Critter Corner No. 4 – The Beaver (Castor canadensis) by George Sly
Like the previously discussed muskrat and mink, the American beaver is another mammal most everyone associates with wetlands. Chances are, if you spend much time afield, you have seen evidence of the presence of beavers in the form of gnawed trees, dams, or lodges. Perhaps you have been lucky enough to see the architects of these signposts themselves. It has not always been so easy to do so. The beaver was essentially gone from Indiana by the mid-nineteenth century. Reintroduction of the species into the state began around 1935. Beavers were relatively uncommon in Indiana even into the 1970’s. I can still recall, while in graduate school in 1971, being shown a beaver dam near West Terre Haute. It was the first time that I had ever seen one. The dam struck me both as a marvel of the beaver’s industry and as a symbol of hope in the restoration of some of Indiana’s lost biota.
The beaver’s demise throughout much of its historical range was, of course, due to the luxurious fur which covers its body. Beaver fur was primarily in demand for making beaver felt hats in Europe. Beaver pelts destined for this purpose were shipped from the United States beginning in the early 1600’s. The pursuit of beavers by fur trappers is, according to numerous sources, one of the primary factors in the initial exploration of both Canada and what was to become the western Untied States. By the mid-1800’s, fashion had evolved and hats of silk rather than beaver felt became the style. With this fickle shift in human preferences, the trapping pressure directed toward the beaver suddenly declined. Even today however some fur-trapping of beavers is done. Nineteen of them were taken at GPFWA last year during the trapping season which ran from mid-November to mid-March. Beaver pelts have, most recently, been worth around fifteen dollars to the trapper.
Folks often ask why beavers so diligently work to build and maintain their dams. They do so for several reasons. By constructing dams across running waterways, beavers create a pond of some depth. These large rodents (second only to the South American capybara in size) utilize underwater entrances to their burrows and lodges. By creating a pond, beavers are thus able to enter their dens hidden from potential predators. Having deep water in which to plunge also allows surface swimming beavers to avoid danger by diving. Such an escape dive is often preceded by a wallop to the water’s surface with their broad, flat tail. The sound is much like the shot of a .22 caliber rifle and alerts other beavers to the presence of danger. Impounded water also provides the beavers with a means of floating pieces of vegetation to a lodge or dam. In the winter, the deep beaver pond may freeze near the surface but the unfrozen depths still allow the animals to move in and out of their lodges to forage for food.
In regards to food, beavers are vegetarians. Their diet consists primarily of the bark and/or twigs of trees such as cottonwood and willow. These trees are favored because they conveniently grow close to water (such plants are hydrophytic in ecological terms) and have soft wood which makes for easier gnawing. Like other rodents, beavers have one pair of enlarged incisors in the upper and lower jaws. The incisors of beavers are massive and allow them to fell a six inch cottonwood in a matter of minutes. Felled trees are then cut into sections and transported. Some may be used for lodge construction; others may go into building or repairing a dam. Many branches, and small logs, are stored on the bottom of the beaver’s pond near the lodge. The green wood is heavy, becomes waterlogged, and thus lies on the bottom. Here it is available for the beaver, during the winter especially, to simply swim out of the lodge and select a branch from its larder. This wood is usually taken back onto the dry, raised platform within the lodge where the bark is eaten. The bare branch is then taken back outside and discarded. Such bark-stripped branches littering the shore are another common sign of beaver activity in a given area. In the spring and summer other aquatic plants may be eaten. These include cattails, water lilies, sedges, and grasses. Beaver will also feed on standing corn. Just last month, in Sullivan County, I happened upon a well-defined beaver trail leading from a stream directly into a ripening corn field.
Although I have made several references to the beaver’s lodge, they do not always construct such structures. In our area, with the numerous lakes formed by strip-mining for coal, the water depth is sufficiently great as to negate the need for lodge construction. In such habitats, beavers typically burrow into the banks of the lake. However, even such bankside dens are often marked by a heavy accumulation of logs, limbs, and twigs which have had their bark eaten away. As a result the location of the den entrance, even though it is below the waterline, is quite obviously marked.
Beavers, like many other animals, tend to bear their young (called “kits”) in late spring or early summer. Litter size averages three or four offspring. Young beavers stay with their parents for a couple of years and then are driven away by the adults. Thus, a typical beaver colony consists of around six animals; these being the two adult parents and the young of the past year or two.
The behavioral repertoire of beavers is quite fascinating to those of us who enjoy natural history. However, their increasing abundance in Indiana and elsewhere has caused incidences of human-beaver conflict to escalate too. Usually the disturbances caused by beaver activity take one of two forms: cutting of trees or flooding. As mentioned, beavers usually feed on cottonwoods and willows. However, they may enter the yards of people living near lakes and fell a favorite maple or oak tree just as readily. Because of their dam-building instinct, beavers may flood croplands, lawns, or even roads. These activities may present a serious risk to both the economic and personal wellbeing of humans. Burrowing into pond dams and levees, thereby weakening them, is another common problem caused by the activities of resident beavers.
According to Department of Natural Resources statutes, landowners (or tenants) can destroy or capture nuisance beavers without a permit if the animal is discovered damaging one’s property. If this is done, your action must be reported to a conservation officer with 72 hours. Captured animals may be released elsewhere but there are restrictions. First, the animal must be released in the county of capture. Also, one must have permission from the landowner before a captured nuisance animal is released onto their property. This constraint refers not only to private property but includes land belonging to city, county, or state entities.
In spite of their potential to cause annoyances, beavers are exceedingly interesting creatures. Let us all be thankful for properties such as Goose Pond FWA. Here we are able to observe and ponder, without vexation, the fascinating behaviors of one of the most characteristic of wetland mammals.
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