Wednesday, January 17, 2018

There's Always Something New to be Learned: Beavers on the Tuolumne River

I will freely cop to the fact that I am not a particularly observant person. This is quite an admission for a guy who has been blogging for ten years about geology, the science that requires skills of observation almost like no other. Still, there it is. I lived in Stanislaus County for thirty years thinking that we have maybe twenty species of birds. In the last three years of finally paying attention to such things, I've learned that we have three hundred species, including those which utilize some of the most famous wintering grounds for migratory birds in the American West (if you want to learn more about this, check out my other blog Geotripper's California Birds)

It is along similar lines that we come to my new educational experience of the day. I've been hiking the Tuolumne River Parkway Trail since before it was completed two years ago. I've documented more than sixty bird species on my near-daily hikes as well as the presence of Red Fox, Gray Fox, River Otter, Raccoon, and a troop of feral domestic cats. And yet somehow, in all of these mini-adventures, I missed some terribly obvious evidence of one other mammal along the river. Until today, when it was made as clear as the nose in front of my face...we have beavers.
I've always been aware of fallen trees along the river, but I never thought about why. But today, the cuttings were so fresh and obvious that I had to stop and look, and I did in fact see rippling in the water nearby. I may have actually interrupted the beaver at work (although they generally work at night). I started looking around and noticed that there were plenty of other small trees that had been felled by beaver incisors.

I had to hit the books (er, Google) to find out more. It turns out that the story of beavers in California is both muddled, and complicated. For one thing, California has its own beaver subspecies, including the California Golden Beaver, Castor Canadensis subauratus. Whether the distinction is biologically valid awaits confirmation from DNA studies. There isn't a lot known about their historical distribution because as most students of history know, the beaver was eradicated over much of its range by fur trappers in the early 1800s. It was assumed by some that they never inhabited the High Sierra, although some research has indicated that they did. They may have originally ranged across the entire state except for the deserts, and even there they survive today along the Mojave and Colorado Rivers. In any case, it is thought that by the 1940s there were as few as 1,300 of them left, almost all in the Great Valley. At that time, the Department of Fish and Game decided to transplant some of the beavers into some of their former range. At this point I had another surprise: some of the transplants were taken from the Tuolumne Waterford, the very spot where I was seeing beaver sign for the first time!
Beavers can be pests, especially in places like the delta of the Sacramento/San Joaquin Rivers, where they can cause severe damage to artificial levees. On the other hand, beavers can be highly beneficial in natural (or re-established) riparian habitats. Their dams help to slow down river erosion and allow more water to percolate into the ground. They tend to cause an expansion of the riparian woodlands by widening the area where the groundwater table is close to the surface.
The other small surprise of the day was the discovery that I was not the first to notice the presence of beavers (far, far from it of course). But one of the first hits on Google was that of another frequent user of the Tuolumne Parkway Trail, a naturalist, and erstwhile geology field studies student Siera Nystrom, who has taken several of my courses. Check out some of her excellent writing at Natural History Journal. Whatever I see and get excited about, she probably has seen it first! Being observant is a powerful skill to have.
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