young man attaching a GPS unit on a beaver

Brooks Pitman, zoology graduate research assistant with Southern Illinois University’s Cooperative Wildlife Research Laboratory, works on attaching a GPS unit on beaver at the Union County Conservation Area in Jonesboro, about 45 minutes south of Carbondale. Pitman is tracking the movements of the sleek, water-dwelling mammals in an attempt to better understand their movements in fine detail. (Photo provided)

May 04, 2022

SIU student researches beavers using novel technique

by Tim Crosby

CARBONDALE, Ill. — A student researcher at Southern Illinois University Carbondale is finding out just how busy local beavers can be.

Brooks Pitman, zoology graduate research assistant with SIU’s Cooperative Wildlife Research Laboratory, began tracking the movements of the sleek, water-dwelling mammals in February 2021 in an attempt to better understand their movements in fine detail. Pitman hopes the work, which took place on the Union County Conservation Area in Jonesboro, about 45 minutes south of Carbondale, will lead to better management practices, as well as assist with reintroduction efforts around the country.

Pitman only recently began crunching the large set of data gathered during the previous year, but some results are starting to emerge. It appears beavers’ home ranges are small, in some cases less than a quarter square mile. And even within that limited area, beavers tend to regularly visit only a few locations for long periods of time.

It could indicate beavers busily focus on only small patches of trees and shrubs at one time, until those resources are depleted, said Pitman, who is working under the supervision of Guillaume Bastille-Rousseau, assistant professor of zoology in the Cooperative Wildlife Research Laboratory.

“We are working on developing approaches that will help us digest all the data to learn how factors like resource availability, interaction with other beavers, territorial boundaries and travel distance from a lodge all affect the establishment and structuring of individual home ranges,” he said.

A key wetlands critter

Technically classified as a rodent, beavers play an important role in the health and maintenance of wetland ecosystems. Beavers grow throughout their lifetimes, reaching up to 4 feet in length — including their distinctive paddle-like tails — and on average weigh about 55 pounds, though they can reach twice that weight in old age.

Once over-hunted for their thick pelts, beavers are now commonly found throughout most of the United States. Some Western states have begun reintroducing them to the wild as a means of mitigating the impact of wildfire and drought through their signature activity – dam building.

Beaver dams slow the flow of headwaters, helping to retain water later into the dry season. The dams help create pond and wetland complexes that provide habitat and benefits for themselves and a number of plants and other animal species. The beavers’ selective foraging of trees and plants also helps to shape and maintain healthy plant communities, Pitman said.

Better management needed

While providing many environmental benefits, the beavers’ industrious nature can also lead to problems, Pitman said.

“In some parts of the United States, beavers have become overabundant, and their damming behavior can cause damage when interfering with human infrastructure,” he said. “Given both the positive and negative impacts associated with beaver activity it’s important to develop a better understanding of their behavior, especially of their movement.”

A slippery character

To track an animal in the wild, researchers must find a way to stick to them like glue. Collaring wild animals with GPS units is a tried-and-true method developed over decades. Beavers, however, aren’t your typical subject, and their tapered, tubular shape – an asset for gliding effortlessly through the water – means attaching a collar or even a backpack-style transmitter unit used in some wildlife cases, isn’t possible.

So how do you stick like glue to a wild, water-going animal with no neck? Turns out, you use, well, glue.

“Commons GPS attachment methods are not suitable for beavers, so the first part of our research was testing the use of adhesives to attach the transmitters to their fur,” Pitman said. “We found that gluing GPS transmitters to the fur of a beaver is an effective way of getting highly detailed data on beaver movement over a period of around one to two months,” with the trackers eventually falling off.

Although the beavers tended to focus on a small patch of resources, they also occasionally visited the outer ranges of their territories, suggesting an almost “patrolling” behavior during which they would likely refresh territorial markers. The data may also have revealed travel routes the animals use to reach their foraging areas. So-called “beaver runs,” a section of the floor of a body of water partially excavated to provide a “highway” for the beavers to travel along when moving about their home range, are probably such an example, Pitman said.

Getting the picture

Just as a photograph’s resolution is determined by the number of pixels it contains, Pitman hopes gathering a high number of GPS locations will provide a clearer picture of the beavers’ lives. Pitman tracked the beavers’ movements at very short intervals in a limited geographic area in hopes of discerning their behaviors at a finer scale.

For example, checking a beaver’s position once a day, or every few days, would provide information on dispersal or home range for that individual. But it wouldn’t show the behavior that drives the animal’s dispersal, nor would it identify how resource selection, or territorial boundaries with other beavers, influences the home range size.

During Pitman’s study, however, the animals’ locations were recorded hourly, every day.

“By acquiring locations on an animal every hour, we can begin to explore some of the behaviors that are only detectable on a finer temporal scale,” he said. “This will include data on how beavers are establishing and maintaining their home range, what resources they are selecting for, and how they use the area of their home range on a day-to-day basis, as well as how often they engage in maintaining territorial markers.”

Bringing back beavers

Pitman said the findings might help Western reintroduction efforts, where beaver activities that slow and store water during a drought provide moisture for plants in those areas, making them harder to burn.

“Beavers could be a great ecological tool in battling these environmental issues in the West, but it is generally very costly to perform reintroduction projects, and they are not always successful,” Pitman said.

The study might help wildlife managers select better sites for reintroduction, Pitman said, leading to a better environment for all.

“Not to mention producing another happy colony of beavers doing what they do best: structuring the environment and habitat to not only benefit themselves, but a number of other plants and animals while helping to reduce the impacts of drought and wildfire in the West,” he said.