Return of the Beavers

2022 June 5

When we first moved to our current property a bit over 20 years ago, there was a fairly large swamp/shallow pond in the woods out back. This was a beaver pond, and it was a rich source of frogs, aquatic insects, leeches, turtles, and other such creatures. Something happened to the original set of beavers, though, and over time their dam fell into disrepair and the pond gradually drained away. As of last year, it had pretty much reverted to a simple creek about 3 or 4 feet wide.

But, probably sometime last fall, another group of beavers moved in and rebuilt the dam, and the pond is re-filling. I went down on May 19 and got some pictures, here is one of the dam from the pond side, with the excess water going over the top.

And if there was any doubt about whether this was built by beavers (and not just a case of loose debris clogging up the hole in the old dam), we can see that the beavers were bringing down fairly substantial trees right next to the dam site.

This wasn’t done by humans. That particular pattern of gnawing the base of a tree until it snaps off with the stump and the end of the log both being cut into cones is very characteristic of beavers.

They bring down the big trees so that they can get at the branches, gnawing off the bark for food and then using the sticks for dam construction.

While we can clearly see evidence of beaver activity in the area, it is less certain where the beavers are now. Normally beavers will build a “lodge” out of mud and sticks somewhere out in the middle of the pond they create, but we didn’t see anything like that. What we did see, was a hole dug into the side of a steep part of the bank that was big enough for a beaver to get into. I suspect that the beavers are living in there.

While they have filled up the pond quite a bit, there is a ways for it to go if they get more enthusiastic about it. Here is a picture of the pond from the hill next to it, that I took a couple of weeks later (which is why it is so much greener). The red line is where the creek flowed before the beavers flooded it. The ridge running across the middle of the picture and down to the right is an old railroad embankment, which makes a natural dam once the beavers plug up the hole that the people who built the railroad originally left for the creek to flow through.

That whole area is low and flat, and if the beavers build up the dam another couple of feet they will be able to flood everything up to the bottom edge of the picture, with that electrical pole standing more or less in the middle of a pond about a foot deep. This was in fact the condition things were in when we first saw the place. Unless something happens to the beavers, I fully expect them to re-flood it back to its original level within the next couple of years. Our canoe is fully capable of floating with two people in it in only about 6 inches of water, so we would then be able to canoe over a considerable expanse.

In addition to the beaver dam, we also found a couple of these peculiar holes. The opening is a couple of inches across, and it looks like something was digging in the ground and then pushing fluid, wet mud under the snow all winter.

I had seen these in swampy areas every spring for years, but didn’t have any really good ideas as to what was digging them. But then, last year, I found the body of a star-nosed mole by the road. Star-nosed moles are semi-aquatic and live in swampy areas. Given that we now have positive proof that the moles live up here, I think it is pretty good odds that this is a mole-hole. It just has a somewhat unusual appearance because the mole had to kind of extrude dirt under the snow rather than piling it up on the surface the way they normally would.

So anyway, this is an environment that undergoes constant change depending on whether the beavers are around or not. As the beavers raise the water level, the moles will move to higher ground while aquatic creatures move back in to the restored beaver pond. It will be interesting to watch which things come back first.

This next bit is unrelated, but I find it amusing. The mascot for Michigan Tech (where I work) is a Husky dog, and some years ago a bunch of donors got together and funded a giant bronze Husky statue in the middle of campus. College students being what they are, the started climbing on it, which the university administration didn’t approve of. So, they posted these signs around it:

This is more than a little reminiscent of an old Gary Larson cartoon, and I am amused that they actually found a legitimate application for a sign that was originally supposed to be a joke.

Of course, now we need to come up with a legitimate situation that would call for a “Beware of the Grass” sign, to go along with “Keep off the Dog”.

2 Responses
  1. July 16, 2022

    Amazing. Here in San Diego, the best we can do are mud wasps.

    Does the male beaver build it to attract a mate or do they pair off and build it together?

  2. July 17, 2022

    I don’t know if one beaver starts a dam and waits for another of the opposite sex to come along, or if they pair off first and find a site. I’ve been looking up literature on beaver mating behavior, but they are pretty coy on that point. They live in colonies with a number of beavers per pond, so logistically it would seem easiest to pair off from their original colony, and then look for a good site. But this seems like it would lead to inbreeding problems, so they must have a new beaver move into an established dam site at least some of the time.

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