Threats to Vaux's Swifts

Vaux's Swifts have declined steadily for decades. Since 1970, populations in Oregon and Washington have dropped by roughly half, a loss of 2 to 4 percent a year. The species isn't federally listed as threatened or endangered, but the trend line is clear, and it's driven by several overlapping pressures.

Loss of Old-Growth Nesting and Roosting Trees

Vaux's Swifts evolved alongside old-growth forests. Historically, they nested and roosted almost exclusively in large hollow trees, entering through broken off tops or openings originally excavated by pileated woodpeckers. Without those cavities, swifts have nowhere to go: they can't excavate their own nest sites.

Decades of logging removed much of this habitat across the Pacific Northwest, and population declines through the 1970s and 80s tracked closely with the pace of old-growth harvest. What remains is a fraction of the historic supply of nesting and roosting trees, concentrated in the older stands that still have snags and hollow giants standing.

Disappearing Chimney Roosts

As old-growth habitat shrank, swifts adapted by using large brick chimneys as substitute roost and nest sites, especially during migration, when thousands of birds may funnel into a single chimney each night. Only chimneys built before roughly 1940 work for this: newer chimneys are lined in a way that gives the birds nothing to cling to.

Those older brick chimneys are now disappearing too. Redevelopment, seismic retrofitting requirements, and complaints about noise or droppings have led building owners to tear chimneys down or cap them, closing off roost sites that in some cases hosted tens of thousands of birds. When a major roost is lost, there's often no comparable structure nearby to replace it, and the flock has to find a new site or risk having nowhere safe to spend the night.

Declining Insect Prey

Vaux's Swifts are aerial insectivores. They feed exclusively on flying insects and spiders caught on the wing, and their fortunes are tied directly to the abundance of that prey. Aerial insectivores as a group are declining sharply across North America, and agricultural intensification, pesticide use, and broader insect decline are all contributors.

The evidence directly linking swift declines to insect abundance is still developing, but the mechanism is intuitive: fewer insects in the air means less food available during the energetically demanding stretches of breeding and migration.

A Shifting Climate

Climate change affects swifts on multiple fronts. Warmer, more erratic spring weather brings more cold snaps and prolonged rain, both of which can be lethal to nestlings and reduce the flying insects that parents depend on to feed them. Over the longer term, climate models project that Vaux's Swift breeding and migration ranges will keep shifting as conditions change, adding another layer of uncertainty to an already stressed population.

Predation at Roosts

Communal roosting protects individual swifts through sheer numbers, but it also concentrates the entire flock in one place at one time, which predators can exploit. Roost sites regularly draw the attention of Cooper's Hawks, Merlins, and American Crows, which key in on the nightly spectacle and pick off birds as they funnel into the chimney or tree.

What You Can Do

• Report roost sites. If you find swifts using a chimney or tree, let us know. Documenting active roosts is the first step in protecting them.

• Speak up before a chimney comes down. Building owners and cities don't always know a chimney is in active use. A quick note from a local resident can be the difference between demolition and preservation.

• Join a count. Vaux's Happening depends on community scientists who show up at dusk during migration season to count birds entering local roosts. No experience necessary.

• Support habitat protection. Advocate for retaining large hollow trees and snags in local forest management decisions, both on public land and in your own neighborhood.

• Give to Pilchuck Audubon. Roost monitoring, chimney advocacy, and habitat work all depend on support from people who care about keeping this migration spectacle alive.