Coexisting with Beavers

beaver mother with kit - photo by dpep

The American beaver (Castor canadensis) is a keystone species whose ponds and wetlands help replenish groundwater, serve as buffers against wildfires, and provide habitat for a wide variety of wildlife. Once trapped nearly to extinction, these industrious animals have since made a remarkable comeback. However, tens of thousands of beavers continue to be killed every year, often in response to damage caused when they fell trees or build dams that flood nearby roads or agricultural fields. Fortunately, nonlethal measures such as wire cage fencing, flexible pond levelers, and culvert protectors can be used to protect property while enabling beavers and other species to thrive. For these reasons, AWI works to support and expand the use of these methods throughout the country.

Beavers are skilled engineers, well known for their ability to construct dams to create ponds that offer refuge from predators and serve as pantries to store food. They also build large lodges that provide shelter and a safe place to rear their young. Beavers form monogamous pairs and usually live in family groups of up to eight related individuals, called colonies, consisting of the parents, their young from the previous year and, in the spring, their kits from the current year. The older siblings help with infant care, food collection, dam building, and lodge cleaning. Beavers are well-adapted to their aquatic lifestyles, having large, webbed hind feet, transparent membranes over their eyes that function like goggles underwater, and extremely dense fur that repels water and insulates against the cold. And beavers are famous for their large, flat, scaly tails, which store fat during the winter and can be used to warn family members of danger with a forceful slap against the surface of the water.

Somewhere between 60 million and 400 million beavers are thought to have once inhabited North America’s waterways. Excluding South Florida and the most arid regions of Nevada and Southern California, beavers historically occupied most rivers, streams, and lakes coast to coast, from the US-Mexico borderlands to above the Arctic Circle.

Beginning in the 1500s, however, Europeans began trapping beavers for their fur—particularly the prized underfur widely used at the time to make felt hats. By the end of the nineteenth century, commercial trapping had decimated the population. Across the continent, as few as 100,000 beavers remained. Since then, the population has rebounded to around 10 to 15 million, and beavers today occupy much of their former range—though in far fewer numbers and at lower densities than before.

Beaver range in North America
Approximate historical range of beavers in North America, based on a map produced by the US Fish and Wildlife Service

While they are no longer at risk of extinction, beavers continue to be killed in staggering numbers. Each year, tens of thousands of the animals are trapped, snared, and shot in nearly every corner of the country. Recreational trappers catch beavers for the few dollars their fur and castoreum (a secretion beavers use to mark their territories, and humans use to scent perfume and flavor food) might fetch. Wildlife Services—a US Department of Agriculture program that operates largely under the radar—kills beavers in response to the damage they sometimes cause by felling trees and flooding roads, railroads, and agricultural lands. Most of this killing, however, is cruel, ecologically degrading, and unnecessary.

It is cruel because beavers are often ambushed with steel-jaw leghold traps, whose jaws clamp together with bone-breaking force on their limbs, causing excruciating pain. Beavers are also frequently strangled in neck snares and crushed in body-gripping (Conibear) traps—large, rectangular devices with metal bars designed to slam shut on an animal’s body. Some traps are set specifically to hold beavers underwater until they drown. Because they are physiologically adapted to holding their breath while they dive for long periods, however, death by drowning is a slow process for beavers.

Killing beavers is also ecologically detrimental. Beaver ponds and lodges provide shelter and food for dozens of species of fish, birds, amphibians, reptiles, and mammals, including some listed as threatened or endangered under the Endangered Species Act. Beaver ponds also produce an assortment of aquatic insects and lush riparian vegetation, which serve as food and shelter for dozens of species of waterfowl and migratory birds. Trees killed by flooding attract woodpeckers and provide excellent nesting habitat for many types of birds. Salamanders, frogs, newts, and toads use beaver ponds as breeding habitat. Dozens of fish species have been documented in beaver ponds. Moose are attracted to willows that flourish in beaver-created wetlands.

In addition to creating wildlife habitat, beaver-altered landscapes provide other important ecosystem services. Studies indicate that beaver-dammed riparian areas are three times more resistant to fire than surrounding areas and can provide refuges for wildlife during and immediately after wildfires. Beaver ponds help mitigate the negative effects of climate change by lowering overall stream temperature and storing water that can be accessed by animals and vegetation during times of drought. Beaver dams can also improve water quality by reducing sedimentation and removing toxins from the water column.

Beavers’ central role in building and maintaining the wetland ecosystems that serve so many other species—including humans—explains why they are so commonly recognized as “keystone species” and “ecosystem engineers.”

photo by Joe Wheaton
Beaver wetland in southcentral Idaho following a wildfire in 2018. Photo by Joseph Wheaton, Utah State University.

Killing beavers not only raises welfare and ecological concerns, but also is rarely, if ever, necessary. First, fur trapping today is predominantly a recreation, not a livelihood. In a nationwide 2015 survey conducted by the Association of Fish and Wildlife Agencies, 78 percent of trappers said it was “not at all important” as a source of income.

Second, beavers do not need to be killed, or dams destroyed, to protect property. Trees can be shielded by encircling them with wire mesh fencing or coating their trunks with a mixture of paint and sand that deters beavers from chewing. Roads, crop fields, and other human property can be protected from flooding caused by beaver dams through the use of flow devices—systems of pipes and fences that allow a certain amount of water to flow through the dam, thus maintaining the pond at a level acceptable to humans yet still beneficial to beavers and the myriad species that use beaver-created habitat.

Flow devices can also prevent beavers from plugging culverts (pipes that funnel water under roads and railroads). Culvert-protective fencing has repeatedly proved effective at preventing beaver-caused blockages. Several studies indicate that heavy-duty wire mesh fencing installed in a rectangular or trapezoidal configuration upstream of the culvert provides a durable solution.

These measures are not only dependable, but also more effective in the long term because, inevitably, beavers come back. As the Oregon Department of Fish and Wildlife explains, “Removing beavers is often a short-term solution as other beavers will move into the area if suitable habitat is present.” They also rebuild, as the same document notes: “Generally dam removal is a futile effort because beavers will quickly rebuild the dam, sometimes overnight.”

Yet another advantage of flow devices is that they can be more cost effective than lethal methods. A study conducted in Virginia compared the costs of repairing road damage caused by beavers at 14 sites before and after the use of flow devices. The authors calculated that the “before” costs of preventive road maintenance, damage repairs, and lethal removal of beavers was more than $300,000 per year. By contrast, the report concluded that the costs of installing flow devices involved a single expense of less than $45,000 and maintenance costs of just $277 per year. Moreover, the flow devices provided more protection: Before their installation, flooding and road damage occurred annually; three years after their installation (when the study concluded), no flooding or road damage had yet occurred.

Photo by Beaver Institute
Pond leveler. Photo courtesy of Beaver Institute.
Photo by Beaver Institute
Culvert-protective fencing. Photo courtesy of Beaver Institute.

To help promote the use of such ethical, ecologically responsible, and affordable solutions, AWI has long supported the efforts of the Beaver Institute, a Massachusetts-based nonprofit organization that educates the public about how beavers benefit ecosystems, works with landowners and local governments to install flow devices and other preventive measures, and trains wildlife professionals how to properly install and maintain them.

AWI is also working to develop a federal program that would provide states, tribes, agencies, local governments, landowners, conservation organizations, and others with resources to implement nonlethal beaver-conflict solutions. We envision such a program would help make flow devices and other mitigation measures easily accessible to rural and urban communities across the country desiring to live with, rather than in conflict with, their flat-tailed, dam-building neighbors.

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