Beaver, Castor Canadensis, is the largest rodent in North America. Like all rodents their incisors grow constantly, requiring them to continually wear them down through gnawing. If they don't wear them down the incisors will grow and penetrate their skulls, killing them.
Biology & Damage
Beavers are herbivorous and eat a variety of leaves, shoots, aquatic herbs and the inner (cambium) layer of woody plants, which is their primary food. In Montana the willow, cottonwood and aspen are their preferred foods, but they also like maple, apple and other fruit trees, dogwood, and many ornamentals.
Beavers have been known to cut down several trees in a night.
Beavers will store food in caches under water and many of their dens and dams are also food caches.
Beavers will den either in lodges made from woody branches, mud and other debris, or dens dug into the banks of streams, lakes and ponds. Beavers build dams to maintain a constant water depth so that their dens have the safety of under water entrances. The under water food caches also provide a ready winter food supply under the ice.
The beaver habit of gnawing and killing trees, flooding through building dams or blocking culverts, and burrowing in banks causing cave-ins and erosion, will typically put beavers at odds with land owners.
Trapping
Public opinion has slowed the fur industry in recent years and lowered fur prices. As a result, the once steady harvest (trapping) of beaver is at an all time low, which has allowed beaver populations to thrive.
A regular program of trapping beavers is probably the most effective method to control beaver populations. When beavers become a nuisance you may trap them yourself or have a local trapper do it for you.
Beavers are classified as furbearers in Montana and you must have a license or damage permit to trap them. Beavers trapping season normally runs from November 1 - April 15. The Montana Trapper's Association is a good source of information on how to trap beaver and may help you to contact trappers in your area. Additionally, many of the Fish, Wildlife & Parks offices also maintain a list of trappers willing to trap nuisance wildlife.
Owners and lessees of real estate being damaged by beaver may apply for a damage permit to trap beaver under provisions of the law. Contact your local game warden for further information.
Paint with Sand
A new way to prevent beaver gnawing is to paint the tree trunks with a sand and paint mixture. Use about 8 ounces of fine sand to one quart of latex paint. Stir it often and paint trunks about four feet high. Your local paint dealer can match the color of your paint to your tree bark. The beavers do not like to gnaw on the sand mixture, and the paint will be effective for about 2 years. Latex paint will not harm the tree and it will expand with growth. However, you should avoid painting young trees less than about six feet tall.
Wire
Placing wire cages around trees are good ways to protect them. The cages can be made from hardware cloth or heavy welded wire fencing. The cages need to be put up around the trees at least 3' high but 4' is better if there may be heavy snows. Leave about 4' between the tree and the wire when you put it around the trunk. Chicken wire is not as good around large trees unless it is used in multiple layers. Chicken wire is useful to put around a group of small trees or shrubs, but you need to anchor it or the beaver will crush it down walking over it.
Fences
Fencing off groups of trees or shrubs with a low fence will protect them. Since beavers don't like being separated from the water, your fence does not have to be totally around the area, but may be on the side toward the water and/or part way up the sides. Make it a sturdy fence tight to the ground to prevent walking over or under and crushing the fence.
Electric wire
An electrified wire strung 4-6? off the ground is also an effective deterrent.
