Beavers as Garden Pests: How to Coexist With Castor Canadensis
Oh, dam! Are beavers making a mess of your property? Don't just gnash your teeth, do something about it!
Quick Reference
- Species: Castor canadensis, the North American beaver, the largest rodent in North America.
- Size: 34 to 36 inches long, plus a 12 to 18 inch tail; adults weigh 30 to 65 pounds.
- Range: forested regions from Alaska and northern Canada south to central California, northern Mexico, and the Gulf Coast into northern Florida.
- Damage types: flooding from dam building, and tree loss from bark chewing.
- Best fix for flooding: a flow device (perforated pipe through the dam) that keeps the pond usable and the water moving. Consult a wetland commission first.
- Best fix for trees: heavy-duty steel mesh wrap, 4 feet tall, 6 inches away from the trunk.
Wild animals are part of what makes nature so magical, and watching them can be highly enjoyable. While it is important to coexist with animals in relative peace, they can cause countless problems when they take up residence in our homes or gardens. In this series, our Wildlife Management Specialist, Shawn Weeks, will educate us about some common household pests, and share some strategies for keeping them under control without dangerous chemicals.
Today we will look at Castor canadensis, the North American beaver. Few backyard pests reshape a landscape as fast as a colony of beavers moving into your pond, and few are as protected by state wildlife rules. The playbook below combines Wildlife Specialist Shawn Weeks’s field experience with the tactics recommended by state wildlife agencies and university extension services.
Habitat and History
The beaver is the largest of all the rodents found in North America. They grow to lengths of 34 to 36 inches, with tails adding 12 to 18 inches. Adults weigh in at between 30 and 65 pounds. They have webbed, clawed hind feet, a paddle-shaped tail that is hairless and scaled, and thick brown fur that is insulating and waterproof. Males and females are virtually indistinguishable in the field.
The beaver’s range includes most of the forested areas in North America. From Alaska and northern Canada, they reach as far south as central California and northern Nevada, northern Mexico, and across the Gulf Coast into northern Florida. Beavers inhabit rivers, lakes, streams, ponds, swamps, and wetlands. The US Fish and Wildlife Service species profile maps the modern range in detail and confirms population densities in most watersheds are now at or near carrying capacity.
Beavers are best known for their ability to build dams, creating new habitats to suit their needs. At the same time, they provide suitable habitat for other varieties of animals, including insects, turtles, frogs, salamanders, ducks, fish, mink, otters, spiders, rails, bitterns, owls, and flycatchers. Beaver ponds also provide nesting areas for great blue herons and cavity-nesting birds such as wood ducks. These ponds provide fishing, canoeing, and waterfowl hunting opportunities for humans.
Beavers create a dam by cutting sticks and branches with their teeth, then shoving them into the bottom of a stream bed. They then pack mud and other debris on top, adding more sticks and branches as needed until the flow of water is stopped, creating the “pond.” This pond provides the beavers with access to food and protection. Beavers will also dam up man-made ponds, causing problems for landowners. This damming is performed instinctively in response to the sound of running water.
Contrary to popular belief, beavers do not live in their dams. Instead they construct teepee-shaped lodges from sticks, branches, and mud, upstream from the dam. There is a dry chamber in the lodge which creates a place to raise their young, a cover from the elements, and protection from predators.
Beavers are semi-aquatic mammals. They use their large, flat tails to balance when standing, as a rudder when swimming, and as a warning tool, slapping the water when threatened by other beavers. Fat is also stored in the tail to use in winter for energy.
Beavers are active year round, primarily nocturnal, and extremely territorial. They will not tolerate beavers from outside their own colony, which usually consists of an adult pair, two to four kits, and two to four yearlings.
The value of beaver pelts is part of what drove European trappers and fur traders to explore much of what is now the northern United States and Canada. Beaver pelts became the standard for trading between Native Americans and trappers, traders, and settlers. Native Americans used beavers for food, clothing, and medicine. The unrestricted taking of beavers, along with the deforestation of North America caused by European colonization, pretty much eliminated them from much of their range for a time. Trapping and relocating efforts by some states in the early 1900s helped the beaver population grow and expand to its current healthy levels. The National Wildlife Federation species profile puts the current North American beaver population at 10 to 15 million, back from an estimated low of around 100,000 in 1900.
Diet
Beavers feed on leaves, twigs, roots, shoots, and the outer bark of trees and shrubs. Beavers prefer birch, aspen, ash, alder, willow, and apple trees, but they will eat any type of tree and shrub if their preferred diet is not available. During the summer, they will eat water lilies, pond weeds, sedges, and grasses. During the fall, they create a food cache just outside the lodge, storing food for the winter.
Reproduction
Beavers are monogamous, having only one mate during the breeding season, and more often than not, for life. Breeding occurs in mid-winter, with a gestation period of 100 to 110 days. A litter of two to five kits is born in May or early June. Kits are well-furred and have fully developed teeth at birth. They begin to eat vegetation at two to three weeks and are fully weaned at about six weeks. The young remain with the adults until their second year, when they are driven from the colony, forcing them to find a mate and establish their own colony.
Problems, Solutions and Health Concerns
Conflicts between humans and beavers have grown steadily over the years. Humans have aggressively encroached on wildlife habitat, while the beaver population has, at the same time, grown exponentially.
There are two main categories of beaver damage: flooding and tree cutting. Beaver activity can threaten property, agricultural crops, or public health and safety. Their main activity, dam building, can also cause problems for natural resources, such as blocking fish migration and the inundation and siltation of rare plant and animal habitats. They can also cause roadways to flood by blocking storm drainage.
There are no known repellents for beaver, and harassment techniques are not generally effective. The continual removal of dam debris may cause a young, non-established beaver to leave, but it is rare.
Damage from flooding caused by beaver dams can sometimes be mitigated, though. Water level control devices may be implemented in certain situations to reduce flooding to a tolerable level for the landowner, while still maintaining suitable habitat for the beavers. These devices are installed with different materials and techniques, but they all follow the same line of thinking. They all include placing a device, such as a pipe, through the beaver dam. This allows the dam to stay and the water to flow. One could also use a perforated pipe, wooden boxes with mesh bottoms, or perforated aluminum piping. The Beaver Institute flow-device library catalogs the current best-practice designs (Clemson leveler, flexible pipe, castor master) and the wetland-permit questions each one raises. Note: landowners should consult a professional, as well as their local wetland commission, before installing water level control devices.
To reduce damage by beavers to storm drainage systems, try installing a strong woven wire fence in front of culverts, ten to fifteen feet away. This will usually cause beavers to build their dam away from the culvert, allowing water to flow. Factors such as water depth, wetland substrate, and topography should be considered.
The best way to protect trees and shrubs from beaver damage is to wrap heavy-duty steel mesh fencing around the base. It must be installed at least 4 feet high and at least 6 inches away from the trunk to be effective.
Another proven method for managing beavers is trapping. This method speaks more to regulating beaver numbers for healthy populations, though, than it does to water levels and tree decimation. If you remove all beavers from a favorable beaver habitat, others will generally move in to fill the void. The best strategy is to follow the advice above and try to live together in relative peace.
Regional Legal Notes Before You Touch a Dam
Beavers, their dams, and the ponds those dams create are protected under state wildlife codes and federal wetland rules in most of North America. Before pulling a single stick, know the ground rules for your region.
- Northeast US (New England, New York): beaver dams often qualify as regulated wetlands. Contact the town wetland commission before any dam work; permits from the state Department of Environmental Protection may be required.
- Midwest and Great Lakes: beavers are classified as furbearers with regulated trapping seasons. Nuisance-beaver permits are usually available through the state DNR wildlife office.
- Pacific Northwest: Oregon and Washington encourage flow devices over removal, and the Beaver Coalition can advise on cost-shared installations.
- Canada: provincial rules vary. In Ontario and Quebec, the Ministry of Natural Resources requires a permit for any nuisance-beaver work outside the regular trapping season.
- Health note: beaver ponds can carry Giardia lamblia (beaver fever). Never drink pond water without filtering and treating, and wash hands after handling wet equipment.
Frequently Asked Questions
Are beavers protected by law?
In most US states and Canadian provinces, yes. Beavers are classified as furbearers with regulated trapping seasons, and their dams often sit inside protected wetlands. Contact your state DNR or provincial ministry before touching a dam.
What is the fastest way to stop beaver flooding without removing the beavers?
Install a flow device (a Clemson leveler or flexible pipe run through the dam). Water keeps moving at a level you set, the beavers keep their pond, and the flooding stops. The Beaver Institute lists the current best-practice designs.
How do I protect trees from beaver damage?
Wrap the base of each valuable tree in heavy-duty steel mesh fencing, 4 feet high and 6 inches away from the trunk. Sand mixed with exterior latex paint painted on the bark also deters chewing in some regions.
Do repellents or noise devices work on beavers?
Not reliably. No repellents are federally registered for beaver, and harassment tactics rarely last more than a few days before the animals adapt.
Can I trap beavers myself?
In most jurisdictions, no, at least not without a nuisance-wildlife permit. Contact your state DNR wildlife office; they can either issue a permit or refer you to a licensed trapper.
Are beaver ponds dangerous to swim in?
The main concern is Giardia lamblia, commonly called beaver fever. Do not drink unfiltered pond water, and rinse cuts and scrapes with clean water after wading.
What time of year are beavers most active on land?
Late fall, September through November, is when beavers do the most tree cutting to stockpile food for winter. This is when tree-wrap protection matters most.
Shawn Weeks
Shawn is a lifelong New Englander. He lives in Canton, Conn., with his wife Tami, mother, sister, and her three children. He and his wife have two grown children and two grandchildren. Shawn is an avid hunter, fisherman, and gardener. He is also a writer, a nuisance wildlife professional, small scale farmer, and scout leader. You can email him at info@weeksoutdoors.com.
- Shawn Weeks
- Shawn Weeks
- Shawn Weeks
- Shawn Weeks
We have 14 acres, mostly wooded, with a small pond and swamp area. Beavers moved in a few years ago and after the initial “destruction” have greatly improved our pond. It is deeper and clearer and they have removed the excessive growth of water lilies. We’ve also collected some of their cut trees for use as firewood and fence posts.
do you know where i can buy beaver for breeding?
thank you
The beavers caused quite a bit of damage at our cottages last summer & fall.
There were fallen trees across our beaches and wood that had been cut and piled were taken away by beavers (the evidence was there; cut wood was trailed all the way to the beaver house 6 cabins away)
Enjoyed reading about the beavers………We live in the country and have lots of small and large animals…………Moles or goffers . about to take us over……We have as usual about 5or 6 deer. Haven’t seen them lately……… Racoons and lots of rabbits.