Beavers Repairing and Reinforcing Lodges and Dams
Late October and early November is the busiest time of year for beavers. Their entire winter’s food supply must be cut, gathered, transported and piled next to their lodge so that they will have access to it under the ice. Mud, sticks, wads of grass and stones are collected to reinforce the lodge’s thick walls against the cold as well as coyotes and other predators. And dams, the structures which create ponds, must be patched and strengthened to withstand the rigors of winter.
The importance of maintaining a dam in good condition cannot be overstated, for without it, the pond would cease to exist, and no pond means no beavers. As Dietland Muller-Schwarze and Lixing Sun state in the Beaver, a beaver pond is a “highway, canal, escape route, hiding place, vegetable garden, food storage facility, refrigerator/freezer, water storage tank, bathtub, swimming pool and water toilet.” (They defecate only in water.)
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Beavers & Pounding Headaches
Beavers will do their very best to secure fresh cambium as long as they have access to land. Even when thin ice starts to form, they are undeterred. You can hear them as they use the top of their heads to bump up against the ice in order to break through and create a pathway to shore. Thanks to Kay Shumway, a beloved friend, I had ten good years of observing this behavior every late fall/early winter. Eventually the thickness of the ice confined the beavers to their lodge and the surrounding water beneath the ice, but until that happened you could count on seeing the sun glinting off the ice shards that inevitably ended up on top of the beavers’ heads.
Beavers Actively Winterizing Lodges
There are two noticeable differences in the appearance of an active beaver lodge in the fall as opposed to the summer. One is the presence of a growing pile of freshly-cut branches adjacent to the lodge. These branches provide resident beavers with the nutrition they will need during the winter months when herbaceous plants are neither available nor accessible.
The second change noticeable in a fall lodge is the presence of massive amounts of mud. Branches are often placed on top of this layer of mud, so you have to observe the lodge before that happens in order to see the extent of the mud layer. It provides protection from harsh winter winds which would significantly lower the temperature inside the lodge. Together, a blanket of snow and a layer of mud serve as excellent insulation for beavers living in the lodge.
In the Northeast, where the temperature often dips into the single digits or lower in the winter, the interior of an active beaver lodge maintains a relatively stable 33° F. – 35° F., roughly the temperature of the water, thanks to the ingenuity of these rodent architects.
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What Determines The Internal Air Temperature Of An Active Beaver Lodge In Winter?
Regardless of the outside temperature, the interior of occupied beaver lodges has a fairly stable temperature of about 32°F. This is due to several factors, one of which is insulation. Beavers spend much of the fall collecting and stuffing mud into the cracks between the branches that provide a framework for their lodge (leaving a mud-free air vent at the top of the lodge). This mud as well as any snowfall that occurs during the winter help keep out the cold and retain the warmth that the resident beavers’ bodies radiate.
A comparison of the (cooler) interior temperature of bank dens and that of open-water lodges confirms that the temperature of the substrate underlying a lodge also contributes to the air temperature of the chamber.
Lastly, heat produced by beavers raises the temperature of a lodge above that derived from the lodge substrate.
(Photo: beaver lodge on a morning cold enough to show “beaver breath” escaping through the air vent that runs up through the center of the lodge to its peak. Thanks to Kay Shumway for photo op.)
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