As the sun sets on the campus lakes, hundreds of tiny figures flit, circle and swirl through the sky above Columba Hall. High-pitched chattering calls may be heard as an intricate midair ballet unfolds.
When the last rays of sunlight fade, the figures form into a tornadolike mass. Rapidly they dive into the tall, brick chimney on Columba’s north side, entering one by one until the sky is clear.
The whole scene lasts for about 25 minutes, and then the chimney swifts of Columba Hall are safely settled for the night.
“Swifts are historically a pretty hard bird to study. They spend most of their life flying, and they also fly at high altitudes,” says Charlotte Probst ’22, who studied the Notre Dame swift roost during the birds’ migratory seasons in the spring and fall of 2021 and the spring of 2022.
Each evening as the swifts funneled into the chimney, she counted them. At the height of the spring migratory season in 2021, the Columba chimney drew up to 2,400 birds per night — making it one of the largest reported spring roosts among some 286 sites being monitored in the United States. On May 4 this year, Probst’s count was even higher: 3,037 birds.
In recent years, swift numbers at Columba have peaked in early May and early September.
Chimney swifts are small, sooty gray birds with long, curved wings and short legs. Their body shape leads some bird watchers to refer to them as “flying cigars.” They are incapable of perching upright and cling instead to vertical surfaces when at rest.
The birds have historically roosted in hollow trees. But after the start of the Industrial Revolution and the widespread settlement of North America, swifts adapted readily to roosting inside stone and brick chimneys. They build nests on vertical surfaces out of twigs and saliva.
Swifts are federally protected migratory birds whose summertime breeding grounds span the eastern United States and southern Canada. They winter in South America. Roosts serve as overnight stopover sites during migration seasons — places where the birds rest and forage during their long journey.
Swifts spend nearly all daytime hours flying to catch insects and spiders for food. As sunset approaches, the birds gather — first in small numbers, then in that large, swirling mass.
Inside the chimney, away from the eyes of predators, the swifts cling to the walls with their talons and prop themselves up with the exposed spines on their tail feathers. They huddle together for safety and warmth.
An enthusiastic bird watcher, Probst came across the Notre Dame swift roost by chance. As a teenager growing up near Portland, Oregon, she had served as an Audubon Society of Portland volunteer near a century-old elementary school where thousands of migratory Vaux’s swifts roost in the school’s brick chimney. Area residents often turn out to observe the birds, and Probst served as a community educator, answering visitors’ questions about the birds’ behavior.
When she left home for college, she thought her swift-watching days were over, but the COVID-19 pandemic changed that. During several months of her junior year, students were prohibited from eating meals inside Notre Dame’s dining halls. One evening, Probst and her roommate settled on the edge of St. Mary’s Lake to eat dinner. She looked up and noticed tiny birds wheeling about in a familiar way. A walk around the rear of Columba Hall revealed its massive chimney and confirmed her suspicions of a chimney swift roost on campus.
The biological sciences major began to study the Columba roost as an independent research project, then developed it into her senior thesis, focusing on roosting occupancy and the behaviors of the chimney swift population. Joel Ralston, a biology professor at Saint Mary’s College who specializes in ornithology and ecology, served as her faculty adviser.
Long-term monitoring of roost sites can provide researchers insight into trends. By creating a fuller picture of the birds’ habits, scientists may better identify threats facing the birds and work to protect declining populations, Probst says.
Columba Hall, home today to 26 Holy Cross brothers, is a rambling brick structure that dates to the 1890s but has had many additions. The rear chimney originally vented smoke from coal furnaces, but the hall today is heated by a circulating hot water system. The chimney hasn’t been used for years, making it a perfect home base for the swifts.
Probst became friends with some of the Holy Cross brothers who enjoy watching the birds. She once invited friends, fellow biology students and science faculty to gather for a group swift-watch.
From his fourth-floor room in Columba, Brother Donald Schapker, CSC, has a clear view of the building’s tall brick chimney. He first noticed the swifts circling and settling about 15 years ago, and he’s been observing them ever since.
Schapker, 83, is the most enthusiastic swift watcher in the Columba community. “I just look out my window and watch their comings and goings,” he says. The first time he saw them, he says, “they were circling the roof like crazy. Then it looks like the chimney is a giant vacuum.”
Years ago, he got in the habit of emailing a swift-tracking website each spring and fall to report as soon as he noticed a flock increase that indicated the migration season was underway.
The scene reverses itself at sunrise. When the birds awaken at dawn and start flying out of the chimney it looks “like a pot that is boiling over,” he says.
Probst says the Columba chimney is a notably large roost. It’s important to preserve the chimney as a roost site, she adds, so that it will continue to be available for the thousands of swifts that rely on it throughout the migratory and breeding seasons.
The brothers say they have no plans to remove or cap the chimney, although it was shortened a bit a few years ago when some bricks near the top showed signs of structural instability.
This fall, Probst started graduate school at the University of Michigan. She hopes students and faculty will carry on the chimney swift research she’s started. She remains mesmerized by the habits of these feathered campus visitors.
“They’re charismatic little birds, to be sure,” she says.
Margaret Fosmoe is an associate editor of this magazine. Contact her at firstname.lastname@example.org or @mfosmoe.