Valley City Times-Record
More than just a gnawing, humble beaver
With winter ramping up, once again, spring seems to be forever away. But never fear, it is right around the corner as March 20 marks the first official day of spring for 2023.
Soon the sparrows that overwinter will be singing- and we can hear it now that the wind isn’t howling quite so loudly- and the sunshine is warm on our upturned faces.
And underground, where the mammals mostly muster during the cold winter, creatures are beginning to stir. A single badger has been spotted, digging down through the snow after some food. The smell of a skunk, while not quite like a rose, is a harbinger of warmer weather and quite possibly spring. After all, it is midway through February.
Although spring is coming, sweaters and warm socks are still king of the wardrobe. We need layers of warm clothes underneath a wind-shedding jacket to stay warm in our northern clime. But many creatures wear their warm coats exclusively, and the careful design of them is most ingenious.
Take the beaver, for example. The only member of Castoridae, its family, in North America, the beaver is quite interesting. Castor canadensis is its scientific name, which stems from the two pairs of castor sacs that produce strong pheromones, which beavers then deposit on logs and mud piles to mark their territory, according to Mammalogy by Feldhamer et. al. (3rd edition).
The truly intriguing part of those castor sacs is that they have quite the history of being used… in food. Usually, glandular secretions are very strong and actually quite unpleasant. But castoreum, as the secretion from a beaver’s castor glands is called, is said to be reminiscent of vanilla. And actually, when the beaver-fur mania was at its height, castoreum was said to be mixed in with artificial vanilla to add some extra flavor. Furthermore, castoreum was a highly prized ingredient in perfumes.
Today, castoreum gets far less attention, and beaver populations continue to climb as a result.
Beaver fur is surprisingly soft, and though it is thick, it is not the fur itself that keeps the animal warm. The fur traps a layer of air between the hair and its skin, which helps the beaver stay warm and also aids in buoyancy.
Buoyancy is a good characteristic to have when a mammal spends much of its time in or near the water, as do beavers. Besides their fur, beavers can close off their nostrils and ears which Feldhamer’s Mammalogy calls ‘valvular,’ and they also have webbed hind feet.
The tail of a beaver is another feat of engineering: As a large, flat appendage, the tail is just begging to freeze in our winter weather, right? Wrong.
A beaver’s tail is not like the palm of a hand- and those of us going gloveless in the winter know how quickly frostbite can set in. Rather, a beaver’s tail is more like a duck’s foot. Duck feet have webbing between the toes, but that webbing is very thin, and if held up to the light one can nearly see through it. Beaver tails are thicker than a duck’s foot, but the mechanism for keeping them from freezing is the same.
The rete mirabile, or wonderful net.
Our circulatory system is miraculous enough- oxygenated blood goes from the lungs to the heart and is then pumped all over the body, and when it is depleted of oxygen, it goes back to the lungs to be reoxygenated and the cycle begins all over again. Tracing the flow of blood around the body, even on a humble diagram, is incredible to behold.
But the rete mirabile adds another layer of complexity to the already complex circulatory system. Now, instead of the warm blood from the body’s trunk making its rounds all over the body and bringing with it warmth along with oxygen, it leaves the warmth in the trunk.
Have you ever held your hand above something very hot or very cold without touching it and still felt the heat or the cold?
The fine tracery of networked blood vessels in the rete mirabile are like your hand and the hot or cold object. In the cold and hot objects (which in real life would be the beaver’s tail and the beaver’s body), blood is flowing in opposite directions, and through a truly miraculous feat, the warmth mostly remains in the body’s trunk while the oxygen is given to the tail.
That’s why a beaver’s large, flat tail and a duck’s wide, flat foot doesn’t freeze.
Finding signs of a beaver isn’t a difficult aim. The picturesque tree trunks that have been whittled to a point are a reality instead of just a movie portrayal, and where beavers live, large areas of trees are cut in that fashion. Some parts of those logs are eaten; beavers like the bark, leaves, roots, and cambium. Cambium is the layer directly under the bark that is responsible for growing the tree thicker and adding to xylem and phloem on either side of itself, and are sort of like stem cells. Cells in the cambium are not specialized yet (like into a certain type of cell), and that’s why they can become both xylem and phloem cells.
Beavers take the rest of the logs they fell and make them into a dam on a body of moving water like a stream or small river. The goal in such an undertaking is to create a pond, to which the busy little critter then adds a lodge.
Inside a beaver lodge, which is a log cabin using mud chinking, the beavers living there keep the temperature at or above freezing, even in temperatures of negative 41 degrees fahrenheit, as was measured in southeast Manitoba.
This time of year is breeding season for the beaver, and successful germination is followed by a 100-day gestation period, after which two to six kits are born. Those kits nurse from their mothers for between six and eight weeks, although they are born with teeth, fur, and open eyes. So, they are able to eat solid foods much earlier than their weaning dates, according to Seabloom’s Mammals of North Dakota.
As we hope the weather to soon turn positively springlike, a walk along a stream might be welcome- and while you’re there, maybe you’ll see a beaver dam, a tree stump topped by a comically conical point, or perhaps even a beaver itself.