If You Build It, Will They Come?

The newly built tower at the Prairie Ridge Ecostation in Raleigh, North Carolina, offers comfortable accommodations for guests and 5,000 of their closest friends.

Though it’s simply a 30-foot shaft with no windows, to chimney swifts (that’s swifts, not sweeps) the tower is like a five-star hotel. And the scientists who dreamed up the faux chimney are hoping that come spring, flocks of the birds will be checking in (so the researchers can check them out).

It took 15 years for John Connors, Mary Ann Brittain, and John Gerwin, naturalists at the North Carolina Museum of Natural Sciences, to make their bird-tower idea a reality. A local architect drew up the plans pro bono, a local business donated the bricks, and with the support of the Wake Audubon Society, the project broke ground last April. Now they’re just waiting for the birds.

Chimney swift populations have been declining for the past 50 years. The species is notoriously difficult to study, so it’s hard to know for certain what’s driving the drop in numbers, but scientists think it’s likely due to a scarcity of nesting and roosting sites.

Before European settlers cleared the land for homes and farms, chimney swifts resided within the hollow trees of old-growth forests. Fortunately for the birds, urbanization arrived with large, hollow structures of its own—chimneys—and swifts readily adapted to the new digs.

Each spring when chimney swifts return from wintering in the Amazon basin, breeding pairs seek out their own chimney—using gluey saliva to attach their nests to the inside wall. A typical household chimney provides plenty of room for a swift family to grow.

But lately, chimney swifts have had slim pickings in the real estate department. People cap their chimneys to prevent small mammals from entering, modern chimneys often have flues too narrow for chimney swifts to get through, and many heating systems don’t require chimneys at all. “We don’t think of birds being dependent on such a thing,” Gerwin says, but losing manmade habitat can be detrimental to a species that has adapted to an urban environment.

One solution for homeowners is to build DIY chimney swift towers, which function as giant birdhouses. While these structures can support nesting pairs, they’re too small to put up a flock looking for a place to roost.

Roosting flocks depend on industrial-size chimneys—the kinds found on old factories and schools—to accommodate their winged ranks. Big chimneys like these, however, have been getting torn down with increasing frequency as buildings age, so the researchers hope the birds will make do with the tower at Prairie Ridge.

The bird’s breeding season ends in August and September, when chimney swifts begin congregating in preparation for their southward migration. Each night at sunset, a chattering mass of birds gathers above a shared chimney, circling until some invisible signal cues them to tornado down the spout. As the departure date draws closer, the flocks grow and grow—sometimes swelling to thousands of swifts.

It’s easy (and amazing) for city dwellers to witness the spectacle, but it’s been hard for us to learn much about the star performers. The scientists hope their fake chimney will be a real research opportunity.

Chimney swifts spend nearly all their time in flight. They feed and drink on the wing, and they can’t perch—their spindly legs make it impossible. (The swift belongs to the taxonomic family Apodidae, which means “no feet.”) When the birds aren’t flying, they’re literally hanging out inside chimneys. Gerwin hopes that by outfitting his team’s tower with video cameras and a viewing deck, researchers will finally get a good glimpse at the swifts’ more impressive physiological feats.

The birds are skilled fliers that “do things in flight that most air pilots can’t do,” Gerwin says. The bird’s flocking behavior is even being studied by the Navy, which wants to create flight models for drones.

The tower’s creators hope to track the birds using radio-frequency identification in order to learn more about flock dynamics and how swifts spend their winters in South America. Another mystery is the bird’s vision. Chimney swifts go from daylight to darkness in a matter of seconds, and no one knows how their eyes adjust so quickly. If the chimney swifts make the tower their crash pad this spring, perhaps researchers will no longer be in the dark.