The Beavers' Canals
When I hear mention of the canals on the surface of Mars, I always think of beavers. I can picture myself making a beaver dam or a lodge. After all what I usually see of them is out of the water. But diving in the water and digging and shaping the mud under water seems quite daunting to me. Although I should quickly add that when I saw a dry canal the beavers built below a dam, that also seemed daunting - working the hard dirt! Canals, when you really think about them, are quite an achievement, a true expression of knowledge. The beavers that make them must know where they are going.
At first glance they look simple enough. I generally see two types: canals that radiate from the pond bringing the beaver closer to trees; and canals that go down from dams to the pond below. A closer look will show the compexity. Since I observe beavers where winters are cold, these canals must be deep enough to allow passage in the winter. Just looking at a large placid beaver pond, nothing could seem easier to deepen. But the beavers created the pond, usually in an area thick with trees and bushes. Afterall that is why the beavers are there, for food. So digging a canal entails more than moving mud. Roots have to be chewed through. And when the trees begin dying and disappearing and sun floods the growing pond grasses and reeds will try to take root. Just today I walked along the shore of the Big Pond. In most places on the south shore there are thick reeds going ten yards out into the pond. But every twenty yards or so along the shore, I saw a deep, grass free canal coming up to my feet. Some had stripped willow branches at their terminus.
And most of these canals could probably accommodate two beavers passing in the night.
The series of ponds I call the Third Swamp always strike me as being in an area guaranteed to be short of water. On one side is a gentle slope with not a few small ponds and puddles in it. On the other side is a shear cliff and the ridge above generally slopes the other way into a high valley. The lack of water forced the beavers to connect the series of small ponds with canals. Two dry summers put these canals out of business for beavers. Yet twice I've been reminded of their virtues. Once I saw a Blanding's turtle using a canal. And then last winter the otters used them. The deep canal was crusted with a foot of ice and below was more or less dry. But the otters could still scoot through the canal. I pondered for awhile why the otters simply didn't scoot through the snow atop the pond as they often do. I think the reason is that they know that by following the canal they were pointed in the direction they wanted to go - up to another pond.
Another important service of canals, is that the canal of today can become the channel of tomorrow as the pond gets deeper. In Beaver Point Pond the beavers built a new lodge just beside a canal that had been built months before to gain better access to the shore. When the small ponds in the Third Swamp dried out, I walked through one that seemed to be nothing but a nexus of canals.
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