They revolve around chimneys, whirl around and chase each other. They fly through the air and forage on insects and vermin. But when dusk strikes, they go home again. Suddenly they circle in like a cyclone and land in old, high brick chimneys.
“There’s nothing quite like it in nature,” said Nancy Nabak, president of the Wisconsin Chimney Working Group, an environmental advocacy group. “It increases our sense of awe, why we live and the amazing things we’ve experienced.”
As they migrate to South America each fall, chimney swifts gather and plunge down chimneys they use as communal resting places. Each year, groups of birdwatchers gather to watch events called “Swift Night Out.”
Early September, Swift Night Out rallies are held across the state, including in Madison.
Like many bird species, chimney swifts are declining. Their population in Wisconsin has declined by 72 percent in the past 50 years, according to the most recent data from the North American Breeding Bird Survey. While not listed as endangered, their declining population is a concern for scientists and bird watchers.
Experts believe that a decline in insect prey, climate change and a shortage of chimneys are contributing to the declining swift population in several ways.
“It’s a puzzling, probably multifaceted problem, and it’s hard to control, but it’s not just chimney swifts that are declining,” said Anna Pidgeon, a professor of forest and wildlife ecology at the University of Wisconsin-Madison.
“Birds that rely solely on insects for their entire annual cycle for food are declining as a group. Swifts may not be a flagship, but they are an important one,” Pidgeon said. “They are quite striking, and they are also striking in their decline.”
Decreasing insect prey and pesticide use harms swifts
An important factor that researchers are investigating is the swifts’ wilting food source: insects.
Pidgeon noted that when the pesticide DDT was introduced in the late 1940s, the fast diet changed. One study found it “dramatically changed the structure of the insect community in the 1960s, with feeding consequences for swifts and other airborne insectivores.”
The pesticide was banned in 1972. But outside the United States, Pidgeon said the effects of DDT can still be felt as the swifts migrate.
“Some of the countries that the flue goes through quickly on the way to northwestern South America, in the non-breeding season, may still be using DDT,” she said, adding that other insecticides affect different agricultural areas.
Research into the impact of climate change and extreme weather on swifts is ongoing
In addition to a declining insect population, chimney swifts have to deal with a shortage of nest chimneys and extreme weather conditions.
“We have good evidence that pesticides have caused problems, and we suspect that habitat loss and climate change may also be a factor,” said Stanley Temple, professor emeritus at UW-Madison and senior fellow at the Aldo Leopold Foundation.
Since the North American Breeding Bird Survey was first introduced in 1966, chimney swifts have declined by about 2.5 percent each year. In Wisconsin, they are down about 1.5 percent annually.
Nabak, of the Wisconsin Chimney Working Group, said migration is particularly dangerous for the birds and has been made more difficult by climate change.
“It’s a very dangerous time,” Nabak said. “They have to travel thousands of miles, possibly during stormy weather patterns, and there are many documented cases where birds have experienced deaths from a major storm or hurricane or something else.”
Such weather events are becoming more intense and frequent, but Temple said it’s not yet clear whether the chimney’s rapid exposure to them is causing their steady decline. In any case, it could be a “weak” link as other bird species are facing these events but not declining, he noted.
Rather, the real mystery, Temple said, happens during the winter months, when they’re much harder to study.
But one potential problem posed by climate change is a “disconnection” between several extreme weather events, Pidgeon said.
Richard Staffen, a zoologist and conservation biologist with the Wisconsin Department of Natural Resources, said the timing of the rapid migration of the chimney doesn’t always match the peak season to forage insects and feed their young.
He and the Wisconsin Chimney Working Group are urging the public to maintain chimneys and count and log birds they see to help them sustain the population.
Protecting the bird for future generations
Staffen said the DNR is exploring solutions, such as building high-speed towers that mimic chimneys. He emphasized that chimney swifts are unique and interesting birds because they fly to urban areas, where some people don’t have a chance to see wildlife.
“It says something about the health of those urban areas and cities. If there are still good bugs available, there will still be insectivores in the air, like chimney swifts,” he said.
Pidgeon talked about a friend who works for the Forest Service on Lake Superior’s north shore. The local high school planned to remove the chimney, but she worked with them to create a replica and, in turn, a resting place.
In a similar capacity, the Wisconsin Chimney Swift Working Group partnered with the US Fish and Wildlife Service last year to invest in a pilot project repairing a chimney at the Vernon County Historical Museum in Viroqua.
“If we hadn’t, chances are that chimney would have been lost,” Nabak said. “That’s home, that’s the habitat for hundreds of swifts..”
Staffen added that chimney swifts usually nest between May and September, when chimneys and fireplaces are rarely used. He recommended closing the valve on the chimney to keep them from falling down or entering the house.
He and the Wisconsin Chimney Swift Working Group are urging the public to maintain chimneys, count and log birds they see to help them sustain the population.
A “spectacle” worth seeing
To document the number of swifts entering a chimney, the DNR recommends submitting data to eBird.org.
“If you can count, that’s all you need to do. You don’t even need binoculars,” said Nabak of the Wisconsin Chimney Working Group. “Everyone can make a difference.”
While the chimney’s rapid population is declining, many observers still find beauty by watching them flutter to the roosts of chimneys, which attract hundreds to thousands of birds.
Staffen compared it to the ‘old days’, when people imagine clouds of birds flying overhead.
“It’s kind of like that on a slightly smaller scale, but to just see the sheer number of birds that are still there is really cool,” he said.