There's a stream that runs through the backyard of my apartment complex. There's water in it all the time, but in the rainy season after it rains it actually runs quite a lot of water, though there isn't really any flooding risk. I can see it very clearly from my deck. About a hundred feet from me there's a place where there's some rapids, and about three weeks ago two men from the county in waders were in there working, hauling out all kinds of branches and sticks which were piled up at that one point, and then using mattocks to dig out mud and dead grass. They just piled all of it up on the bank, and didn't haul it away.
Since then, every night the neighborhood dogs have been barking their heads off, and every day when I look out, more and more of the branches have moved back into the stream, in exactly the same place, all tangled together and anchored nicely. My landlady told me that it was beavers.
But my brother said he thought it was nutria. I know there are nutria around here; I've seen them. (What I saw weren't muskrats because the tails were round and they were too big.) And somehow it does really seem a bit implausible that there are beavers doing their civil engineering thing in the middle of Beaverton, Oregon, which is where I live, the city name notwithstanding.
The Wikipedia article on nutria
doesn't mention anything about dam-building, and neither does Encarta Encyclopedia. The Wikipedia article on beavers
says that beavers and humans are the only large species known that deliberately change their environment for their own benefit; it doesn't include nutria in that list. But you know how that is.
Could it be nutria? Or are beavers the only ones who do that sort of thing?