Rob Rich

We have this issue, I think, as a people, just of beaver amnesia, not being able to see what the beavers created before us. And I would bet, you know, almost the entirety of us that are drinking water and flushing toilets and taking showers and all the things, our water is coming from somewhere that at some point in its history was shaped by a beaver.

Rob Rich, he, him is great.

Generally not castorologists. There was an early book in the late 1800s that had that name actually, but Generally, it's not castorology. It's either just beaver fans, beaver believers, all the things that are associated with interest and curiosity about beavers.

That's kind of the classic at the moment.

Yeah, I'm calling from northwest Montana, and I live in a valley called the Swan Valley, a little bit northeast of Missoula and south of Kalispell, up against a part of the Rocky Mountains there and below Glacier National Park. This is a special valley in a lot of ways. It's very well watered.

It has a lot of historic beaver activity and current and was also shaped by glaciers, which the beavers actively followed.

In a way, yeah. The last glaciation that covered America was about 10,000 to 12,000 years ago, I believe, as it pocked out a lot of depressional wetlands and carved the rivers in certain ways that made it really conducive to complex flows, which beavers are actively seeking out all the time. And so they find in glaciated regions of North America.

And so beavers and glaciers together are two of the major continental shapers of North America.

Yeah, so that's a great question. You know, the beaver evolution is very complex. And we actually at one time had 33 different genera of beavers and genera like the genus species binomial classification. So we had 33 different types of genus of beaver across the northern hemisphere at one time. And that is totally, at this point, winnowed down to one genus, the genus Castor.

And Castor canadensis is the North American beaver, the only one native to this continent. And Castor fiber is the beaver, the Eurasian beaver, and that is over in Europe and parts of Northern Asia as well.

About 33 million years ago, I believe, is when the beavers really started diversifying. And a lot of rodents generally, that was a really time of... rodent diversification. And so we had beavers, one that was kind of more recent times, the castoroides that lived just south of the glacial ice sheets and whatnot.

And so that was one that was about the size of a bear, almost like 175, 200 pounds in a very large beaver. We had beavers, one called paleocastor that actually dug corkscrew-like tunnels with its teeth into what we now know as the prairies of Nebraska. And so very different lifestyle.

But it wasn't until they really converged on that semi-aquatic behavior and the wood cutting and dam building behaviors. When all three of those parts converged in the Beaver, that is what drew their evolutionary success. And that's kind of the one that's persisting today.

Yeah, good question. So there's some regional variation in that. But generally, beavers in the north are a little bit larger just to have a larger body size to sustain themselves through the winter and have that energy capacity. But I would say an average size would be between 40 to 50 pounds for an adult beaver.

But they can get up to, you know, 60 to 90 pounds in some of those areas where they're quite large. And this is not sack of potato size for them at all. It's more along the size of a small dog in some ways, maybe like a border collie, but much lower to the ground, obviously shorter legs, but something along those lines when they're

Born, though, they're only about a pound or about the size of a loaf of bread, maybe. You know, that would be a good comparison. For a newborn beaver, it's about a pound.

Generally two kits, a newborn beaver is called a kit. And so generally two kits per litter, they can have up to four sometimes. The yearlings of that same monogamous pair of male and female will stay on with the family. And so you can have a combination of the two adults and then yearlings from the previous year and then newborns all in one lodge at the same time.

But by the time they reach two years old, that's typically a natural dispersal time. And so the two-year-olds will leave their natal birth area and strike out to find a new wetland that they can call their own.

That's a great question. Generally, they stay together for the entire time.

And very social and very territorial against other non-related beavers. They erect a lot of scent mounds, they're called, and they can be up to over a foot wide, a foot tall. And so there are these just heaps of dredged up vegetation and mud from the bottom of the pond or the wetland where they are.