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Beavers are warm blooded mammals who live in cold climates. They build their homes, called lodges, in ponds which they create by damming a stream. For safety from predators they build access to the lodge in such a way that they have to go under water to get in our out. Avoiding hypothermia (excessive loss of body heat) is a real challenge for these animals.
In the winter, air temperature outside the lodge may be below zero Fahrenheit. But because the lodge is open to the water, the temperature is always close to 32 degrees F at water level. Two or three or more beavers contributing their own body heat to the water’s heat can bring the temperature inside the lodge up to a comfortable level, even on a very cold day. With their heavy fur which traps air and provides an insulation blanket, the beavers remain warm as long as they are in the lodge.
However beavers must leave the lodge and enter the water to forage for food. In the water, the fur is compressed and the air bubbles escape. Water is a good conductor of heat pulling the warmth from the beaver’s body. This means that if the beaver is in the water for more than 30 minutes, hypothermia is a real risk. Also if all of the beavers left the lodge to forage in the water at the same time, the lodge would cool down causing more of a struggle to regain heat when the beavers returned to the lodge.
This lodge heating problem is solved in a remarkable way. Most animals have fixed activity cycles when they sleep, eat, and exercise in a regular pattern which is basically the same for all members of a species. Beavers are different. In the wintertime, members of a beaver lodge will all have different eating and sleeping patterns so there is never a time when all of the beavers are out of the lodge at the same time. So when a beaver returns to the lodge after searching for food, it will return to a heated lodge maintained by the other residents. Also the lodges are generally built with two dens. One area is where the beavers actually live and stay warm. The other is a drying off room for when the beavers return home through the water entrance. It might be compared to a “mud room” which some people in cold climates add to their homes for taking off boots and coats when returning from outside.
Only intelligent planning could have created beavers to flourish in a world of hostile elements.
References-
Natural History, March 1, 2001, page 30
“beaver,” Wikipedia
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