UW’s WYOBIRD Contributes to Study on Climate Sensitivity Among Tree Swallows
Published July 10, 2026
Undergraduate students participating in Wyoming Bird Initiative for Resilience and Diversity (WYOBIRD) pose for a photo while banding adult tree swallows. From left are Sarah Peters, Caroline Robbins, Jahshua Sanchez and Chloe Flager-Hess. WYOBIRD and Corey Tarwater (not pictured), a UW associate professor and director of WYOBIRD, were part of a recent research paper titled “Divergent population trajectories despite similar response to temperature in a widespread aerial insectivore.” (Kim Jordan Photo.)
Across the board, tree swallow populations have similar sensitivity to warming amid
climate change, but different abilities to respond to change. Breeding dates have
advanced about one day per degree of warming, but northern populations face tighter
time constraints and greater exposure to warming, according to recent research that
included University of Wyoming students and faculty in the Wyoming Bird Initiative
for Resilience and Diversity (WYOBIRD).
These findings are detailed in the research paper “Divergent population trajectories
despite similar response to temperature in a widespread aerial insectivore,” co-written
by Corey Tarwater, a UW associate professor and director of WYOBIRD, and published
Tuesday, July 7, in the scientific journal Proceedings of the National Academy of
Sciences of the United States of America.
According to the paper, northern tree swallow populations are experiencing the greatest
increases in warming. Even though they show the most advancement in laying dates,
constraints caused by migration make it challenging to shift their timing even earlier,
leading to greater declines in abundance compared to more southern populations.
“More broadly, we show that even species that uniformly respond to temperature changes may vary across populations in their ability to keep pace with climate change,” says Tarwater, who also is the Robert B. Berry Distinguished Chair in Ecology. “We need to understand both species sensitivity to a changing climate and their opportunity to respond to understand the consequences of climate change.”
Climate change is altering animals breeding timelines, the paper says, noting it’s unclear why some populations keep up with warming and others fall behind.
These phenological shifts -- timing changes in biological events such as breeding
or egg laying -- are among the most documented responses to climate change, says Tarwater,
who adds many species are breeding earlier. But there is a sizable variation in how
drastically species shift their timing, with few studies examining how a single species
responds to climate change across its range.
It’s typically unknown whether species differ in their sensitivity to climate change or their ability to act on it, making it difficult to identify the most-at-risk populations, the paper says. Here, the study was able to do this by examining 123 tree swallow populations throughout the U.S. and Canada. As one of North America’s most studied species, the bird’s monitoring history offered researchers an exceptional opportunity to examine populations’ responses to shifting temperatures across an entire breeding range, Tarwater says. The findings regarding tree swallows show populations were equally sensitive to temperature changes but differed in whether they could respond effectively to it.
UW’s involvement in this research began after Conor Taff, the paper’s lead author and a research associate at Cornell University, approached WYOBIRD about contributing tree swallow data from observations at the Hutton Lake National Wildlife Refuge near Laramie. This is the first time WYOBIRD’s work has been published in a research paper.
WYOBIRD is based out of UW, with the goal to “advance knowledge, appreciation and
conservation of birds locally and globally,” according to its website.
To achieve this mission, WYOBIRD conducts novel research; provides students with training
and field experience needed for employment and advanced degrees; and shares science
through public outreach.
WYOBIRD has monitored tree swallows in the Hutton Lake area since 2022, after taking
over monitoring efforts from the Laramie Audubon Society, which began research in
the area in 2017. A total of 30 undergraduate students and five graduate students
have been involved in WYOBIRD’s tree swallow monitoring, with students receiving hands-on
experience monitoring nests, banding nestlings and carrying out behavioral observations.
Chloe Flager-Hess, who participated in the Wyoming Bird Initiative for Resilience and Diversity (WYOBIRD) in 2024, holds a nestling tree swallow before it was banded. WYOBIRD began banding nestlings in 2023 to observe their growth and survival. (Kim Jordan Photo)
“For undergraduate students, this kind of hands-on experience is invaluable. Directly working with birds builds practical skills difficult to teach in standard classrooms and is essential for those interested in a career in ornithology or wildlife biology,” Tarwater says.
Graduate students also play a central role. They gain mentorship experience by guiding undergraduates, while also developing their own research skills.
Their involvement makes it possible to sustain the study each year,” Tarwater adds.
Including WYOBIRD’s data, 1,555 population years from 123 tree swallow populations
were gathered by twenty-eight separate research groups, resulting in 53,375 nest observations
between 1966 and 2024. To be included in the study, data had to cover a total of at
least eight years in one location. The study also utilized citizen-science data from
Breeding Bird Survey, eBird and NestWatch. These volunteer-driven programs are invaluable
for understanding changes in bird populations, Tarwater adds.
The paper has a total of 81 co-authors, including Tarwater and former UW Ph.D. student Sam Case, the first graduate student involved in studying tree swallows through WYOBIRD. Kim Jordan, a former UW master’s student of Tarwater, helped her compile WYOBIRD’s data about tree swallows.
“This study is a powerful example of what becomes possible when researchers collaborate together,” Tarwater says. “As threats to wildlife grow, this kind of collective effort is increasingly essential. This is an important lesson we want to model for the next generation of scientists.”
Undergraduate students involved with WYOBIRD, listed by their hometown and the year
they participated, are:
Bethel Park, Pa. -- Sarah Plotz, 2025.
Brighton, Tenn. -- Megan Van Hoek, 2023.
Broomfield, Colo. -- Therese Turner, 2026.
Casper -- Sammy Vieuther, 2024.
Cheyenne -- Andrew Bishop, 2024; Craig Casey, 2023; Aileen McGahuey, 2026; and Sarah
Peters, 2024-2026.
Chugiak, Alaska. -- Katie Schabron, 2023.
Cody -- Summer Holeman, 2022.
Columbia, Mo. -- Brooke Nieder, 2025.
Coppell, Texas -- Caroline Robbins, 2024-2026.
Dubois -- Jahshua Sanchez, 2024.
Franklinton, La. -- Kyle Sumrall, 2023.
Galesburg, Ill. -- Cora Neal, 2022.
Kealakekua, Hawaii -- Cooper Harbour, 2022.
Laramie -- Josh Donner, 2024-2025.
Lincoln, Calif. -- Presley Wheeler, 2022.
Longmont, Colo. -- Sabrina Johnson, 2026.
Loveland, Colo. -- Skyler Tyson, 2025.
Middletown, Conn. -- Chloe Flager-Hess, 2024.
Orangeburg, N.Y. -- Hudson Urruttia-Orme, 2025.
Palmyra, Pa. -- Devin Gearhart, 2022.
Plainfield, Ill. -- Quinn Herner, 2022.
Riverton -- Emily Roseno, 2022.
Rock Springs -- Chester Townsend, 2023.
Scottsbluff, Neb. -- Kaya Vonburg, 2022.
Sheridan -- Shawna Lacoy, 2022.
South Bend, Ind. -- Sophia Culver, 2023.
Wagner, S.D. -- Cadee Lea Nelson, 2026.
Graduate students involved with WYOBIRD, listed by their hometown and the year they
participated, are:
Burleson, Texas -- Kim Jordan, 2024.
Eden Prairie, Minn. -- Sam Case, 2022.
Dover, Mass. -- Paul Dougherty, 2023.
Montrose, Colo. -- Reina Galvan, 2026.
Philadelphia, Pa. -- Emily Shertzer, 2025.
To learn more about WYOBIRD, visit .
To read the research article, visit .
The University of Wyoming has earned its Research Level 1 (R1) status from the Carnegie Classification of Institutions of Higher Education, placing Wyoming's only four-year university with the top research universities in the United States.