Where Do Vaux’s Swifts Spend the Night? A Community Science Effort Is Mapping Their Roost Sites

A blocky building on the University of Oregon campus. A brickyard in California’s Bay Area piled with neat stacks. A former sugar plantation outside Mexico City with the air of a crumbling castle.

During migration season, these sites, and many more, serve as temporary homes for the Vaux’s Swift, an acrobatic flier with a tube-shaped body. The birds pile into communal roosts to spend the night in chimneys, smokestacks, and hollow trees along the Pacific Flyway. For nearly 20 years, a network of volunteers has tracked birds at these rest stops as part of Vaux’s Happening, a community science project to monitor roosts. They’ve tallied 31 million swift sightings to date from western Canada to central Mexico, says Larry Schwitters, who runs the grassroots effort with support from the Pilchuck Audubon Society in Washington State. 

The initiative started with a single roost in an unused elementary school building in Monroe, Washington. In 2007 the district planned to demolish the building’s defunct chimney, citing earthquake safety concerns. But locals knew that the brick structure sheltered Vaux’s Swifts. “They would tell the kids to bring sweaters to school, because they weren’t going to turn the boilers on until the birds left for the morning,” says Cathy Clark, a Pilchuck Audubon volunteer who’d heard stories from long-time residents.

Members of multiple Audubon chapters and others in the community rallied to save the roost—organizing events to raise awareness, appealing to the state legislature for money to update the building, and counting how many swifts made use of the site. They gathered enough support and funding to keep the chimney up and even place cameras inside to spy on the hordes of birds within. Now the roost is a point of local pride, drawing thousands of swifts per night when migration peaks, typically in late May and early September, plus hundreds of fans to annual Swifts Night Out celebrations. 

“It’s better than any TV show. After all the swifts go in, everybody is clapping and cheering,” says Eileen Hambleton, who has helped organize events over the years. “It’s fun to see people get excited about something in the natural world.”

For Schwitters, who got into studying swifts after retiring from a science teaching career, saving the Monroe chimney was just the beginning. He started reaching out to birders in Washington, and eventually well beyond, with a challenge: “See if you can find me a roost site.” Reports of swifts swirling into schools, churches, factories, and apartment buildings rolled into his mailbox.

These days, Schwitters receives hundreds of online reports from volunteers who spend their spring and fall evenings counting birds at dozens of locations. He compiles the tallies into massive spreadsheets that spotlight key roost sites on the birds’ journeys between breeding grounds in the Northwest and nonbreeding ranges in Mexico and Central America. (As for counting up dizzying numbers of swifts, methods vary; some volunteers use clickers, while Clark studied photos where she circled and estimated groups of 10.) 

The Vaux’s watchers have successfully advocated to save several chimney roosts from being torn down. They’ve also uncovered insights about the species’ behavior by recording the birds with microphones and temperature sensors—such as the fact that roosting swifts are “making all kinds of weird noises all night long,” Schwitters says, and that the inside of a chimney where swifts roost can be a staggering 25 degrees Fahrenheit warmer than the air outside.

The group’s latest focus has been on swifts south of the U.S. border. After years of searching, in 2023, bird guides and locals working with Vaux’s Happening discovered a massive roost in Oacalco, Mexico: an old hacienda with two tall chimneys, where watchers have counted more than 250,000 swifts in a single night. “It’s just the whole sky covered with birds,” says Kashmir Wolf, who helped locate the roost while working for the conservation group Pronatura Veracruz.

As a real estate developer has bought up the surrounding land to build housing, the swift lovers are working with the company in the hopes of keeping the chimneys intact. After all, this place is linked with all the other spaces that shelter swifts; if one disappears, it’s a blow felt across the flyway. “Every single site—every single protected land that we can achieve—is going to make a huge difference,” Wolf says.

This story originally ran in the Spring 2026 issue as “Short-Term Stays.” To receive our print magazine, become a member by making a donation today.