Tracking Down Nature’s Engineers

Humans sometimes see beavers as a nuisance - damming streams and rivers and creating ponds where there were none before. For the environment, however, they can often be an underappreciated boon. "They're wetland engineers," says Aidan Woods '23. "What they do out of instinct is to create wetlands, which are habitat hotspots for many kinds of wildlife."

Woods recently served as a research assistant for Colgate geography professor Michael Loranty, cataloging beaver populations in upstate New York in order to get a better understanding of how these industrious forest dwellers are distributed in the environment, and what factors determine their prevalence.

"There is an emerging body of research that highlights the ecosystem services provided by beaver wetlands that may be helpful in dealing with the consequences of climate change," Loranty says. "But because these benefits vary geographically, there is a lot of uncertainty related to beaver abundance."

Using 30 years of aerial photography, Woods meticulously catalogued locations of beaver dams in Madison and Oneida counties. He and Loranty describe their findings in a paper published by Northeast Naturalist in June, cowritten with Colgate biology professor Timothy McCay and outdoor education director Heidi Riley. They found that beaver populations have increased dramatically in past years, potentially serving as a bulwark against wetlands at risk of disappearing from climate stress - but their distribution hasn't been equal in all areas.

Loranty has studied beaver populations in Alaska and initiated the current project as a way to examine their distribution closer to home. Woods, a Hamilton native and alumnus of Colgate's geography department, was excited to join the project a few months after graduating in May 2023. "I never got to do this kind of research while I was a student," he says.

Surveying the woods for the presence of beaver dams would have been impossible, but the team was able to take advantage of years of aerial surveys taken from the New York Orthoimagery database. Using surveys from 1994, 2002, 2013, and 2022, Woods diligently examined every lake, pond, and stream in those two counties for signs of beaver activity.

"What you tend to look for is a curvilinear shape across a stream or next to a body of water with a kind of brownish coloration," Woods explains. The curved shape of the dams helped distinguish them from bridges. He was also able to sometimes find additional evidence of dams from the existence of beaver lodges, small mounds of mud and branches nearby. As an additional check, he compared some locations to beaver dams Riley had identified on canoe trips with students near Hamilton's campus.

After several months of diligent tracking, Woods was able to create a geotagged database of thousands of dams over the 30-year period. He and his colleagues found that the number of dams more than doubled over that period, from 972 in 1994 to 2,515 in 2022. "The number of dams increased substantially," Woods says. Most of that growth occurred in areas where beavers were already present, and away from centers of human population. "That's not surprising, since humans aren't as hospitable to beavers, and tend not to like to have them on their property."

What was surprising is that the beavers seemed equally at home in a variety of habitats, including dense forests, open space, and even agricultural fields, suggesting they are more adaptable than previously realized. "Our results raise new questions about what exactly is driving the increase in dam numbers," Loranty says. "This work can inform managers by beginning to establish a catalogue or inventory for dams in this overlooked region."

While these findings only apply to two counties, the techniques the researchers developed could serve as the basis for a wider survey of all of New York State, particularly if they could be automated through artificial intelligence to identify all beaver dams in the state. As ecologists seek to manage beaver populations in the state, such a survey could help them make decisions about wildlife management practices that could help conserve beaver habitat while at the same time helping beavers better live in proximity to human settlements.

"The overall trend across the world is we are losing our wetlands at a measurable pace," says Woods. "While there are definitely a lot of measures in place in states like New York to preserve wetlands, there doesn't seem to be an overall plan in place to manage the beaver population. Ideally, our study could contribute to large-scale studies that could feed into an overall picture of beaver abundance and distribution."