If your house has a brick chimney, you may have some unexpected bird visitors this summer. But please don’t shoo them away.

“If it were me, I would say enjoy listening to them,” said Greg Harber with Alabama Audubon, the local chapter of the national birding group. “Nature is providing you a nice insect/mosquito control mechanism.”

These little birds, chimney swifts, are sometimes called “flying cigars” or “cigars with wings.” Only around five inches long, the birds have short tails and blunt heads. They are gray, with a patch of white on their necks.

If you have a chimney swift family nesting in your chimney, it’s best to just leave them alone, Harber said. The birds will eat insects that come in through the top.

The birds are common throughout Alabama during the summer, as well as the rest of the eastern U.S.

Chimney swifts used to nest in hollowed-out trees. But as the U.S. began urbanizing and those trees became less common, the birds adapted.

Unlike most birds, chimney swifts are not able to perch on tree branches or other horizontal structures, Harber said. Instead, they have to cling to something that’s vertical.

During the summer, a pair of swifts will find a suitable chimney. Then, they will gather twigs and make a nest, using their saliva as an adhesive. Rather than a cup, the nest is more like a small shelf on the wall of the chimney.

“You can usually hear their little chirping noises in the chimney. And if they nest in there, well, then you’ll hear the little babies as well,” Harber said. “If you’re fortunate to have one that’s nesting in your chimney, it’s a really a unique experience for sure.”

Chimney swifts migrate south for the winter, catching insects in their mouths as they fly, according to the Audubon Society.

Their greatest spectacle comes during their fall migration, which begins as early as July.

At sunset, a flock of chimney swifts flying south will look for a place to roost for the night. When they find a suitable chimney, they’ll begin to swarm around it, in something Harber calls a “swift-nado.”

Just after the sun sets, the first swift descends into the chimney, and all of the other birds follow. Within minutes, hundreds or even thousands of the birds have all landed in the chimney to rest for the evening before continuing their journey.

“They really are just spectacular sights to see,” Harber said. “It’s the cheapest entertainment in Birmingham.”

Harber said he’s seen the “swift-nado” at a chimney near Legacy Arena and the BJCC in Birmingham. He recommends looking for chimneys at old school buildings to try to see the swift-nado for yourself.

After they migrate south for the winter, the chimney swifts will settle in the upper Amazon River Basin, in Brazil, Peru and parts of Ecuador. Starting in March, the birds will begin migrating north, according to the Audubon Society.

Harber said to expect them on the coast by mid-March, and in Birmingham by early April.

As chimneys fall out of fashion, the chimney swift population is declining. The bird’s population likely increased when chimneys were built in the U.S., according to Cornell University. But modern chimneys are not suitable for the birds, and homeowners sometimes cap their old chimneys, leading to a decline in the bird’s habitat.

Chimney swifts are considered to be at an “orange alert tipping point,” according to the university’s 2025 state of the birds report. The species’ population has declined by a cumulative 74% from 1966 to 2023, according to Cornell, or an estimated 2.3% per year during those 57 years.

Now is the time to act to take measures to conserve the chimney swift, Harber said, while the birds are still relatively common.

“If you see one of these spectacular ‘swift-nado’ formations, you might be inclined to think, ‘There’s lots of them, there’s plenty of them, they’re not in danger,’” Harber said. “Now that we’re aware of this, we can take proactive steps to make sure that our chimneys are kept open and available to them or we can put up chimney swift towers.”