Friday, March 2, 2012

Beaver Dam in Late Winter

March 1, 2012

The fact that a beaver pond is hosting an active beaver colony is no secret.  All it takes is a look at the dam and you’d see an accumulation of freshly peeled sticks. With a large beaver colony, there will be a lot of these. They give the dam a mottled appearance –with blond sticks on top of dark brown mud. Though placement of the sticks looks arbitrary, most of the branches have been set in just the right spot –according to some beaver’s discerning eye. In other times of year, you probably wouldn’t see such a large number of the peeled sticks, but in winter, the beavers are more confined; they eat most of their food in the home pond where their winter food supply is stored, and so the wood left over from their meals builds up and is dealt with on location. Luckily for them the byproduct from their meals turns out to be one of their main construction materials –talk about efficient recycling!
The dam itself is an amazing structure and no 2 beaver dams are exactly alike. Longer dams run a serpentine course, bending into and away from the pond’s center at irregular intervals. Beavers don’t usually do straight lines –even though one might think that it would save them a lot of work and materials if they did. But, by bending a dam in toward the pond –especially in a place that carries a strong current, they are able to alleviate some of the stress on the dam created by the water pressure.

The dam at our main beaver pond is up to 6 feet high at its tallest point and at its widest point –beneath the water, it’s probably greater than 12 feet wide. The dam is primarily made of mud and woody branches, but there is also a considerable amount of stone contained in its interior. These stones are usually the size of small field stones or smaller, and they are most obvious on the very top of the dam where they share space with the peeled branches. It’s tempting to think the beavers are concentrating on aesthetics here, with their use of “facing stones” neatly laid into the dark mud and interspersed among the straw colored sticks. Certainly it isn’t obvious how these particular stones and sticks serve any practical function. Just maybe this is the beavers’ way of decorating their front porch.

Over the years, I’ve found some curious items on top of the dam –things that maybe the beavers thought were worthy of display. One was an antique beer can that they likely dredged up from the bottom of the pond. I doubt that the beavers drank the contents –it wasn’t their brand for one thing. Old shards of stoneware pottery have also shown up on the dam; the shards probably eroded out of the stream bank at the site of some forgotten farm dump (A surprisingly large number of dumping sites can be found around old farms). These dredged up artifacts were apparently deemed worthy of special attention by the beavers –enough so to be carefully placed on top of the dam –as opposed to being unceremoniously shoved into the mass of the dam’s structure and plastered over with mud.
Beaver dams are incredibly leaky structures, so they require frequent maintenance by beavers or else the water level of the ponds will drop. Come spring, additional material will be added to the dam and mud will be plastered over the top, so what is now on the top of the dam is destined to become part of its interior.

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