Beaver (Castor canadensis)
Did you know?
- Beavers are the largest rodents in North America.
- Beavers were all but extinct in Illinois by the early 1930s, but since then they have made a tremendous recovery.
Description and Identification
Beavers are the largest rodent in Illinois, reaching lengths of three to three and one-half feet and weighing 25 to 60 pounds depending on the age, sex, and nutritional condition of the individual. There are records of individuals reaching 80 to 90 pounds. Their stout bodies are covered with reddish-brown to blackish fur except for the broad, dorsally flattened tail, which is covered with dark, leathery scales. The hind legs are longer than the front legs, and there are five clawed toes on each foot. The hind feet are webbed to help the beaver maneuver in water. Beavers have small eyes and ears, and the nose has valves that close when under water. The large orange-red incisors allow the beaver to chew through wood.
Beaver droppings are hard to find since they defecate in the water. Since the droppings consist of mostly wood fiber they disintegrate quickly in water.
Beavers can be found living in streams, rivers, ponds, lakes, drainage ditches, canals, and backwater embayments. Most beavers in Illinois live in burrows rather than lodges. They excavate burrows into the banks of waterways, and enter the burrow through entrances under water. The resting areas and nest of the burrow are excavated above the water line.
Where the water is deep enough and there are enough trees for building, beavers build a lodge constructed of small tree trunks, limbs and sticks that are held together with mud. The lodge may be built as part of the dam but if water levels are sufficient the beavers just build a lodge. Dams are used to control water depth to ensure that the entrances to the beaver burrow or lodge is kept underwater. It is common for beavers to stay within a half mile of an established burrow or lodge. However, males often travel farther to find mates and young may need to travel several miles to find a place to establish a territory.
Distribution and Abundance
Beavers were becoming rare in Illinois by the mid 1800s due to heavy trapping pressure. Beavers are thought to have been extirpated from in the state by the early 1900s. Reintroductions occurred in the late 1920s throughout the early 1950s. Beavers from adjacent states also likely recolonized some areas. By the mid 1950s, beavers were established in half of the counties in Illinois. Today they are common throughout the state.
Beavers begin breeding when they are three years old and are generally monogamous. Breeding occurs in late winter. Gestation is 105 to 107 days, and the young are born April to June. The female has one litter of three to five kits each year. The male leaves the burrow or lodge for the first month or two of the kits lives and the female cares for them alone. The kits are born with fur and their eyes are open. While capable of swimming when very young, the kits do not typically leave the burrow or lodge until they are about a month old. They can sometimes be seen riding around on the female's back. The kits are weaned around two months of age. The male returns around this time and the kits stay with the adults for over a year.
Beavers are herbivores (eat plant material). The types of plants they eat are dependent upon what plant species are available in the local habitat. Beavers are known to eat willow, river birch, maple, cottonwood, sweet gum, black cherry, tulip poplar, dogwood, beech, and oak. They also eat aquatic plants such as water lilies, duckweed, and cattails. On land they will consume grasses, sedges, clovers, and corn. Herbaceous plants are important sources of food during the summer months. Beavers depend on woody species for survival during the winter months. In the late summer and fall, they collect small trees and limbs and cache them underwater near the entrance to their burrow or lodge.
Beavers are nocturnal (active at night), but may be seen during the day in late summer and fall when they are busy preparing for winter. Beaver are mainly aquatic animals, coming on land only to find food or when traveling overland to find a new territory. They are well known for their ability to build dams, canals and lodges, though most in Illinois live in burrows. They typically live in colonies consisting of a male, female, the young from the previous year, and the kits of the current year. Beavers usually cut small trees less than eight inches in diameter, but are capable of cutting down trees over five feet in diameter. Since beavers do not hibernate they must cache food for the winter. When alarmed, they slap their tails against the water. If cornered they can be quite aggressive.
Beavers are relatively long-lived, with an average lifespan of seven to 10 years. Researchers have documented individuals over 20 years old. Adults have few predators besides coyotes, dogs, and people. Vehicles can be a source of mortality when beavers cross land between wetlands or in search of a new water source. Young are most often killed by flooding and minks.
Damage Prevention and Control Measures
Beaver can cause quite a bit of damage to property, including cutting down valuable trees, damaging corn fields, damming drainage ditches, and causing flooding. Once a beaver colony is established it is very difficult to control or time consuming to trap all the animals in the colony and remove the dams.
To modify a habitat to make it inhospitable to beaver typically requires major alterations to the landscape and is not usually a feasible option. Destroying the beaver dam is sometimes recommended, but this is usually ineffective since the beavers will work quickly to rebuild. Successful control of beaver damage has been reported by installing a Clemson beaver pond leveler or similar device. The leveler lowers the water level and can reduce flooding in areas where beaver are desirable.
To protect individual trees use hardware cloth or another metal barrier. The wire should be installed from the base of the tree up to the expected snow height or the height of the expected seasonal floodwaters. Fencing can be used to exclude beavers from blocking up small areas such as culverts or drainpipes, or placed along the banks of streams and ponds to restrict access to trees.
In some cases, beaver damage control requires trapping and removing the beaver colony. Keep in mind that if no habitat alteration is done, it is likely that a new colony of beavers will eventually move into the area. Beavers can be trapped using No. 330 Conibear® traps, No. 3 or larger leg-hold traps, or snares. All must be completely submerged under water to avoid taking non-target species. Live-trapping beavers is not an option, because they typically do not survive relocation. In urban areas, an animal removal permit is needed to trap beaver. In rural areas, a trapping license is needed. Nuisance wildlife control operators with experience trapping beavers can be hired to remove the beavers.
Public Health Concerns
Beavers are susceptible to tularemia, a bacterial disease that is fatal to beaver. This disease is transmittable to humans through tick bites, or contact with infected animals or contaminated water. Water sources can become contaminated by infected individuals defecating in the water or when infected animals die in the water. Symptoms in people are similar to that of the flu. Tularemia can be treated with antibiotics. Beavers can also be carriers of Giardia. Do not drink water where beavers are present.
While beaver dam building can cause humans all sorts of headaches, this behavior plays an incredibly important role in proper ecosystem functioning. By controlling water levels, beavers inadvertently create wetlands and other habitat. Besides providing themselves with a home, beavers create habitat for fish, other mammals, reptiles and amphibians, waterfowl and shorebirds. Beaver colonies and their dams should be tolerated wherever possible.
In Illinois, beaver are protected as furbearers. If beaver in an urban area are causing a problem, they may be trapped and removed if an animal removal permit is issued by an Illinois Department of Natural Resources District Wildlife Biologist. In rural areas, a trapping license is needed to harvest beaver. Beaver may be trapped from November through March. There is no limit to the number of beaver an individual with a trapping license may take during season. For full trapping regulations, visit the IDNR Licenses & Hunting website.