Beaver: The benefits and the problems

Adult beaver
Adult beaver feeding. Photo: Forestry Images

Beaver (Castor canadensis) are North America’s largest rodent (they have reached weights of up to 100 pounds but adults are usually from 30 plus to just over 60 pounds) and as such have voracious appetites and are very prolific. They are found throughout the continent and occur in every county in Washington. They are semi-aquatic in that most of their life is spent in or immediately adjacent to water. They forage primarily on bark, twigs, leaves, buds, and cambium of hardwood trees and shrubs that grow in moist or wet soils and found in riparian zones. Species such as the maples, willows, cottonwood, aspen, dogwood, birch, and cascara, among others are favored foods. Conifers are not a favored food with the exception of western red cedar, although they utilize many conifers for dam and lodge building. Some aquatic plants and riparian forbs and grasses are also consumed.

Beavers form colonies usually consisting of the older adult parents, juveniles, and young of the year. The juveniles usually disperse when about two years of age and form their own colonies if suitable habitat can be found. At times, several generations and colonies will be in close proximity to each other if food and space is available.

Beavers build lodges out of sticks and mud in shallow water of ponds and lakes and on banks of slow-moving streams. They will dig bank dens or tunnels below the water line and back into the bank in deep and faster flowing streams. Dams are constructed from mud, rocks, sticks, and small logs in slow moving streams in order to flood an area within or adjacent to a food source.

Beaver typically swim to their food and even cache large piles of branches in deeper water so a food source is available in the winter when water freezes over. They are quite clumsy on land making them very susceptible to predators (coyotes, wolves, bobcats, lynx, cougars, dogs, and any other carnivore that can catch them). They will build a series of dams up and down a stream if necessary to access food sources. When food runs out they must move to better areas (if available) or succumb to starvation and predation. They are quite ephemeral but their “workings” may last for long periods on the landscape.

Abandoned beaver dams and ponds are quite common. When the dams collapse from lack of repair or are washed out from spring snowmelt the ensuing debris flow can be devastating to downstream habitats and structures. Typically, the newly exposed wet soils can be quickly recolonized by their primary riparian food resources and a new colony will eventually establish on that site. However, in more recent times the invasion of noxious weeds such as canary grass, Himalayan blackberries, and others may take over the site first, rendering it all but useless for most native wildlife.

Beaver are common in Washington and their numbers are high. They have been classified and managed as a furbearer in Washington and all other states with established harvest seasons and rules administered by the state fish and wildlife agencies for many decades.

When beavers move in

When beaver establish residency on a landowner’s property there is little middle ground—it’s either a love or hate attitude. Both viewpoints are understandable considering the aesthetic, ecological, and financial pros and cons associated with their presence. Beaver ponds established behind their dams can be excellent sources of fish and wildlife habitat while acting as silt traps and small flood control structures. Their foraging and feeding activities may result in setting succession of hardwood trees and shrubs back and invigorating sprouting and reestablishment of many early or pioneering riparian and wetland plant species when the older tree canopy is removed. On the other hand, their activities result in flooding and killing valuable timber and orchards, flooding roads, blocking culverts, bank deterioration and collapse, destruction of croplands, and even moving the riparian management zone of designated timberlands further back resulting in even greater loss of timber. These traits do not endear themselves to most landowners who rely on stewardship and harvest of timber and agricultural crops as part of their livelihood.

beaver damage
The tell-tale gnawing of a beaver is easy to spot on felled trees.

So what’s a landowner to do? You can sit back and enjoy the beaver or have some or all (if a small colony) removed to stop the damage. Licensed trappers can harvest them during the winter open season and sell the pelts (and consume the meat—it is tender and with good flavor). However, the passage of the citizens’ initiative more than a decade ago has changed the rules on this to the detriment of the landowners. Prior to the initiative several thousand beaver were harvested each season by licensed trappers and the pelts were sold to licensed fur buyers. This was done at no cost to the landowner. With the passage of the initiative, instant-kill type traps and snares were outlawed and only live traps can now be used (and then the catch must be killed by whatever means available). Live traps cost several hundred dollars each and weigh over fifty pounds. The annual legal harvest during the winter trapping season has declined to a fourth to a half of the earlier harvest levels. Most licensed trappers responding to damage complaints will charge the landowner, and the hides and meat cannot be utilized but are thrown away.

Damage control

Damage control trapping may be done at any month—even when young are in the den. Landowners experiencing damage and wanting removal must contact the Washington Department of Fish and Wildlife (WDFW) for certification of their damage and to request permits to kill beaver. That Department can also give contact information of licensed damage control trappers.

Live trapping and translocation of live beavers to other areas is seldom done. A permit and suitable release site with landowner’s or manager’s permission must be acquired. Suitable sites are those with sufficient food, water, and space that are presently unoccupied by beaver (a rare situation). Adjacent landowners do not want to inherit someone’s “problem animals”. There may be a cost associated with hiring a live trapper to do the catching and translocation with your permit. Removal of dams is seldom successful in the long term, can be expensive, and is illegal without a permit from the WDFW.

Obviously, these are not the most desirable approaches to managing a valuable resource—but when emotions guide natural resource management this can be the result. The high expense associated with timber, crop, and road loss, and with hiring a licensed trapper under permit to remove offending animals quite often leads to reducing them (in the mind of the landowner) to pest status and the ‘shoot, shovel, and shutup’ approach to management of an otherwise important public resource.

Exclusion devices

There are other approaches including screening or barricading culvert inlets and outlets to exclude beaver from damming or plugging those facilities. The openings in these barricades must be large enough to allow adult fish passage. Beaver excluders—perforated pipes passing through the dam and well into the pond— have proven successful in some applications. Plans are available for these from numerous sources. You must remember however why the beaver have built the dam (to access food in safety) and that by keeping them from increasing the size of the dam, and subsequently the size of the pond, limits or eliminates their ability to access food. This will likely force them to move elsewhere or result in their eventual starvation.

Beaver, like other species of wildlife as well as trees and crops, cannot be stockpiled—available space and resources limit the population size. The choice on management of this valuable and interesting animal resides with the landowner.