of birders and nature lovers.

Snowy owls usually live north of the Arctic Circle, but someone spotted this one atop the Graybar Electric building on Ridge Avenue and called the National Aviary about 10 a.m. Tuesday.

Steve Sarro, director of animal programs at the aviary, said people often provide false leads, mistaking a rare bird for a more common one. Mr. Sarro figured this would be a red-tailed hawk or a barn owl.

But it was unmistakably a snowy owl. Its chocolate-colored barring has Mr. Sarro believing it was a young female. It was probably driven south by older birds when prey grew scarce up north. The bird eats lemmings, hares and small rodents.

Mr. Sarro and Erin Estell of the aviary ascended the roof with nets, and Ms. Estell could have netted the bird as it focused on her colleague, but she decided to leave it alone because it didn't appear to be hurt. After the owl turned to look at her, Mr. Sarro said, it calmly flew off -- "owls don't do anything hurried'' -- and flapped a couple of blocks northeast to the Calvary Methodist Church at the corner of Beech and Allegheny avenues.

The owl stayed atop that roof, harassed occasionally by crows, into the evening as birders and residents of the Allegheny West neighborhood came out with binoculars to get a close look.

The owl was gone by yesterday morning. It prefers to travel by night to avoid harassment in flight by crows and ravens, Mr. Sarro said.

He guessed that it had come from farther south, following the Monongahela River to get to the city and, with the days getting longer and warmer, "This big girl is heading north.''

A snowy owl spent most of the winter in northern Cambria County this year, but no such owl had been seen in Pittsburgh since Nov. 16, 2001. Chuck Tague, a birder from Mount Washington, came down to the Duquesne University campus to join a crowd of about 100 watching that one, he remembered yesterday. The owl had been sighted on the roof of Kaufmann's department store two days before.

Twenty years earlier, on Super Bowl Sunday, Jan. 25, 1981, two city patrolmen netted one in the abandoned Sheridan Square Theater in East Liberty. It was later released in northwestern Pennsylvania.

A snowy owl might show up in Pittsburgh every 10 or 15 years, said Stephen P. Rogers, collection manager for the Carnegie Museum of Natural History's Section of Birds.

"In a year when rodents aren't doing so good up north, they'll come south,'' Mr. Rogers said, "they'll come south.''