Monday, January 23, 2012

Wildlife: Inside A Beaver Lodge in Winter

The lack of a deep covering of snow this season has been a benefit to some forms of wildlife, and a detriment to others. Yet for the beaver (Castor canadensis), the limited amount of snow on the ground has had little impact on this rodent’s winter routine.

Throughout the autumn, when the water around its primary lodge remains open, the beaver scours the shore near and far in search of those select woody plants on which it relies for food. These items are severed at their base and floated to the area just outside the main entrance to the family’s winter shelter and then pushed underwater as deep as possible.
Like many rodents, the beaver assembles a sizeable cache of food for use in winter when travel conditions become limited. Additionally, this rather rotund mammal develops deposits of fat that help to insulate it against the cold and can be used to fuel its internal energy needs.

As ice forms along the shore and around its lodge, the beaver starts to curtail its nightly foraging excursions and develops a more sedentary lifestyle. The stick and twig lodge that was packed with a coat of mud and sediment from the bottom of the pond during early to mid autumn now becomes the family’s full time home. Prior to mid-autumn, the beaver is known to rest during the day in a number of temporary shelters located throughout this creature’s territory. This allows its winter lodge to remain relatively free from the skin parasites that can eventually infest the sleeping quarters with nearly continuous occupancy.

By packing mud into the many cracks and crevices that exist between the stick and branch framework of this familiar, cone-shaped structure, the beaver helps seal out cold air and keeps in the warmth that the individuals in the family radiate to this small enclosure.
Yet, regardless of how much gushy material a beaver dredges up from the bottom of its aquatic domain, and deposits on the roof and walls of its lodge, there are always enough small holes and spaces just under sizeable limbs in the sides to allow some fresh air to enter the chamber and the carbon dioxide inside to escape. Even following a period of freezing rain, when a solid layer of ice forms on the roof, the naturally occurring holes on the sides that lead to the interior still provide for adequate ventilation of this shelter.

A substantial blanket of snow, such as the one the region experienced late last February and March, does create a thermal insulating layer over the lodge; yet several experiments have shown that the interior still remains very near 32 degrees. When snow is lacking and the outside air falls well below zero, the temperature inside may drop to a degree or two below freezing. As the sun shines on the southern walls of the dark, earthen lodge during an outbreak of arctic air, it effectively absorbs this solar energy, and the temperature inside returns to the freezing point and stays there until well after sunset.

As a general rule, the occupants periodically plunge into the icy water of the entrance and swim to their food cache to grab something to eat. During the early part of winter, many of the deeper limbs and twigs that were stored are easily accessed from the large pile assembled there. As the winter progresses and the layer of ice overhead expands downward into the pile of stored brush, the beaver must free most food items from the ice above. Because the beaver has the ability to gnaw while it is underwater, it only takes a few bites with its set of sharp incisors to sever those parts embedded in the ice and haul the remaining piece back into the lodge.

Because water is far more dense than air, heat is lost from this mammal at a much faster rate when it is immersed in water than when it is sitting on a dry shelf inside its lodge. This more rapid cooling prevents the beaver from entering the water more than it has to in order to expel its wastes and grab a quick meal.

During periods of unseasonably cold weather, the occupants of a lodge may remain inside in a very quiet state, huddled together in order to limit the cooling effect that occurs when an individual plunges into the water and reenters the lodge having lost some of its body heat.
The winter routine of a beaver is far different from that which this animal experienced just a few months earlier as it was preparing for this season of cold and ice. The reputation of the beaver as an energetic and highly productive creature comes from its autumn activities. For the present time, this rodent leads a life that is more reminiscent of a sloth.

Illustration courtesy Wikipedia.


Tom Kalinowski

Tom Kalinowski is an avid outdoor enthusiast who taught field biology and ecology at Saranac Lake High School for 33 years. He has written numerous articles on natural history for Adirondack Life, The Conservationist, and Adirondack Explorer magazines and a weekly nature column for the Lake Placid News. In addition, Tom’s books, An Adirondack Almanac, and his most recent work entitled Adirondack Nature Notes, focuses on various events that occur among the region’s flora and fauna during very specific times of the calendar year. He also spends time photographing wildlife. Tom’s pictures have appeared in various publications across the New York State.




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