BEAVER: (Castor canadensis)

Most beaver conflicts are associated with dam-building and flooding, or feeding damage and cutting of valuable trees. Usually beaver conflicts occur near water, where beaver lodges or bank dens are constructed. Flooding may wash out roads, damage septic systems, or kill trees in low-lying areas.

 

Health and Safety Concerns

In urban areas, beavers may become habituated to humans and may be aggressive if approached. Beavers infected with rabies, which is very uncommon, may attack people. Beavers are hosts to several ectoparasites and internal parasites, including nematodes, trematodes, and coccidia. Beavers contaminate water with Giardia lamblia, a pathogenic intestinal parasite that causes intestinal problems in humans. Trappers should avoid splashing water in their face, and carefully wash their hands before eating or smoking. Anyone who develops severe abdominal cramps or persistent diarrhea while working with beavers should consult a physician. Tularemia has been reported in beavers from Canada and the northern US. Trappers should wear rubber gloves when skinning or eviscerating beaver carcasses.Floods caused by beaver dams undermine roads and interfere with septic systems. Bank dens cause the collapse of banks along farm and shoreline properties. Falling trees pose threats to structures, power lines, and people.

 

Identification

The beaver is the largest North American rodent. Most adults weigh from 35 to 50 pounds (15.8 to 22.5 kg), with some occasionally reaching 70 to 85 pounds (31.5 to 38.3 kg). Individuals have been known to reach over 100 pounds (45 kg). The beaver is a stocky rodent adapted for aquatic environments. Many of the beaver’s features enable it to remain submerged for long periods of time. It has valvular nose and ears, and lips that close behind the four large incisor teeth. Each of the four feet have five digits, the hind feet are webbed between digits and have a split second claw on each hind foot. The front feet are small in comparison to the hind feet. The underfur is dense and generally gray in color, whereas the guard hair is long, coarse and ranging in color from yellowish brown to black, with reddish brown the most common coloration. The prominent tail is flattened dorsoventrally, scaled, and almost hairless. It is used as a prop while the beaver is sitting upright and for a rudder when swimming. Beavers also use their tail to warn others of danger by abruptly slapping the surface of the water. The beaver’s large front (incisor) teeth, bright orange on the front, grow continuously throughout its life. These incisors are beveled so that they are continuously sharpened as the beaver gnaws and chews while feeding, girdling, and cutting trees. The only way to externally distinguish the sex of a beaver, unless the female is lactating, is to feel for the presence of a baculum (a bone in the penis) in males and its absence in females.

 

Range

Beavers are found throughout North America, except for the arctic tundra, most of peninsular Florida, and the southwestern desert areas. The species may be locally abundant wherever aquatic habitats are found.

 

Habitat

Beaver habitat is almost anywhere there is a year-round source of water, such as streams, lakes, farm ponds, swamps, wetland areas, roadside ditches, drainage ditches, canals, mine pits, oxbows, railroad rights-of-way, drains from sewage disposal ponds, and below natural springs or artesian wells. Beavers build dams to modify the environment more to their liking.Dam building is often stimulated by running water. The length or height of a dam generally depends upon what is necessary to slow the flow of water and create a pond. In areas of flat topography, the dam may not be over 36 inches (0.9 m) high but as much as ¼ miles (0.4 km) long. In hilly or mountainous country, the dam may be 10 feet (3 m) high and only 50 feet (15 m) long. Beavers are adaptable and will use whatever materials are available to construct dams — fencing materials, bridge planking, crossties, rocks, wire, and other metal, wood, and fiber materials. Therefore, about the only available aquatic habitat beavers avoid are those systems lacking acceptable foods, lodge or denning sites, or a suitable dam site. Some of the surrounding timber is cut down or girdled by beavers to form dams. Subsequent flooding of growing timber causes it to die, and aquatic vegetation soon begins growing. Other pioneer species (for example, willow, sweetgum, and buttonbush) soon grow around the edges of the flooded area, adding to the available food supply. The beaver thus helps create its own habitat.

 

Food Habits

Beavers prefer certain trees and woody species, such as aspen, cottonwood, willow, sweetgum, blackgum, black cherry, tulip poplar, and pine, depending on availability. However, they can and will eat the leaves, twigs, and bark of most species of woody plants that grow near the water, as well as a wide variety of herbaceous and aquatic plants. Beavers often travel 100 yards (90 m) or more from a pond or stream to get to corn fields, soybean fields, and other growing crops, where they cut the plants off at ground level and drag them back to the water. They eat parts of these plants and often use the remainder as construction material in the dam. The size and species of trees the beaver cuts is highly variable — from a 1-inch (2.5-cm) diameter at breast height (DBH) softwood to a 6-foot (1.8-m) DBH hardwood. In some areas beavers usually cut down trees up to about 10 inches (25 cm) DBH and merely girdle or partially cut larger ones, although they often cut down much larger trees. Some beavers seem to like to girdle large pines and sweetgums. They like the gum or storax that seeps out of the girdled area of sweetgum and other species.

 

General Biology, Reproduction, and Behavior

Beavers are active for approximately 12 hours each night except on the coldest of winter nights. The phrase “busy as a beaver” is appropriate. It is not uncommon, however, to see beavers during daylight hours, particularly in larger reservoirs.Beavers are generally monogamous; copulation may take place either in the water or in the lodge or bank den. After a gestation period of about 128 days, the female beaver generally gives birth to 3 or 4 kittens between March and June, and nurses them for 6 weeks to 3 months. The kittens are born fully furred with their eyes partially opened and incisors erupted through the gums. They generally become sexually mature by the age of 1 ½ years.Beaver communicate by vocalizations, posture, tail slapping, and scent posts or mud mounds placed around the bank and dam. The beaver’s castor glands secrete a substance that is deposited on mud mounds to mark territorial boundaries. These scent posts are found more frequently at certain seasons, but are found year round in active ponds.Beavers have a relatively long life span, with individuals known to have lived to 21 years. Most, however, do not live beyond 10 years. The beaver is unparalleled at dam building and can build dams on fast-moving streams as well as slow-moving ones. They also build lodges and bank dens, depending on the available habitat. All lodges and bank dens have at least two entrances and may have four or more.The lodge or bank den is used primarily for raising young, sleeping, and food storage during severe weather. In Missouri beavers are most likely to dwell in bank dens rather that constructing lodges.An important factor about beavers is their territoriality. A colony generally consists of four to eight related beavers, who resist additions or outsiders to the colony or the pond. Young beavers are commonly displaced from the colony shortly after they become sexually mature, at about 2 years old. They often move to another area to begin a new pond and colony. However, some become solitary hermits inhabiting old abandoned ponds or farm ponds if available.In Missouri beavers have only a few natural predators aside from humans, including coyotes, bobcats, river otters, and mink, who prey on young kittens. In other areas, bears, mountain lions, wolves, and wolverines may prey on beavers.Beavers are hosts for several ectoparasites and internal parasites including nematodes, trematodes, and coccidians. Giardia lamblia is a pathogenic intestinal parasite transmitted by beavers, which has caused human health problems in water supply systems. The Centers for Disease Control have recorded at least 41 outbreaks of waterborne Giardiasis, affecting more than 15,000 people.

 

Damage and Damage Identification

The habitat modification by beavers, caused primarily by dam building, is often beneficial to fish, furbearers, reptiles, amphibians, waterfowl, and shorebirds. However, when this modification comes in conflict with human objectives, the impact of damage may far outweigh the benefits.Most of the damage caused by beavers is a result of dam building, bank burrowing, tree cutting, or flooding. Some southeastern states where beaver damage is extensive have estimated the cost at $3 million to $5 million dollars annually for timber loss; crop losses; roads, dwellings, and flooded property; and other damage. In some states, tracts of bottomland hardwood timber up to several thousand acres (ha) in size may be lost because of beaver.Some unusual cases observed include state highways flooded because of beaver ponds, reservoir dams destroyed by bank den burrows collapsing, and train derailments caused by continued flooding and burrowing.Housing developments have been threatened by beaver dam flooding, and thousands of acres (ha) of cropland and young pine plantations have been flooded by beaver dams. Road ditches, drain pipes, and culverts have been stopped up so badly that they had to be dynamited out and replaced. Some bridges have been destroyed because of beaver dam-building activity. In addition, beavers threaten human health by contaminating water supplies with Giardia. Identifying beaver damage generally is not difficult. Signs include dams; dammed-up culverts, bridges, or drain pipes resulting in flooded lands, timber, roads, and crops; cut-down or girdled trees and crops; lodges and burrows in ponds, reservoir levees, and dams. In large watersheds, it may be difficult to locate bank dens. However, the limbs, cuttings, and debris around such areas as well as dams along tributaries usually help pinpoint the area.

 

Damage Prevention and Control Methods

In Missouri, beavers are classified as furbearers and protected by regulated trapping seasons. However, damage-causing beavers may be controlled to prevent further damage. The most effective control method for beavers is trapping. Our technicians will help you determine the best options for your situation. The most important point is that damage control should begin as soon as it is evident that a beaver problem exists or appears likely to develop. Once beaver colonies become well established over a large contiguous area, achieving control is difficult and costly. One of the most difficult situations arises when an adjacent landowner will not allow the control of beavers on their property. In this situation, one can expect periodic reinvasions of beavers and continual problems with beaver damage, even if all beavers are removed from the property where control is practiced.

• Exclusion - It is almost impossible as well as cost prohibitive to exclude beavers from ponds, lakes, or impoundments. If the primary reason for fencing is to exclude beavers, fencing of large areas is not practical. Fencing of culverts, drain pipes, or other structures can sometimes prevent damage, but fencing can also promote damage, since it provides beavers with construction material for dams. Protect valuable trees adjacent to waterways by encircling them with hardware cloth, woven wire, or other metal barriers. Construction of concrete spillways or other permanent structures may reduce the impact of beavers.

• Habitat Modification - Because beavers usually alter or modify their aquatic habitat so extensively over a period of time, most practices generally thought of as cultural have little impact on beavers.Where feasible, eliminate food, trees, and woody vegetation that is adjacent to beaver habitat. Continual destruction of dams and removal of dam construction materials daily will (depending on availability of construction materials) sometimes cause a colony or individual beavers to move to another site. They might, however, be even more troublesome at the new location.The use of a three-log drain or a structural device such as wire mesh culverts or T-culvert guards will occasionally cause beavers to move to other areas. They all prevent beavers from controlling water levels. However, once beavers have become abundant in a watershed or in a large contiguous area, periodic reinvasions of suitable habitat can be expected to occur. Three-log drains have had varying degrees of success in controlling water levels in beaver impoundments, especially if the beaver can detect the sound of falling water or current flow. All of these devices will stimulate the beavers to quickly plug the source of water drainage.A new device for controlling beaver impoundments and keeping blocked culverts open is the Clemson beaver pond leveler. It has proven effective in allowing continual water flow in previously blocked culverts/drains and facilitating the manipulation of water levels in beaver ponds for moist-soil management for waterfowl and other environmental or aesthetic purposes. The device consists of a perforated PVC pipe that is encased in heavy gauge hog wire. This part is placed upstream of the dam or blocked culvert, in the main run or deepest part of the stream. It is connected to non-perforated sections of PVC pipe which are run through the dam or culvert to a water control structure downstream. It is effective because the beavers cannot detect the sound of falling or flowing water as the pond or culvert drains; therefore, they do not try to plug the pipe. The Clemson beaver pond leveler works best in relatively flat terrain where large volumes of water from watersheds in steep terrain are not a problem.

• Trapping - The use of traps in most situations where beavers are causing damage is the most effective, practical, and environmentally safe method of control.The effectiveness of any type of trap for beaver control is dependent on the trapper’s knowledge of beaver habits, food preferences, ability to read beaver signs, use of the proper trap, and trap placement. A good trapper with a dozen traps can generally trap all the beavers in a given pond (behind one dam) in a week of trap nights. Obviously in a large watershed with several colonies, more trapping effort will be required.

• Shooting - Beavers are most active from late afternoon to shortly after daybreak, depending on the time of year. They usually retire to a lodge or bank den for the day. In Missouri night shooting is not permitted, making shooting a poor control method. In most situations local authorities have regulations and restrictions regarding the use of firearms. Although this method is impractical, beaver can be shot, where allowed, if the opportunity arises. Caution must be exercised, because bullets will ricochet off water and ricocheting bullets are unpredictable and dangerous. Most shooting is done with a shotgun at close range at night. Shooting alone is generally not effective in eliminating all beaver damage in an area. It can, however, be used to quickly reduce a population.

• Other Methods - Because of the frustration and damage beavers have caused landowners, almost every control method imaginable has been tried. These range from dynamiting lodges during midday to using snag-type fish hooks in front of dams, road culverts, and drain pipes. Such methods rarely solve a damage problem, although they may kill a few beavers and non-target species. They are not recommended by responsible wildlife professionals. One method used occasionally along streams prone to flooding is shooting beavers that have been flooded out of lodges and bank dens. This method is often dangerous and rarely solves a damage problem.

 

Economics of Damage and Control

The economics of beaver damage is somewhat dependent on the extent of the damage before it has been discovered. Some beaver damage problems are intensive, such as damage caused by one or two beavers in a new pond, damming or stopping up a culvert or drain pipe, flooding roads, or crops. Other problems are extensive, such as several beaver colonies in a flatland area, responsible for the flooding of several hundred acres of marketable timber that will die unless the water is removed quickly. Generally speaking, if a culvert or drain pipe can be unstopped, a knowledgeable trapper can remove one or two beavers in a night or two and eliminate further damage in an intensive damage situation. However, an extensive situation may require a concentrated effort with several trappers, dynamiting or pulling dams, and a month or more of trapping to get the water off the timber and reduce further timber losses.Economic damage is estimated to have exceeded $40 billion in the Southeastern United States during a recent 40-year period. This would include all damage to crops, forests, roads, pastures, and other rural and urban properties. Economically, one must assess the situation and weigh the tradeoffs: the potential loss of thousands of board feet of timber and years of regeneration versus the cost of trapping. The cost of a couple of nights’ trapping and a half-day of labor to clear the culverts is much less than the cost of rebuilding a washed-out road or losing flooded crops or timber.The most important point is that damage control should begin as soon as it is evident that a beaver problem exists or appears likely to develop. Once beaver colonies become well established over a large contiguous area, achieving control is difficult and costly. One of the most difficult situations arises when an adjacent landowner will not allow the control of beavers on their property. In this situation, one can expect periodic reinvasions of beavers and continual problems with beaver damage, even if all beavers are removed from the property where control is practiced.Although benefits of beavers and beaver ponds are not covered in depth here, there are a number. Aside from creating fish, waterfowl, furbearer, shorebird, reptile, and amphibian habitat, the beaver in many areas is an important fur resource, as well as a food resource. For those who have not yet tried it, beaver meat is excellent table fare if properly prepared, and it can be used whether the pelts are worth skinning or not. It also makes good bait for trapping large predators. Proper precautions, such as wearing rubber gloves, should be taken when skinning or eviscerating beaver carcasses, to avoid contracting transmissible diseases such as tuleremia.