Notes on Castor Canadensis

North American Beaver, Page Springs, Malheur National Wildlife Refuge, Oregon

North American Beaver, Page Springs, Malheur National Wildlife Refuge, Oregon

One spring evening in 1992, WC’s elkhound, Max, was barking his fool head off in his chain-link fenced run. Thinking it was yet another moose, WC went out to get the mutt. There was no moose. But suddenly something struck the other side of the base of that chain-link fence hard, rattling the length of the fence and making Max jump back.  It was a young beaver. When a young beaver is kicked out of the lodge where he was born, he migrates upstream, across the  divide, and then down a water course to new territory on the other side. WC lived near the top of a small seasonal stream. WC’s dog had interrupted this beaver’s modest migration. But here’s the thing: the beaver wasn’t backing down in the face of a frenzied elkhound, He charged the fence again and again, hissing like a steam kettle. As WC watched, the beaver ran at the fence, surprisingly fast for a waddling beaver, and at the last instant, pivoting and slamming that big tail against the fence. WC took Max and went inside.

The next morning when WC inspected his fence, that heavy fence was stretched, bowed in, from the force of the beaver’s repeated tail slaps. The metal wires were stretched out of shape from the blows.

Before the arrival of undocumented immigrants in the middle 17th Century, there were as many as 60 million beaver across North America. 250 years later, there were less than 6 million. Beaver trapping declined only because they became too scarce to profitably trap.1 A kind of near-ecological extinction.

The populations of these remarkable rodents have partially recovered. There are about 12 million now. They’ve also been introduced in environments where they shouldn’t be and, like too many invasive species, have run rampant, devastating the local environment. Tierra del Fuego comes to mind. “Busy as a beaver,” it turns out, includes breeding like rodents. Because, after all, that’s what they are.

North American Beaver, Airport Ponds, Fairbanks, Alaska

North American Beaver, Airport Ponds, Fairbanks, Alaska

All this comes to mind because WC recently read Ben Goldfarb’s Eager: The Surprising, Secret Life of Beavers and Why They Matter. Goldfarb not only does a nice job on the natural history of these big rodents; he also assembles a large collection of amazing beaver facts. A sample:

  • In North America, beavers were an ecological force. Scientists estimate there were some 234,000 square miles of beaver-created wetlands in 1700. That’s nearly half the area of Alaska. There are alpine valleys where the beaver dams are piled on top of each other a thousand feet deep.
  • When the Dutch bought Manhattan from the Lenape Indians? Manhattan was the sweetener. The real prize was the 7,246 beaver pelts that were shipped back to Europe.
  • The world’s largest beaver dam stretches 850 meters deep in the thick wilderness of northern Alberta. It was discovered after being spotted on a satellite image in 2007, It’s visible from space.
  • Beavers have a second set of lips, behind their teeth. The evolutionary necessity of that second set of lips is apparent if you reflect that the beaver makes his living dragging branches through water with his teeth.
  • The official seal of the City of New York features two beavers. Hey, the beaver pelt industry was important back then.
  • Some of the most productive farmlands in North America are former beaver ponds.

So let’s hear it for eager beavers, because WC is eager as a beaver – wait, have you ever seen a beaver that seemed “eager”? – to end this blog post.


  1. Trapping declined. It didn’t end. As many as 500,000 beavers are still trapped across North America today, mostly in Alaska and northern Canada. 

One thought on “Notes on Castor Canadensis

  1. You hit the nail on the head … in the right location they are extremely beneficial to water conservation and habitat improvement for things like Redband Rainbow, Sage Grouse and more. In the wrong place and uncontrolled they can raise havoc on native populations and habitat. In short where man has messed with the natural course of beavers we frequently have to fix our messes 🙂

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