All About American Beavers

Nature's hydroengineers, American Beavers, present several challenges.
Tim Nephew
March/April 2011
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Because of a tail that serves as a rudder in water, nose and ear valves that shut when submerged, webbed feet, and an amazing lung capacity, beavers are well equipped to survive in water.
Gustav W. Verderber
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As I approached the five-wire electric fence that protects my grapevines in a remote three-acre field, I immediately knew I had a problem. The characteristic “tick, tick, tick” of the charging circuit was noticeably silent. Knowing that heavy weeds or errant brush can sometimes cause the fence to ground out, I started walking in search of the problem. As I rounded a corner of the field that borders a slough, I found the source of the short. A 20-foot poplar tree was lying across the fence pinning all five wires to the ground. Because we hadn’t experienced any severe weather recently, I was completely perplexed until I glanced at the base of tree and noticed the telltale chew marks of a beaver.

I was aware that there was a small beaver colony on my property. Occasionally I would hear the loud “slap” of a tail on water or catch the sight of a beaver swimming across the slough, but this was the first time they had caused me any problems. Higher than normal water levels were allowing the beavers access to trees near my fences and outbuildings. After spending an afternoon cutting up the fallen tree and retightening my fence, I decided to research my options for dealing with future problems and also to learn a little more about beavers.  

Beaver basics

The American Beaver is actually the largest North American rodent. It is found throughout the United States and Canada, with the exception of extreme northern Canada, the deserts of the Southwest, and most of Florida. According to the book, Beavers, by Wil Mara, the beaver’s large orange teeth are capable of chewing through a 6-inch tree in 15 minutes. With a flat, paddle-shaped tail that serves the dual purpose of acting as a rudder in the water and aiding in balance on shore, the beaver is well equipped to survive in an aquatic environment. Adding to its water-capable makeup, the beaver’s nose and ear valves shut when it submerges, and a thin membrane covers its eyes serving as a type of goggle to protect the eye from irritation. It also has lips that close behind its front teeth, enabling it to carry a branch in its mouth without drowning and protecting the beaver from swallowing any splinters of wood while gnawing through a tree. The front feet of a beaver are short and equipped with claws useful for grooming and packing mud, and the rear feet are webbed, which enhance its swimming ability. The beaver’s lung capacity is also quite amazing, allowing it to stay underwater for up to 20 minutes without resurfacing for air.

Beavers may grow to a length of 5 feet, but 3 to 31⁄2 feet is more typical. They can weigh as much as 90 pounds, with the average adult beaver typically between 40 and 50 pounds. Their coat is composed of long, coarse guard hairs over a thick undercoat and ranges in shades of brown.

Community creatures

Beavers mate when they are 2 years old. The mating season runs from November to March. Young beavers (kits or pups) are born in May or June, with an average litter of three to four. Beaver babies weigh less than a pound and have the ability to follow their mothers underwater before they are a day old. Young beavers stay with their parents for two to three years. After the first year, the parents will have another litter –
only one litter per year – and the young from the previous year will actually help care for the newborn kits. Typically, after a third year at most, beavers are “kicked” out of the colony and forced to find their own mate and territory. 

Saved from the brink

The beaver’s thick, luxurious coat or “pelt” is what led to the near extinction of the beaver population in the United States in the last century. As early as the 1500s, the beaver was trapped for its fur, which is strong, warm and has the natural ability to shed water. Hats, coats and collars made from beaver were popular and led to a worldwide demand for pelts. Much of the Westward expansion in the United States was predicated on the relentless pursuit of new and more productive beaver populations for trapping. When Europeans first came to America, it was estimated that the beaver population was anywhere from 150 million to 200 million animals. By the early 1900s, the beaver had disappeared from most of its range across the central United States. It was about this time that the public became concerned about the animal’s extinction and enacted trapping regulations, and live trapping reintroduced beavers across much of their original range. Today, the beaver population is estimated around 10 million and continues to hold stable. 

Nature’s engineers

Beavers require water to survive, so any adequate source of water such as a stream, lake or slough will provide the proper habitat. Beavers have been credited with being second only to humans in shaping their own environment. They do this through the creation of dams that stop the flow of moving water to form a larger body of water in which they build their “lodges.” Beavers create a dam by piling mud, stones and brush
beneath the water, creating a base. They then continue to pile up more brush, mud, sticks and logs. Once constructed, beavers will continue to maintain a dam for years.

A lodge is basically a pile of sticks and branches covered with mud. As the weather turns cold in the fall, the mud acts as insulation and forms a rock-hard covering over the lodge. This barrier prevents the beaver’s natural predators – wolves, lynxes and bears – from digging out the beavers inside. Sometimes stream-based beavers will forgo building lodges above ground and dig dens into the stream bank. In both cases, access to the lodge is accomplished through a water entrance just below the surface. 

The good and the bad

As stated on the Minnesota Department of Natural Resources website (www.DNR.state.mn.us), “The beaver is nature’s original water conservationist and land manager. Many biologists believe that the beaver pond supports a greater variety and abundance of wildlife than any other ecosystem in the forest. The ponds also control spring runoff, thus lessening the possibility of downstream flooding.” But the site goes on to state that, “A beaver in the right place is an ideal conservationist. In the wrong place, they become a nuisance. Wherever they become too numerous, they cause problems for people. Their dams flood farmlands, roads and timber, and their appetite for wood results in the loss of valuable fruit and shade trees.”

Damage prevention

The Minnesota Department of Resources lists some valuable tips for damage control. Here are a few:

  • Protect individual trees in your yard by placing hardware cloth cylinders at least 30 inches tall around the base of the tree. Energized fencing can protect larger areas.
  • Plant native evergreens such as common juniper that beavers do not like or other shrubs that re-grow after some beaver damage (Red Osier Dogwood, prairie or pussy willow).
  • Create a buffer strip of native vegetation suited to your location. 

Beaver removal

In most cases, the damage caused by beavers can’t be managed unless you actually remove the beavers through trapping or hunting. If you attempt to remove a dam without removing the beavers, the dam will be rebuilt immediately. In Minnesota where I live, the live relocation of beavers or any other protected wild animal is illegal, which eliminates live trapping as a viable option. Many states have trappers associations that can be helpful in either providing you with the proper information on how to remove the beavers yourself or providing the names of professional trappers willing to remove nuisance animals. Either way, if you start to have a problem with beavers on your property, you should contact your local department of natural resources so you can document your problems and perhaps receive assistance in removing the beavers.  

American Beaver facts

  • Beavers can chew through a 6-inch tree in 15 minutes.
  • A single beaver can chew down hundreds of trees a year.
  • Castoreum, a substance taken from large glands located by the beaver’s tail, is used in the making of expensive perfumes.
  • Beavers can stay underwater for up to 20 minutes.
  • One of the largest beaver dams ever documented was more than a half-mile long.
  • Beavers account for more than $20 million in damage to homes, forests and farmland each year.

Tim Nephew, a freelance writer living in northern Minnesota, manages his 80 acres for wildlife and for growing cold-climate-hardy grapes. Although the beavers on his property have caused him some extra fencing work, they have also supplied him with at least one month’s woodstove heat – and a nifty pair of insulated mittens!  


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Post a comment below.

 

John Wilkinson
2/22/2011 5:50:20 PM
The Beaver have intrigued me since I was knee high to a grasshopper. I have trapped them for both relocation and for damage control, so I'm aware of their "busy as a beaver" work ethics. They are also the only critter that is capable of creating their own habitat. I just read the article, it was very informative and accurate. However, the picture on pg. 17, is incorrect. Those are Nutria on the float not Beaver. Nutria were introduced to the U.S. from Argentina in the 60's, where they were raised on a farm for their fur. Unfortunately, they escaped and now have become very devastating in the coastal marshes in Southern states.








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