The Carleton student has many strategies to survive the winter: wearing layers, drinking hot beverages and simply staying inside to name a few. Animals in the Arb, however, don’t have these same luxuries. Bernd Heinrich, in his book Winter World: The Ingenuity of Animal Survival, discusses the winter survival strategies of beavers and other animals. Most everyone has seen the characteristic piles of debris that compose beaver dens. They are built in ponds or on the banks of rivers and are constructed of tree limbs, sticks, and mud. The lodge’s thick, insulating walls keep beavers warm throughout the winter. Sometimes lodges are so well constructed that they will be refurbished and used by several generations. The entrance to the lodge is underwater and positioned several feet below the lodge cavity, creating a water lock that keeps the den dry. Beavers overwinter in groups ranging from two mates to ten-member families. This means a lodge may get very crowded, especially given that beavers are the second largest rodent (after the capybara) and often weigh 40-50 pounds. Muskrats and other rodents and small mammals have even been known to inhabit lodges with beavers.
In preparation for winter, beavers will fell trees and collect their limbs to construct one or more stick piles near their dens. Over the course of winter, they swim from their lodges to the piles, take a few sticks with them, and swim back to their lodges to eat the bark from the sticks. The beavers are trapped underneath the frozen surface of the water the entire time they do this, and often for the entire winter. They survive swimming in the ice-cold water by decreasing their heart rates and energy expenditure for as long as 15 minutes. A beaver’s winter stockpile does not contain enough calories to sustain the animal for the entire winter. To account for this calorie deficit beavers eat more in the fall to build fat stores that will be gradually used up. They also lower their internal body temperature by as much as 2℉ for the entire winter to conserve energy.
Andy Hoyt 19’, for the Cole Student Naturalists
Photo credits: On page: Brittany Johnson '18, teaser: Joanne Bouknight