Understanding the Movement and Space Use of Beavers in Southern Illinois

From the smallest insects to largest mammals, movement is a key behavior organisms use to interact with the world around them. All living things must move to access resources, avoid risky situations, and interact with other individuals. Studying animal movement can therefore provide the unique opportunity to see how organisms are interacting and responding to their surroundings. In the face of an ever-changing environment, understanding animal movement is critical for the conservation and management of wildlife populations.

GPS technology has quickly become researchers’ primary tool to study animal movement. Over the last 30 years, GPS transmitters have improved greatly regarding their accuracy, battery life, durability and size, meaning we can now track a wider array of species. However, there are still some species that remain difficult for wildlife ecologists to track.

Semi aquatic species, such as river otters and muskrats, provide unique challenges which make them harder to study. GPS collars, the most common transmitter attachment method, are not suitable for animals with tapered necks as the collars can easily slip off. In addition, the fact that these animals spend time swimming underwater around various debris also makes attaching transmitters with straps very risky given the chance an animal could become entangled and potentially drown.

Another semi aquatic species that is difficult to track is the North American beaver (Castor canadensis). Easily identified by their paddle-like tail and large teeth, these animals historically inhabited much of North America. However, due to excessive fur trapping during the 1700s and1800s, beavers were largely extirpated from the eastern United states as well as other portions of their range by the early 1900s. To reverse this rapid population decline, wildlife managers implemented harvest and trapping restrictions while also conducting translocation efforts to support the recovery of this species. Today, despite much of their habitat being lost to anthropogenic development, beavers have proven highly adaptable by recolonizing much of their former range.

Beavers are considered ecosystem engineers due to the strong impact their activity has on the habitat around them. By damming streams, beavers help create pond and wetland complexes, as well as alter the vegetative structure which benefits several other plants and animals. Because beavers have such a large impact on their ecosystem, understanding how they move and what influences those movements is extremely valuable information for wildlife conservationists and managers. However, the challenge of figuring how to track such creatures remains.

Since 2021, we at the Cooperative Wildlife Research Laboratory at Southern Illinois University-Carbondale have been working on identifying the best method of GPS transmitter attachment for beaver in order to gain a better understanding of their movement patterns. Our research was conducted on the Union County Conservation Area in southern Illinois, just east of the Mississippi River. We tested different GPS attachment methods for beavers during the spring and fall of 2021 and evaluated which method lasted longest on the animal and provided the most data. We also analyzed the data that was collected through these efforts to evaluate how beavers were moving at a fine-scale.

We compared three attachment methods; a tail-mounted transmitter, a transmitter glued on the lower back of a beaver and a transmitter glued on the upper back. The tail-mounted transmitters were found to be ineffective because the location of the transmitter on the tail resulted in these units staying submerged for much of the time they were attached, limiting the opportunities to acquire a successful GPS location. Glued-on transmitters, however, were more successful in acquiring GPS locations as beavers tend to swim at the surface with their back slightly protruding from the water. Between the two glued-on attachment methods, it was found that those glued to the lower back outperformed those on the upper back. Overall, these glued-on transmitters allowed the tracking of these animals for one to two months.

These data also revealed interesting facts about beaver movement. We found that there were a few central locations that were heavily used by our tagged individuals, generally being associated with a den, lodge or foraging patch. The data also showed that when accessing these central hubs beavers generally used the same pathways to move between them. These central hubs and preferred movement paths made up most of the locations we collected, and we found that only on rare occasions did beavers take a break from the daily tasks to wander away and explore new areas. Finally, we noticed that in our densely populated study area, beavers maintained a buffer between their daily activity and that of neighboring colonies, suggesting these animals do their best to be respectful of their neighbor’s space.

Our research showed that it is possible to track beavers at a fine-scale. The opportunity to track beavers and other semi aquatic mammals to learn about how they move is exciting as it allows new questions to be asked and explored. There is much to learn about how and why beavers move, especially given the important role they play in their ecosystem. Our research takes the first few steps towards developing a better understanding of beaver movement, opening the door for further studies interested in exploring how these industrious little critters behave when no one is watching.

---

Brooks Pitman is a Master’s student in the Cooperative Wildlife Research Lab at Southern Illinois University. He is researching beaver space use and movement ecology in southern Illinois.

Dr. Guillaume Bastille-Rousseau is an assistant professor with the Cooperative Wildlife Research Laboratory of SIU. His research focuses on the spatial wildlife ecology of terrestrial species, mostly focusing on animal movement.