Fall migration is in full swing, and among the birds migrating to warmer climates through and from Wisconsin are Chimney Swifts.
The small, fast-flying birds are known for their cigar-shaped bodies and tornado-like dance they perform in the sky.
Brenna Marsicek is the Director of Outreach with the Southern Wisconsin Bird Alliance, formerly known as Madison Audubon. She says that at dusk, the birds will gather as a flock — sometimes by the thousands — and dive headfirst into a chimney to roost for the night.
Lake Effect’s Xcaret Nuñez spoke with Marsicek for this month’s Chirp Chat to learn more about Chimney Swifts and what’s being done to protect them.
This interview has been edited for length and clarity.
For folks who aren't familiar with Chimney Swifts, can you describe what they look like?
They have a really distinct body shape. Their nickname is ‘flying cigar.’ So if you can picture what a cigar looks like, where it's kind of oval-shaped and stubby, that's kind of what the body of a Chimney Swift looks like. They also have a short tail, and their beaks are short and pointy. They have really long wings for their body size, which helps them be super acrobatic flyers.
Their tiny bills are an indicator of their diet. Usually, birds that have small or shortened, pointy beaks are insectivores, and that's what Chimney Swifts are. They're called aerial insectivores because they eat almost exclusively insects, and they eat almost entirely while flying. They can eat flies and wasps, beetles, mosquitoes… and I recently read that they can use their bills to catch larger insects to eat. But with smaller insects, it just goes straight down the hatch while they're flying. So they fly with their mouths open, and just swallow them while they're flying.
Can you tell me about the migration patterns of Chimney Swifts?
We typically start seeing Chimney Swifts in Wisconsin in April or so — they come from a long ways away. They spend their winters in South America, in the Amazon basin, in countries like Colombia, Ecuador, Peru, and Brazil, and they migrate around 3,000 miles to get to places like Wisconsin for their nesting season. So they spend their summers in the eastern half of the United States, east of the Rockies, more or less, and even into southern Canada. They nest in chimneys and in silos. Originally, they would have nested in a hollow dead tree prior to the construction of all these chimneys. But now chimneys are just kind of the perfect habitat for them, so they often use them for nesting and roosting. So they arrive in Wisconsin in April, spend their summers here, and then, typically, late August through September, is when they migrate back down to the Amazon basin.
You mentioned nesting and roosting — what's the difference between the two?
Nesting is when two adults build a nest, and with Chimney Swifts, that's built on the inside of a chimney. Their nests look like half of a small bowl that you would imagine in your kitchen cupboard. They build that out of twigs and spit, and they stick it to the inside of the chimney, and they lay their eggs and raise their young from this spot. There are other adult Chimney Swifts that will sometimes fly in and out of the chimney to bring food and help with that nesting. But there's only one nest per chimney.
Roosting is different in that's when big flocks of Chimney Swifts will come together and come down from flying and just cling and sleep inside of a chimney for the night. That is typically many, many swifts inside of one chimney per night. They're not raising young. They're just coming together to sleep for the night, probably because with so many of them being in the chimney, they can help each other stay warm and avoid predators. So if there's a flock of hundreds or thousands of swifts, it's power in numbers. It's more challenging for a predator to target one particular bird as it's coming out of the chimney.
Say that someone sees this huge swirl of Chimney Swifts in the sky — are they an abundant species, as people might think?
That's a really important question. Chimney Swifts are not as abundant as they used to be… just this year, they were classified as a tipping point species in the 2025 State of the Birds report. That means that they have lost more than 50% of their population in the last 50 years. Chimney Swifts were specifically classified as an orange alert, which means that they're down by 50% and their declines have sped up a lot in the last 10 years. So that's a really serious problem for Chimney Swifts, and we think it's because they are losing habitat, which is chimneys and other places that they could roost, like hollow trees or silos. These are things that are less abundant on landscapes now than they used to be, and because they're aerial insectivores, and we know that the insect population is down, and as a result, so are the animals that rely on these.
You've listed some of the biggest threats to their population. What are some things being done to help Chimney Swifts?
Fortunately, there are things, and some of it has to do with chimneys. If there are old chimneys that need to be maintained, sometimes that's pretty expensive. So helping fund chimney maintenance and restoration is a great way to keep these large roosting chimneys available to swifts during their migration, so that they can come down and roost.
Home chimneys are a bit complicated because they are often capped to exclude critters like raccoons and birds, and that includes Chimney Swifts, just by default, because once it's capped, the Chimney Swifts can't get in there to nest or to roost. So there are ways to avoid capping that prevent rain from coming in, but allow Chimney Swifts to be able to enter. If you have a chimney that is not capped and not lined with a metal liner, making sure that the chimney is cleaned out or swept during non-nesting periods, in early April or after the summer's end, that's a great way to make sure that the chimney is not full of soot and gunk on the inside walls. That can cause the nest to slip and fall off. Swift Towers is also a concept that allows people to create man-made structures that, ideally, Chimney Swifts would use as a nesting and or a roosting spot.
Another thing that we can do for them is to plant native plants, because native plants support many more insects than ornamental plants do. Along those lines, reducing or eliminating the use of pesticides at home or in areas that we can control is really important for that same reason.
I'd also say that participating in or hosting Swift Night Out events is a really great way to raise community awareness of this important, awesome bird that does this amazing thing and what their conservation needs are. So it introduces people to what these birds are, helps them fall in love with them… and then maybe do some work to help protect them as well.
You can find a Swift Night Out event near you by visiting the Wisconsin Chimney Swift Working Group. You can also find Swift Night Out events by visiting local birding groups like Southern Wisconsin Bird Alliance, BIPOC Birding Club of Wisconsin, Feminist Bird Club – Madison, and Milwaukee Birders.
Chirp Chat’s Bird of the Month for September
“Nighthawks are often flying around in similar areas and at similar times as when Chimney Swifts form a swirling vortex of birds and go into the chimney at night,” Marsicek says. “So when you see a bigger bird that has white bars underneath its wings flying around near Chimney Swifts, that is a Common Nighthawk, and they're also wonderful birds that are really fun to spot.”
