When I was a little boy, my dad would tell me all sorts of different ways to tell how harsh the winter was going to be. You could tell by the width of the black band on the wooly bear caterpillar, or how thick the mice made the linings of their nests. I never tested any of these axioms, although I did read about a study that found the middle stripe width on the caterpillar had absolutely no correlation to winter severity in Canada. But the mouse nest one intrigues me. The mice are working furiously right now, as are many of their rodent relatives, like squirrels and the largest North American rodent-the beaver.
I have been getting many calls from people who are experiencing stress due to beaver activity. Beaver dams have increased in size and number, and beavers are chewing down way more trees than they were throughout the summer. Beavers are the only animals I know of on the continent that actually change the habitat they occupy to suit their needs. If a forest does not provide enough food or shelter for a deer or a bear, these animals move to a more suitable location. Some beaver will live in a riverbank or stream bank, finding the habitat suitable.
However, if the beaver does not see enough water, it finds the outlet and constructs a dam to raise water levels to its preferred depth. In the Northwoods, typical dam construction materials are trees, rocks, and mud. Beavers use the sound of running water to cue them to leaks, and they try using whatever materials they can find to plug the holes. We give beavers a lot of credit for engineering skill, but it is probably more about trial and error and persistence.
Beavers cut down trees for food purposes as well. They eat the bark and soft tissue from the branches and eat the smaller twigs and buds. Beavers do not hibernate through the winter; they cut down as much food as they can and drag it into the water. They will pile the branches underwater near their lodge, sometimes jabbing them into the mud to hold them. Their lodge is large, with thick sturdy walls and an underwater entrance. When the lake freezes over, they will be able to swim out from their lodge, under the ice, and grab the branches from the bottom. Beavers rarely live alone; adults mate for life, and their offspring live with them for two years before heading out on their own. This means there can be a lot of beavers cutting down a lot of trees to nip off the branches to store for the winter.
So the phone calls pick up because the beavers are working like mad, impounding water to deeper depths and gathering food from lakeshore owners’ favorite trees. What can they do about it? The Department of Natural Resources does not handle beaver problems on private property; it is the responsibility of the landowner to address the problem. They can legally kill the beavers and destroy the dam. They can hire a trapper if they wish, who will remove all members of the colony. People who contact my office are given the names of reliable nuisance trappers who can provide help and advice. The advice is free; the help may come with a charge.
So, back to the idea of wildlife forecasting winter severity. Can rodents tell us what to expect for the coming winter? I have had some old timers tell me we are due for a severe winter. Most rodents don’t live ten years, how would they know? Is it the early spring, or the condition of the plants these animals rely on? Time will tell-before we know it, winter will be here, and the beavers will have to face the ice with the branches they cut. In winter, the stakes are high for wildlife.
Jeremy Holtz is a wildlife biologist with the Wisconsin DNR in Rhinelander, and writes a weekly column in the Star Journal. To contact him, call (715) 365-8999.