Naturalist's Notebook

A Beaver Poop Mystery

The dam is deep in a thicket and quite small. To reach it I’m forced to crab-walk into the lively creek below it. Salmonberry canes extract the small blood offering required for me to enter the world of the beaver.

Behind the dam, floodwaters stretch like a mirror in a disorienting terrain of many-stemmed bushes and branches. The reflection heightens my claustrophobia. I’m glad to see the creek pouring from several divots in the dam. A seasonal flood spreads its arms far from this dam whenever rain is prolonged, and the recent run of atmospheric rivers has filled several pastures. How high will the water go? Will it become a permanent wetland?

Crouched here I’m reminded that not all beavers are aggressive about expanding their waterways. In this case, it seems there is a good reason. To build the dam any higher, the beaver would have to extend it hundreds of feet in either direction. It has chosen the one small notch where the wetland funnels back into a creek, built its small dam, and left it at that.

In fact, I cannot find any freshly chewed sticks in the dam. Maybe the beaver truly has left.

Ah! But then I see something strange. Beaver poop! In three places atop the dam are squat greenish pellets full of wood slivers, so waterlogged they look ready to dissolve. I have never seen beaver poop in person. Lucky me! All of the literature says that beavers almost always take care of their number-two underwater. What’s going on here?

In spring and summer, beavers eat small herbs and aquatic plants. In fall and winter, when they do most of their tree-felling and dam-building, their diet is mostly leaves they have stockpiled underwater, small branches and the inner bark of trees. It is a diet heavy in cellulose, the molecule that gives strength to the cell walls of plants. We cannot digest cellulose. To us, it is dietary fiber. Only a few animals have the ability to produce the enzyme that breaks down cellulose: termites, silkworms, some earthworms, some weevil larvae, a wood-boring clam and a fish called the grass carp. No mammals.

But many mammals have a workaround. In various formats, rabbits, cows, deer and others have specialized chambers in their digestive tracts to house the bacteria that are able to break down cellulose into energy.

Because of the beaver’s diet, researchers have studied its ability to get calories from cellulose. Certain aspects of a beaver’s blood chemistry more closely resemble that of cows — which are highly efficient at processing cellulose — than that of their rodent brethren. But research so far suggests that beavers do not have any special capability in this regard, and two-thirds of the cellulose they chow down comes out the other end unchanged. This puts them far behind cows and sheep and more in league with horses and rabbits.

Interesting, sure, but anyway, why here? Out in the open. It’s unheard of. Could it be the artist’s signature? A territorial marker? Or simply floated here by the current? Have any of you seen beaver poop on a dam or elsewhere? Theories and stories appreciated. In the meantime, I’ll try to get a motion-triggered dam camera to learn more.

Speedy Meteors from a Strange Source

It is one of the best shows of the year. This year’s Geminid meteor shower is December 4-17. They peak on the 14th.

First observed from a Mississippi riverboat in 1833, the Geminids have grown in intensity since. How’s that? How can an astronomical event begin during recorded history and grow from 10-20 meteors per hour to over 120 per hour?

The Geminids are bright, speedy meteors so named because they radiate from a point within the constellation Gemini, The Twins. They are white and yellow in color. Most meteor showers are the result of Earth passing through the debris trail left by a comet. When a comet approaches the sun, its surface ice is vaporized, sending out clouds of dust and rock. When Earth barges through the debris cloud, the particles become meteors.

The Geminids are a little different. They also come from a debris trail, but this one is from a mysterious asteroid named 3200 Phaethon. The 3.6-mile-wide asteroid is weirdly blue and has a comet-like orbit, even brightening as it nears the sun. Asteroids don’t typically brighten or throw out debris. And 3200 Phaethon passes close enough to the sun that its surface temperature hits 1300 F. Any ice would have been vaporized long ago.

This year astronomers have proposed an interesting solution to the mystery of 3200 Phaethon’s debris trail. They suggest that instead of ice, it is sodium deep in the cracked asteroid that is vaporizing and fizzing. According to their models, it would not take much fizzing of sodium to dislodge bits of rock and dust from the asteroid’s weak gravitational field. This idea explains the color of the Geminid meteors. Space rocks with sodium burn orange. Only rocks from a source depleted of sodium would burn pale.

With each passing year, Earth’s orbit intersects 3200 Phaethon’s debris trail more squarely. Because the shower’s peak lasts a full 24 hours, the Geminids can be seen as soon as it gets dark, which is great for families with kids. Only one variable threatens to spoil the show. Is it too much to ask for a cloudless sky?