Leave it to beavers
Coexisting with Montana’s largest rodent
MADISON COUNTY—Beavers may not be the primary animal that visitors to Big Sky Country come to see, but perhaps they deserve a little more attention. After being hunted and trapped to a small fraction of their initially 60-million-strong population in the United States, beavers are making a comeback in Montana, and serving some important ecological purposes as they do.
Best known for their characteristic dams, beavers are often seen as a nuisance by many landowners. However, reports Montana Fish, Wildlife and Parks (FWP), they can also be instrumental in maintaining healthy habitat, wildlife populations and water quality.
Beaver dams can vary hugely in size and can be built anywhere from creekside road crossings to culverts and spanning large waterways. The largest beaver dam in the world was measured at nearly 2,700 feet across. But the vast majority are just large enough to span the width of a creek, and over time the hydrology of the American West has changed significantly because of the dramatic drop in beaver populations.
Torrey Ritter, an FWP beaver specialist, says the streams and rivers in the West look very different than they did before Europeans settled the west and brought grazing animals with them. Once the beaver fur trade took off and trapping and shooting beavers became an integral economic puzzle piece, what were once winding, interconnected waterways with wide floodplains gradually turned into straighter, narrower and faster streams.
“Beavers created this really diverse riparian habitat that all these different species could live in,” says Ritter. “What beavers do is spread water out over a much larger part of a floodplain. It seeps through the system much slower and not only benefits wildlife but also agricultural producers and fishermen. Just having those dams in place slows that water down a lot.”
Beaver dams create wetlands in redirecting the flow of streams, providing healthy habitats for wetland-dwelling species like birds, amphibians and insects. While they’ve been known to use a variety of different tree types to build their dams, they usually focus on quick-growing trees like poplars and cottonwoods. Those types of trees often sprout multiple seedlings from the spot the beaver chops off, meaning that beaver activity can facilitate the growth of new sprouts.
That means healthier soil, more environment-cleaning photosynthesis and better habitat for other animals, including greater green cover for large game like elk, deer and wetland-loving moose.
In addition to helping out native plant species and facilitating regrowth, beaver dams also help preserve water quality and quantity.
The dams, which are porous, act as natural water filters, slowing down streams and helping to remove sediments from fast-moving water. Since the whole point of the dam is to provide a beaver family with a still pool in which to live and hunt for food, slower water means the flow from the other side is cleaner as a result.
Slower-moving water also provides greater recharge for nearby groundwater sources. Since the dammed stream takes less sediment with it and meanders more, it allows for greater absorption into the water table and reduces erosion along nearby banks.
What’s more, Ritter says, is that the sediment-catching properties of beaver dams can help streambeds and waterways return to their historical character.
“All that sediment, rather than being flushed down into reservoirs, is caught behind dams and can help rebuild,” he says. “You end up with these complex, multi-channeled floodplains that provide resources for a really large number of species.”
And, since so much of western Montana’s streamflow comes through mountain snowmelt, beaver dams built in mountain streams help to moderate the rate of flow, meaning more water later into the warmer months.
“Dams in the mountains that slow that down ensure that there are longer flows later into the year,” says Ritter. “There’s more of a buffer between the snow melting off the mountains and droughts later in the year.”
But no matter the benefits, in some situations simply leaving beavers to their own devices isn’t the best technique. Trapping is an option for beaver management, but the state of Montana requires a permit to trap, and there are non-lethal ways to protect nearby trees and waterways from the effects of beaver inhabitation.
Beavers are classified as “furbearing” animals and are thus one of the species that can legally be trapped during the open season, which runs from the beginning of November through April 15 in FWP’s Region 3, which includes Madison and Gallatin counties as well as several other counties in the southwestern part of the state.
“The problem with trapping or shooting beavers is it’s always a temporary solution,” says Ritter. “Beavers will travel to find suitable places, and they’re always going to show up again in good habitats.”
The best management practices depend on what problems beavers are causing, Ritter says. The two he sees most frequently are flooding and tree damage.
To protect trees, FWP recommends loosely wrapping trunks in wire fencing or hardware cloth. For smaller trunks, slicing a length of PVC pipe and wrapping it around the base of the trunk can help prevent damage.
A more creative option Ritter has seen is to paint the bases of trees with a mixture of latex paint and masonry-grade sand, resulting in a texture that beavers don’t like and acting as a repellent. Scented repellents are also an option, but those often need to be reapplied repeatedly.
If downed trees are already present on a property, FWP says leave them there. A beaver, much like a human, will prefer to do as little work as possible and will go for a felled tree before choosing to cut down one that’s still standing. A beaver’s tree felling endeavors generally stay within around 50 feet of a water source, so leaving greenery and growth near ponds and streams can help prevent damage to residential trees.
There are also ways to allow the critters to go about their beaver business, while still preventing property damage or flooding. Flow devices can be installed in streams, especially near culverts or road crossings, to help mitigate the backing up of water due to damming. Ritter uses the brand name: Beaver Deceivers.
These involve threading a flexible tube through notches cut in a dam, then placing a cage around the end of the tube that prevents beavers from plugging the hole. Water flows through the dam and, in most cases, the beavers can still use their home as long as the level of the pond created is still deep enough.
Lining the walls of a ditch or streambank can also help. Beavers sometimes burrow through these while building their homes, and mesh wiring can help to discourage that and preserve the structure of the waterway at the same time.
In the future, Ritter says, there’s also a possibility of using beavers to aid in restoration of Montana’s river drainages. By building small imitation dams, planting willows and releasing beavers into an affected area, allowing them to simply do their job creates a double benefit: helping the beaver population to rebound and providing some relief and healing to damaged waterways.
There are fewer beavers around the Madison Valley than elsewhere in southwest Montana, largely attributable to the rockiness of the area’s streams and the lack of the rodents’ favorite types of trees. But Ritter says the Alder area, the Ruby Valley and especially Hebgen Lake are much more conducive to happy beaver homes, so for a winter beaver-watching expedition, those are the places to look. If you listen close enough, you might be able to hear the sound of teeth munching through willow trunks.