MONROE — Thousands of Vaux’s swifts are expected to return to the Wagner Center chimney here Saturday as they migrate south for the winter.

Monroe Swift Night Out will be held from 4 p.m. until dusk Saturday at the Wagner Center, 639 West Main Street. Admission and parking are free.

Monroe boasts one of the largest congregations of Vaux’s (pronounced “voxes”) swifts in North America.

The tiny birds are the West Coast version of chimney swifts. They sleep in the chimneys as they migrate north for summer and south for winter.

In minutes, more than 26,000 Vaux’s swifts were seen piling into the 31-foot-tall, 4-foot-square Wagner Center chimney in September 2007. That’s the highest number of the birds that have been observed going into a West Coast chimney, said Larry Schwitters.

Schwitters, of Issaquah, counts Vaux’s and records the numbers almost every night during the migration seasons. “I love it,” the 74-year-old said. “While some people want to see Taylor Swift, I want to go see these swifts.”

The Wagner Center chimney is among four sites in the state that attract high numbers of Vaux’s swifts.

“There aren’t a lot of chimneys in North America that host a lot of these birds,” said Schwitters, who runs a website dedicated to the birds.

There was little information about Vaux’s swifts before the Eastside, Seattle and Pilchuck Audubon societies became interested in the birds several years ago, he said.

The groups raised money to save the Wagner Center chimney from being torn down so they could continue to study the birds. They also came up with other projects to help swifts.

The event Saturday will include booths with nature displays, wildlife education and children’s activities. The Seattle Audubon allows people to touch bird skins and to compare the sizes of different species. Docents will be present to answer questions about swifts.

A spaghetti and salad dinner is available for $6. Proceeds benefit swift research. Hot dogs, desserts, snacks and beverages will also be offered.

People are encouraged to bring blankets and folding chairs to watch the aerial performance.

“It’s a spectacular wildlife encounter,” Schwitters said. “And it’s free.”

Amy Nile: 425-339-3192; anile@heraldnet.com. Twitter: @AmyNileReports