Different animals have different strategies for surviving the winter.
In this week’s Wildlife Matters, the Masked Biologist gives us a glimpse under the ice to examine the habits of the beaver.
I sometimes ask my family members what I should write about; after writing hundreds of articles and episodes like these, I might struggle for a fresh new idea from time to time. One of my kids thought I should write about beavers in winter. This arose from a disagreement he had with a classmate about the diet and habits of beavers in prior weeks.
Every fall, beaver activity ramps up across the Northwoods. Beavers work year-round tending to their dams and lodges, but especially so when they start to prepare for surviving the winter. Their food is live plant matter, basically, and includes the tender living layers of inner tree bark, small twigs, shoots and buds. Beavers do not hibernate in winter, so they need to have food available, but most living plants are dormant, trees are not moving sap through their bark, and frankly snow cover makes it difficult for beavers to move around. So, the beaver has an interesting solution, although it may not seem that novel to us—it stores food for the winter.
Beavers always live in a residence with an underwater entrance, either in a burrow excavated in a stream bank or in a lodge it constructs itself from branches. The underwater entrance allows it to move in and out of its residence undetected, but in the winter when the ice forms it can really restrict movement beyond the water’s surface. Every fall, then, the beaver colony members chip in and start storing up food for the winter. They drop numerous trees and snip off the branches, dragging them down well-worn paths to the water’s edge. They swim to the deepest part of a small pond or an area near the lodge with a soft mud bottom in larger lakes and plunge the thicker part of the stick into the mud. Sometimes you can see the top of a food cache emerging from the water’s surface later in fall in smaller ponds, or if you try to pull water levels down by breaching their dam. These submerged sticks will stay green and limber submerged in the cool water. As the winter ice forms, the water surface is sealed up, and beavers become much less active, moving much more slowly and spending most of their time in their lodge. When they need food, they simply swim out and excavate a branch, bringing it into their lodge for family members to dine upon. They eat the smallest twigs and buds entirely, but as they move down to the thicker parts of branches, they start to eat only the bark and leave the hard undigestible heart wood behind. The remains of their meal is then extracted from the lodge, to be used later to add onto the outer layers of the lodge itself or maybe the dam if they are large enough.
During the winter, the greatest peril a lodge might face could be if the water level drops too low. This could allow the water to freeze low enough to trap beavers in their lodge, or drop the water level low enough to freeze up their food cache. This means that the beavers need to be able to patrol their pond, and if necessary conduct repairs to the dam. There is usually a hole in the ice near the dam that the beavers work to keep open in case they need to tend it. Beavers are considered an excellent alternate food source for wolves, which have been documented staking out these beaver holes hoping to snag a high fat, high protein meal.
The beavers take advantage of this sluggish and encapsulated winter period to breed in late winter. This allows them to give birth and nurse when there is less work to do, and the young are weaned and ready to munch as spring arrives and they are able to leave the lodge and find green vegetation. They can produce two to four offspring, depending on the year, and the young often stay with the parents for over a year which means there can be as many as eight beavers in a single colony sharing living space in that lodge all winter long.
Striving to make new things familiar and familiar things new, this is the masked biologist coming to you from the heart of Wisconsin’s great Northwoods.