The slap of a beaver’s tail against water is one of the most unique and startling sounds in nature.
As the largest rodent in North America, beavers have evolved exceptionally well to their environment, gnawing through willows and trees to create the dams and lodges that mark their territory. Their altering of waterways impacts numerous other fish and wildlife as well.
It was looking for answers to the questions of how beavers select habitat, and what humans might do to encourage them to colonize, that earned Torrey Ritter his master’s degree from Montana State University last year. Now a nongame biologist for Montana Fish, Wildlife & Parks, Ritter and others radio-tagged 55 beavers in southwest Montana to track their movements and learn more about what appeals to the animals when they search for new habitat.
“There were two main components: following them through the dispersal process, looking at new habitats they want, but also the trials and tribulations it takes to start a new colony,” he said. “There’s significant interest in using beavers in (wetland) restoration, establishing them in areas they’ve not been in, and we wanted to figure out how they select new sites in the wild.”
While beavers removing trees and causing flooding may damage infrastructure in some cases, they play the role of habitat creators for a variety of wildlife while also altering streams to provide water storage and recharge groundwater.
“We were doing beaver surveys … and I started to realize there’s a huge number of species we were only seeing in beaver habitat,” Ritter said, which included varieties of waterfowl, songbirds, shore birds and amphibians. “They really create a diverse habitat and (create) all those little ecological niches.”
The benefits beavers can bring have renewed an interest across the West in reintroducing them. Rules vary across states but transplants have been more rare in Montana due in part to the strictness of regulations, Ritter said.
Beavers are managed as furbearers in Montana and can be trapped for much of the year, although regulations vary from the eastern and western part of the state, said Bob Inman, FWP Carnivore-Furbearer Program coordinator.
"Most people in the department I think would agree that we have beaver where they fit on the landscape, even though we do have what is undeniably a liberal season," he said.
As more is known about their ecological role in shaping waterways and even making landscapes more resilient to drought and climate change, FWP has received increasing questions and requests to transplant beavers to new areas.
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“There’s a lot of interest, and people’s first reaction is to start moving beaver everywhere, and that’s not the solution,” Inman said. “If the willows aren’t there, they’re going to move, and if the structures aren’t there to prevent flooding they’re likely to get removed. So the benefits that beaver can provide is not a matter of moving beaver, it’s a matter of preparing the habitat to have beaver come naturally.”
Ritter and others found through the research that when beavers do migrate from their home range they prefer to take up residence in areas already modified by beavers. In areas beavers have not previously occupied, building artificial structures such as lodges or dams can keep beavers from quickly leaving the area.
“They would much rather settle in an area already manipulated by beavers,” Ritter said. “So we’re making the argument based on that observation that if you want beavers to settle, build fake lodges and change the stream from suboptimal habitat.”
Beavers can move a surprisingly long way, even across land. As they start dispersing most settle within a few miles but often move as far as 50 miles – an Alaskan study even tracked a beaver for 186 miles.
The longest dispersal in the southwest Montana study was 27 miles while one of the tracked beavers made nearly 15-mile nightly journeys.
"The main takeaways are that beavers are really good at dispersing and finding habitat to occupy, and areas without beavers may not indicate there are not enough beavers but that habitat may not be readily available," Ritter said.
Mapping the potential for beaver habitat is the goal of the Montana Natural Heritage Program through the University of Montana and Montana State Library. There, analysts are working on the Montana Beaver Restoration Assessment Tool, or BRAT, to examine drainages’ ability to support beavers.
“Beaver habitat parameters are really well known,” said Linda Vance, the project’s senior ecologist. “The model has a number input: reliable water source, vegetation suitable for dam building, vegetation suitable for food, not too wide.”
The tool will provide useful information to biologists as streams may meet most but not all criteria. For example, drainages lacking vegetation could provide opportunities for those artificial dams and lodges.
Utah State University spearheaded the efforts to map the potential of beaver habitat in that state. The program in Montana, which Vance said is going through final development, is an offshoot of the Utah program.
“This kind of modeling is going on across the West with the increasing recognition that beavers capture water and store it for subsequent downstream use,” she said. “We once saw beavers as blocking water flows, but as we’ve learned more there’s been a lot of interest.”