Monday, September 16, 2013

Wildlife Architecture: Building A Beaver Lodge

Beaver_lodgeAll mammals that employ the use of a shelter in winter instinctively attempt to find a place completely hidden from the view of humans for their home, except for one. When the time comes in late summer or early autumn for establishing a protective enclosure for the coming season of cold, ice and snow, only the beaver places its residence in a spot that can be readily noticed by a person passing through the area.

When hiking, canoeing, biking or driving past a stretch of quiet water, you can often see a sizeable, cone-shaped mound of sticks packed with mud jutting well above the water’s surface. This is the temporary, winter residence of a family of beaver which provides these flat-tailed creatures with shelter from the cold, and protection against their few natural enemies.

Usually during the first few weeks of autumn, after the framework of a dam has been established, a beaver family begins the process of erecting their winter den, also referred to as a lodge. The site for this structure is typically in a shallow section of water as far from the shore as possible. In a pond, or lake, where the water depth increases quickly, the beaver is often forced to situate its lodge directly on the shore. Also, in a large, fast flowing river that is impossible for this mammal to dam, the beaver digs into an elevated section of bank in order to create a den; however such an earthen lodge is avoided if any shallow shelf along the shore is available.

After a suitable site is found, the beavers start assembling a pile of sticks and limbs that have had their bark chewed off, or have no nutritional value to this bark eating creature. Coinciding with the development of the foundation of the lodge is the excavation of an underwater passageway that leads into the center of this mass of sticks. Upon reaching the surface, the beaver begins to gnaw through the sticks already in place to create a small chamber inside the mound of woody material.

Over the course of the next several weeks, an additional underwater passageway, or two are dug into the center of this pile of debris, and the size of the interior chamber is enlarged. Because of the beaver’s extremely sharp set of incisors, it takes less than a minute for an adult to cut through a two inch branch. This allows a beaver to trim the ends of sticks inside a lodge without much effort and fashion the walls and ceiling of its winter retreat to accommodate the entire family of rodents.

Throughout the autumn, more sticks are placed on top of the lodge, and coatings of mud are plastered onto the roof to fill as many of the cracks as possible. Because the beaver simply drops large handsful of sediment dredged from the bottom on top of the lodge and pushes it down, not much of this gushy material is able to make its way into the spaces and gaps directly below larger limbs. This always leaves small, yet numerous air holes on the sides of the lodge that allow for the exchange of gases providing proper ventilation to the interior living chamber.

By the end of autumn, an active beaver lodge can be five to six feet high and over twelve feet in diameter. The living chamber inside usually has a ceiling no more than two feet high with a diameter of 4 to 6 feet, depending on the number of individuals in the family. (A typical Adirondack beaver family is composed of an adult male and female, 2 to 3 yearlings, and 3 or 4 kits that were born in spring.)

It is difficult to say for certain when the family finally takes up residence in its lodge, as most of their time when the weather is warm is spent in temporary shelters that the family has developed throughout their territory. By spending only a week or two in any one shelter, the beavers are less likely to develop problems with fleas and other skin parasites that can infest the lush hide of this fur-bearer.

After living in a lodge throughout the winter, a beaver family is quick to relocate in spring. The lodge that was crafted by the family during the autumn is abandoned and may never be used again. This is why it is not unusual to see two or three different lodges scattered along the edge of a pond

that is regularly used by beavers.
The active lodge can always be identified by a fresh coat of mud placed on the upper surface of this structure. Once a lodge is abandoned, periods of heavy rains that occur throughout the summer eventually wash away this outer layer of material, leaving only the lattice of sticks and limbs in place.

The appearance of a small, shallow pond behind a beaver damn is a common sight throughout the Adirondacks, and inevitably close to the shore, there is a cone-shaped mound of sticks that is the highly visible winter residence of this remarkable mammal.

Editor’s Note: Tom Kalinowski will be presenting a lecture on Adirondack beavers at the Hadley-Luzerne Library at 7 PM on Sept. 24th. The public is welcome to attend.

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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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