Beavers - Living with Wildlife |  Washington Department of Fish & Wildlife
Beavers
For more information on the Living With Wildlife series, contact the WDFW Wildlife Program
360-902-2515
See also: Beaver Management
Beavers (Castor   canadensis) are the largest living rodents in North America, with adults   averaging 40 pounds in weight and measuring more than 3 feet in length,   including the tail. These semi-aquatic mammals have webbed hind feet, large   incisor teeth, and a broad, flat tail.
Once among the most widely   distributed mammals in North America, beavers were eliminated from much of their   range in the late 1800s because of unregulated trapping. With a decline in the   demand for beaver pelts, and with proper management, they became reestablished   in much of their former range and are now common in many areas.
Beavers are found where   their preferred foods are in good supply—along rivers, and in small streams,   lakes, marshes, and even roadside ditches containing adequate year-round water   flow. In areas where deep, calm water is not available, beavers that have enough   building material available will create ponds by building dams across creeks or   other watercourses and impounding water.
Beavers dams create habitat   for many other animals and plants of Washington. In winter, deer and elk   frequent beaver ponds to forage on shrubby plants that grow where beavers cut   down trees for food or use to make their dams and lodges. Weasels, raccoons, and   herons hunt frogs and other prey along the marshy edges of beaver ponds.   Migratory waterbirds use beaver ponds as nesting areas and resting stops during   migration. Ducks and geese often nest on top of beaver lodges since they offer   warmth and protection, especially when lodges are formed in the middle of a   pond. The trees that die as a result of rising water levels attract insects,   which in turn feed woodpeckers, whose holes later provide homes for other   wildlife.
Figure 1. The   beaver’s incisors (front teeth) are harder on the front surface than on the   back, and so the back wears faster. This creates a sharp edge that enables a   beaver to easily cut through wood.
(From Christensen and Larrison,   Mammals of the Pacific Northwest: A Pictorial   Introduction.)
The beaver’s incisors (front   teeth) are harder on the front surface than on the back, and so the back wears   faster. This creates a sharp edge that enables a beaver to easily cut through   wood.
Like many   rodents, beavers construct nesting dens for shelter and for protection against   predators. These may be burrows in a riverbank or the more familiar lodges built   in the water or on the shore (shown here). However, the basic interior design   varies little and consists of one or more underwater entrances, a feeding area,   a dry nest den, and a source of fresh air.
Facts about Washington’s   Beavers
Food and Feeding   Habitats
Beavers eat the leaves,   inner bark, and twigs of aspen (a favorite food), alder, birch, cottonwood,   willow, and other deciduous trees. Beavers also eat shrubs, ferns, aquatic   plants, grasses, and crops, including corn and beans.
Coniferous trees, such as   fir and pine, are eaten occasionally; more often, beavers will girdle and kill   these trees to encourage the growth of preferred food plants, or use them as dam   building material.
Beavers have large, sharp,   upper and lower incisors, which are used to cut trees and peel bark while   eating. The incisors grow their entire lives, but are worn down by grinding them   together, tree cutting, and feeding. (Fig.1)
Fermentation by special   intestinal microorganisms allows beavers to digest 30 percent of the cellulose   they ingest.
When the surface of the   water is frozen, beavers eat bark and stems from a food “cache” (a safe storage   place) they have anchored to the bottom of the waterway for winter use. They   also swim out under the ice and retrieve the thick roots and stems of aquatic   plants, such as pond lilies and cattails.
Food caches are not found   consistently where winters are comparatively mild, such as in the lowlands of   western Washington.
Click to enlarge
Figure 2. Like many   rodents, beavers construct nesting dens for shelter and for protection against   predators. These may be burrows in a riverbank or the more familiar lodges built   in the water or on the shore (shown here). However, the basic interior design   varies little and consists of one or more underwater entrances, a feeding area,   a dry nest den, and a source of fresh air. (Drawing by Jenifer   Rees.)
Beaver Dams
Beavers flood areas for   protection from predators, for access to their food supply, and to provide   underwater entrances to their den. Flooded areas also wet the soil and promote   the growth of favored foods (Fig. 3).
Beavers living on water   bodies that maintain a constant level (e.g., lakes, large rivers) do not build   dams.
Dams are constructed and   maintained with whatever materials are available—wood, stones, mud, and plant   parts. They vary in size from a small accumulation of woody material to   structures 10 feet high and over 165 feet wide.
The feel and sound of   flowing water stimulate beavers to build dams; however, they routinely let a   leak in a dam flow freely, especially during times of high waters.
Beavers keep their dams in   good repair and will constantly enlarge the dams as the water level increases in   their pond. A family of beavers may build and maintain one or several dams in   their territory.
In cold areas, dam   maintenance is critical. Dams must be able to hold enough water so the pond   won’t freeze to the bottom, which would eliminate access to the winter food   supply.
Lodges and Bank Dens
Depending on the type of   water body they occupy, beavers construct freestanding lodges or bank   dens.
Lodges and bank dens are   used for safety, and a place to rest, stay warm, give birth, and raise   young.
Freestanding lodges are   built in areas where the bank or water levels aren’t sufficient for a safe bank   den.
Lodges consist of a mound   of branches and logs, plastered with mud. One or more underwater openings lead   to tunnels that meet at the center of the mound, where a single chamber is   created.
Bank dens are dug into the   banks of streams and large ponds, and beavers may or may not build a lodge over   them (Fig.2). Bank dens may also be located under stumps, logs, or docks.
One family can have several   lodges or bank dens, but will typically use only one den during winter.
Reproduction and Family   Structure
A mated pair of beaver will   live together for many years, sometimes for life.
Beavers breed between   January and March, and litters of one to eight kits (average four) are produced   between April and June. The number of kits is related to the amount of food   available (more food, more kits), and the female’s age.
The female nurses the kits   until they are weaned at 10 to 12 weeks of age.
Most kits remain with the   adults until they are almost two years old. (Some leave at 11 months and a few   females may stay until they are three years of age.) The kits then go off on   their own in search of mates and suitable spots to begin colonies, which may be   several miles away.
Beavers live in colonies   that may contain 2 to 12 individuals. The colony is usually made up of the adult   breeding pair, the kits of the year, and kits of the previous year or   years.
Populations are limited by   habitat availability, and the density will not exceed one colony per ½ mile   under the best of conditions.
Mortality and Longevity
Because of their size,   behavior, and habitat, beaver have few enemies.
When foraging on shore or   migrating overland, beavers are killed by bears, coyotes, bobcats, cougars, and   dogs.
Other identified causes of   death are severe winter weather, winter starvation, disease, water fluctuations   and floods, and falling trees.
Humans remain the major   predator of beavers. Historically, beavers have been one of the most commonly   trapped furbearers. In Washington, from 1991 to 2000, an annual average of 5,289   beavers were trapped. However, the average for the past three years has dropped   to just over 1,000, due to RCW 77.15.194 .
Beavers live 5 to 10 years   in the wild.
Viewing   Beavers
Beavers are nocturnal, but   are occasionally active during the day. They do not hibernate, but are less   active during winter, spending most of their time in the lodge or   den.
Probably no animal leaves   more obvious signs of its presence than the beaver. Freshly cut trees and   shrubs, and prominent dams and lodges are sure indicators of their   activity.
Look for signs of beavers   during the day; look for the animals themselves before sunset or sunrise.   Approach a beaver site slowly and downwind. (Beavers have poor eyesight but   excellent hearing and sense of smell.) Look for a V-shaped series of ripples on   the surface of calm water. A closer view with binoculars may reveal the   nostrils, eyes, and ears of a beaver swimming.
If you startle a beaver and   it goes underwater, wait quietly in a secluded spot and chances are that it will   reemerge within one or two minutes. However, beavers are able to remain   underwater for at least 15 minutes by slowing their heart rate.
When seen in the water,   beavers are often mistaken for muskrats. Try to get a look at the tail: Beavers   have a broad, flat tail that doesn’t show behind them when swimming, whereas   muskrats have a thin tail that is either held out of the water or sways back and   forth on the water’s surface as the animal swims.
Beavers stand their ground   and should not be closely approached when cornered on land. They face the   aggressor, rear up on their hind legs, and hiss or growl loudly before lunging   forward to deliver extremely damaging bites.
Harvest   Sites
Beavers cut down trees, shrubs, and other available vegetation for   food and building materials. Large stumps are pointed, 1 to 2½ feet high, and   sometimes the tree trunk is still attached. (Fig. 4)
Tooth marks look like twin   grooves, each groove measuring 1/8 inch or more. There will be a pile of wood   chips on the ground around the base of recently felled trees. Limbs that are too   large to be hauled off are typically stripped of bark over the course of several   days. The cut on small wood usually involves a 45-degree cut typical of rodents,   but at a larger scale. Branches and twigs under ¾ inch in diameter are generally   eaten entirely.
Most harvesting is done   within 165 feet of the water’s edge. In areas with few predators, but a lean   food supply, toppled trees and other signs of feeding may be found twice that   distance from the den site. Beavers transport woody material even farther   through upstream and downstream sites.
By late fall (earlier in   cold winter areas of Washington), all family members concentrate on repairing   and building up dams and the family lodge in preparation for winter. Harvesting   is at its most intense level at this time of year.
Figure 5. The paths   beavers make where they enter and leave the water are called   slides.
(Photo by   Russell Link.)
Slides
Slides are   the paths beavers make where they enter and leave the water. They are 15 to 20   inches wide, at right angles to the shoreline, and have a slicked down or muddy   appearance (Fig. 5).
Channels
Beavers   construct channels or canal systems leading to their ponds, using them to float   food—such as small, trimmed trees—from cutting sites. Canals are also safe   travel ways for swimming instead of walking. With receding water levels during   summer, beaver activity shifts toward building and maintaining channels to   access new food supplies. Channels often look man-made, have soft, muddy   bottoms, and are filled with 15 to 25 inches of water.
Food Storage   Sites
Beavers that live in cold climates store branches of food trees and   shrubs for winter use by shoving them into the mud at the bottom of ponds or   streams near the entrance to their bank den or lodge (Fig. 2).
Droppings
Beaver   droppings are seldom found on land; those that are will commonly be found in the   early morning at the water’s edge. Individual beaver droppings are usually   cylindrical, up to 2½ inches long (sometimes shorter), and look as if they were   formed of compressed sawdust. The diameter is an indication of the animal’s   size, with 1 inch being average for adults. The color of fresh deposits is dark   brown, with lighter-colored bits of undigested wood, all turning pale with   age.
Sounds
In order to   warn each other of danger, beavers slap their tails against the water, creating   a loud splash. Sounds also include whining (noises made by kits), a breathy   greeting noise, and loud blowing when upset.
A Beaver’s   Tail
The tail of   a large beaver may be 15 inches long and 6 inches wide. It is covered with   leathery scales and sparse, coarse hairs.
The beaver’s tail has   important uses both in the water and on land. In the water, the animal uses its   flexible tail as a four-way rudder. When diving after being frightened, a beaver   loudly slaps the water with its tail; the sound warns all beavers in the   vicinity that danger is near, and perhaps serves to frighten potential   predators.
On land, the tail acts as a   prop when a beaver is sitting or standing upright. It also serves as a   counterbalance and support when a beaver is walking on its hind legs while   carrying building materials with its teeth, front legs, and paws. Contrary to   common belief, beavers do not use their tails to plaster mud on their   dams.
The tail stores fat, and   because it is nearly hairless, releases body heat, helping the beaver to   regulate its body temperature.
 
Preventing   Conflicts
Despite an appreciation for   beavers and our best intentions to live with them, beavers can become a problem   if their eating habits, and dam or den building activity, flood or damage   property.
Before beginning any beaver   control action, assess the beaver problem fairly and objectively. Are beaver   really causing damage or creating hardship requiring control action? The very   presence of beavers is often seen as a problem when, in fact, the beavers are   causing no harm. You should also determine the type of damage or problem the   animals are causing, and then match the most appropriate and cost-effective   controls to the situation.
Once you have decided to   control beaver damage, you have three control options: prevention, beaver   translocation, or lethal control.
To prevent conflicts or   remedy existing problems:
Choose and place plants   carefully.
Plant areas with Sitka spruce, elderberry, cascara, osoberry   (Indian plum), ninebark, and twinberry, because they are not the beavers’ preferred food plants. Densely plant aspen, cottonwood, willow, spirea   (hardhack), and red-twig dogwood because, once their roots are well established   the upper parts of the plants often resprout after being eaten. Planting   preferred plants away from known beaver trails will limit losses.
Note: Beavers   do use plants as construction materials that they might not eat.
Install   barriers.
The trunks of individual large trees can be loosely wrapped   with 3 foot high, galvanized welded wire fencing, hardware cloth, or multiple   layers of chicken wire (Fig. 6). Barriers can be painted to make them less   noticeable. Welded wire fencing coated with green vinyl that helps the fencing   blend in is also available.
Lengths of corrugated   plastic drainpipe can be attached around the trunks of narrow-diameter   trees.
Note: Dark-colored pipe can burn trunks in full sun; wider diameter pipe or pipe with   holes in it may prevent overheating problems.
Painting tree trunks with a   sand and paint mix (2/3 cup masonry grade sand per quart of latex paint) has   proven somewhat effective at protecting trees from beaver damage. The animals   presumably don’t like the gritty texture.
Note: Preventing access to food sources may force beavers to eat other nearby   plants, including roses and other ornamentals.
Figure 6. Various   barriers can be used to protect plants from beaver damage. All plants should be   protected to at least 3 feet above ground—or the snow line—and inspected   regularly.
(Drawings   by Jenifer Rees.)
Surround groups of trees and   shrubs with 3-foot high barriers made of galvanized, welded wire fencing or   other sturdy material (Fig. 7). (A beaver’s weight will pull down chicken wire   and similar lightweight material.) Stake the barriers to prevent beavers from   pushing them to the side or entering from underneath. An electric fence with two   hot wires suspended 8 and 12 inches off the ground is also effective at   protecting groups of plants.
Figure   7. Groups of plants can be protected from beaver damage by surrounding them   with wire fencing.
Protect large areas that   border beaver habitat by installing 4-foot high field fencing. Keep the bottom   of the fence flush to the ground, or include an 18-inch wide skirt on the beaver   side of the fence, to prevent beavers from entering underneath.
Groups of plants can be   protected from beaver damage by surrounding them with wire fencing.
Apply   repellents.
Commercial taste and odor repellents have provided mixed   results, perhaps because they need to be reapplied often, particularly in moist   weather. Taste and odor repellents are most effective when applied at the first   sign of damage, when other food is available, and during the dry season. Two   repellents that have had some success are Big Game Repellent® and Plant-skydd®.   (See “ Repellents ” in Deer for additional information.)
Control the height of   water behind a beaver dam to prevent flooding.
It may be possible to make   a small change in the depth of a beaver pond by installing a flow device at the   intended depth, extending upstream and downstream of the dam. This keeps the   rise in the water level at a minimum by using one or more plastic pipes to   continually drain the pond area (see “Flexible Leveler” below. Click to   enlarge). For leveling systems to work properly, you will have to have at least   3 feet of water in the pond area for the beaver to stay.
The flow device can be   constructed from plastic pipe measuring 4 to 12 inches in diameter, depending on   the volume of water in the stream. The end extending upstream from the dam must   be baffled to prevent beavers from damming or blocking the   pipe.
Beaver   Deceiver
Dam   removal.
It is   pointless to destroy a beaver dam because beavers (frequently many at one time)   often begin rebuilding them immediately after they are removed. Furthermore, it   may be illegal to remove a beaver dam without a permit (see “ Legal Status ”).
Live Trapping and Moving   Beavers
Live trapping and moving   beavers elsewhere (translocating) is often cost-prohibitive. Also, research has   shown that beavers seldom survive relocation, and those that do often move great   distances from the release site. However, in urban areas where lethal trapping   may be illegal or unsafe, live trapping may be the only alternative.
Hancock or Bailey   suitcase-type traps are the most commonly used live trap. (Due to the weight and   dangers associated with suitcase traps, it is recommended that only people   experienced with these traps use them.) Some success has also come from using a   4 foot long cage trap set right at the water’s edge next to the beaver slide.   Bait for live traps include freshly cut tree sprouts or branches of preferred   foods, apples, and commercial scents and lures.
If you are moving beavers to   a different site, particularly a site where other beavers are not already   present, there must be cooperation between adjacent landowners and local   wildlife officials. A cooperative evaluation of existing habitat quality and   potential adverse beaver activity is also very important. (Expect beaver to cut   and use a large number of trees for dam construction during the first year or   two.)
To help ensure the survival   of beavers, the gradient of the watercourse at the release site should be less   than 3 percent, and the site should have adequate food supply. Move beavers   during their principal dam-building period, August to October. This will allow   them time to gather a food cache, but limit their time to explore before having   to settle in for the coming of winter. It may be helpful to provide beavers with   a pickup-truck load of aspen or other trees to use as building material at or   near the release site. This may encourage the beavers to stay nearby.
See the handout Trapping Wildlife for additional information on trapping   and moving beavers.
Lethal Control
Lethal control may become   necessary when all efforts to dissuade problem beavers fail. Removing beavers is   rarely a lasting solution since survivors have larger litters, and others will   resettle good habitats.
Lethal trapping has   traditionally been the primary form of controlling beaver damage. If you feel   you need to have a beaver trapped, private individuals who work directly with   property owners on a fee basis to resolve problem beaver situations can be   hired. Call your local Fish and Wildlife office for contact information. See " Legal Status " and the handout Hiring a Wildlife Damage Control Company for additional   information. Note: State wildlife offices do not provide animal   removal services.
Shooting beaver requires   skilled marksmanship, but can be an effective control technique where it is   safe. For safety considerations, shooting is generally limited to rural   situations and is considered too hazardous in more populated areas, even if   legal.
Public Health   Concerns
Beavers can be infected with   the bacterial disease tularemia. Tularemia is fatal to animals and is   transmitted to them by ticks, biting flies, and via contaminated water. Animals   with this disease may be sluggish, unable to run when disturbed, or appear   tame.
Tularemia may be transmitted   to humans if they drink contaminated water, eat undercooked, infected meat, or   allow an open cut to contact an infected animal. The most common source of   tularemia for humans is to be cut or nicked by a knife when skinning or gutting   an infected animal. Humans can also get this disease via a tick bite, a biting   fly, ingestion of contaminated water, or by inhaling dust from soil contaminated   with the bacteria.
A human who contracts   tularemia commonly has a high temperature, headache, body ache, nausea, and   sweats. A mild case may be confused with the flu and ignored. Humans can be   easily treated with antibiotics.
Beavers are among the few   animals that regularly defecate in water, and their droppings (like those of   humans and other mammals) may cause a flu-like infection when contaminated water   is ingested. The technical name for this illness is “giardiasis.” It is more   commonly referred to as “giardia”—derived from giardia, the single-cell   protozoan that causes the disease. Another popular term, “beaver fever,” may be   a misnomer. It has never been demonstrated that the type of giardia beavers   carry causes giardiasis in humans. Giardia has been found in many animal   species, including pets, wildlife, and livestock.
Legal Status
Because beavers’ legal   status, trapping restrictions, and other information change, contact your local   wildlife office for updates.
The beaver is classified as   a furbearer ( WAC 232-12-007 ). A trapping license and open season are   required to trap or shoot a beaver.
The owner, the owner’s   immediate family, an employee, or a tenant of property may shoot or trap a   beaver on that property if a threat to crops exists ( RCW   77.36.030 ). In such cases, no special trapping permit is necessary for the   use of live traps. However, a special trapping permit is required for the use of all traps other than live traps ( RCW   77.15.192 , 77.15.194 ; WAC   232-12-142 ). There are no exceptions for emergencies and no provisions for   verbal approval. All special trapping permit applications must be in writing on   a form available from the Department of Fish and Wildlife (WDFW).
It is unlawful to release a   beaver anywhere within the state, other than on the property where it was   legally trapped, without a permit to do so ( RCW   77.15.250 ; WAC 232-12-271 ).
To remove or modify a beaver   dam you must have a Hydraulic Project Approval (HPA)—a permit issued by WDFW for   work that will use, obstruct, change, or divert the bed or flow of state waters   ( RCW   77.55 ). A permit application can be obtained from your WDFW Regional   Office or from the Hydraulic Project   Approval (HPA) web page.
In emergency situations   (when an immediate threat to property or life exists), verbal approval from WDFW   can be obtained for work necessary to solve the problem. A 24-hour hotline (360)   902-2537 is available for emergency calls during nonworking hours. During normal   hours, contact your nearest WDFW Regional   Office .
Additional   Information
Books
Hygnstrom, Scott E., et al. Prevention and Control of Wildlife Damage. Lincoln, NE: University of   Nebraska-Lincoln, Institute of Agriculture and Natural Resources, 1994.   (Available from: University of Nebraska Cooperative Extension, 202 Natural   Resources Hall, Lincoln, NE 68583-0819; phone: 402-472-2188; also see Internet   Sites below.)
Link, Russell. Landscaping for Wildlife in the Pacific Northwest. Seattle: University of   Washington Press and the Washington Department of Fish and Wildlife,   1999.
Maser, Chris. Mammals of   the Pacific Northwest: From the Coast to the High Cascades. Corvalis: Oregon   State University Press, 1998.
Muller-Schwarze, D., and   Lixing Sun. The Beaver: Natural History of a Wetland Engineer. Ithaca,   NY: Cornell University Press; and London: Comstock Publishing, 2003.
Verts, B. J., and Leslie N.   Carraway. Land Mammals of Oregon. Los Angeles: University of California   Press, 1998.
Internet Resources   (General)