Dirk OdenDirk Oden



About SP
Science Humor





More Than Sticks and Mud

As a child I was fortunate enough to spend many of my summers at a guest ranch high in the San Juan Mountains. Near the ranch was a chain of twenty-eight beaver ponds, one of which was quite large. The pond was a major attraction for photographers looking for a beautiful reflection shot, families watching the beavers work in the evening, and of course, fishermen. From horseback on a ridge above the biggest beaver pond, riders could occasionally see a dark torpedo shape cruising near the shoreline. Rainbow trout in the five to seven pound range thrived here! While I could catch plenty of trout from the streams, small ponds, and reservoirs in the area, try as I may, I could never catch one of the lunkers in what was simply known as the Big Beaver Pond. I couldn't consider myself an accomplished angler until I caught one of its nice rainbows. The "big one" eluded me throughout my teenage years, however, and then came college and a career. A number of years had past before I found myself standing at the old shoreline of the beaver pond, fly rod in hand.

            The pond was all but gone. The beavers had long since disappeared and the dam had given in to the erosive force of the water. A stream narrow enough to straddle wound through the green grass growing in soil that had once been several feet under water. A small pool still existed near the dam and a few small brookies were rising for their evening meal. It was on the second cast to this pool that the rainbow hit. I could see right away that this was the biggest rainbow I had ever hooked. After a short fight (there was really nowhere else for him to go) I gently eased him from the water. But when I lifted up the rainbow the experience was bittersweet. A twenty-two and a half inch rainbow ought to weigh five pounds. This fish was barely two. As the beaver pond subsided over the years, the food supply had dwindled, and this once-trophy fish had been starving to death. Unable to find enough food energy to support a fish her size, she had been slowly consuming her own body to stay alive.

            In college I'm sure I studied beavers and beaver pond ecology. I probably could have recalled any number of facts about Castor canadensis and listed various ways beavers impact the environment. But it wasn't until I caught that rainbow that I really understood what I already knew. Beavers had changed a small part of the world and as a result (one of many), fish grew large. The beavers left the area and as a result (one of many), large fish began to die. There is no other animal, besides man of course, that alters the environment to the degree that beavers do and, consequently, affects so many other kinds of living things. More should come to mind when we think of beavers than sticks and mud. The beaver, then, is certainly worthy of our attention. 

Beaver Basics

            Beavers are rodents. Their closest relatives in our area are marmots and squirrels. They never stop growing during their twelve-year average life span. Although a few beavers have reached weights of over one hundred pounds, weights of forty to sixty pounds are more typical (prehistoric beavers were much larger--reaching weights of 700 pounds!). The beaver's incisors are chisel-shaped and self-sharpening, and capable of cutting through a six-inch aspen tree in about ten minutes. Beavers are strictly herbivores, eating bark, small twigs, and aquatic plants. 

Living In A Wet World

            For animals that spend most of their lives in water, beavers are able to stay remarkably dry. Their fur is coated with a waterproof oil so moisture never actually reaches the skin. The inside of their ears and nostrils can be closed to form a watertight seal when diving. Skin folds behind their incisors allowing them to cut and hold branches below the surface without taking in water. Webbed hind feet and powerful rear legs provide speed when swimming. A clear, third eyelid protects the eyes while letting the beaver see under water. Beavers are certainly well-adapted for their aquatic environment!

A Beaver's Tail

            The surest way to identify an animal as a beaver is by the tail. The wide, flat, paddle-shaped tail serves several important purposes. It is a very effective rudder, particularly when the beaver swims with a heavy log being drug on one side. As a diving plane, the tail allows the beaver to quickly change depth underwater. The tail also acts as a prop to support the beaver when feeding or cutting trees. When it perceives danger, the beaver will slap the water's surface with its tail sending a warning that can be heard half a mile away.

Why Build A Dam?

            Although beavers are well-adapted for an aquatic environment, their preferred foods are found on dry land. With the exception of river otters, which will sometimes prey on young beavers, beavers do not need to worry about predators when in the water. On dry land, though, they are easy prey for experienced predators such as mountain lions, coyotes, and bears. When a beaver builds a dam, the raised water level gives the beaver access to the newly flooded food sources and decreases the distance from trees to the safety of water. The depths of the pond provide a safe and convenient cache for storing a winter's supply of edible branches. Beavers seldom stop with just one pond, though. A chain of ponds is often created to give beavers safe access to an even larger food supply.

A Room At The Lodge

The beaver lodge, built of cut logs, branches, and mud, provides a safe year-round home for beavers. All entrances to the lodge (there are several) are under water. The living space of the lodge is above water, however, and a bedding of soft, thin wood fibers provides warmth and comfort. During the winter, the beaver can retrieve a stored branch from the bottom of the pond, return to the lodge, and feed without exposing itself to the world above the ice.

New Beginnings

In the spring, the two-year-olds will be vigorously driven from the lodge by both adults. These young beavers will usually head downstream to start their own colonies elsewhere. As the time for birth approaches, the female will temporarily chase the male (beavers usually mate for life) and last year's kits out of the lodge. She will give birth to three or four kits, which will live with the family for two years.

When Beavers Go

All beaver ponds are temporary, limited by the amount of accessible food in the area. When beavers do abandon a pond, the dam will deteriorate from lack of maintenance. Stream-born silt will fill the pond. As the water level drops new plants will begin to emerge. In time, a careful eye will be needed to find any traces of the pond in what appears to be a typical mountain meadow with a small wandering stream.

            Many living things are affected by the creation of beaver ponds. Some animals find their once-dry homes submerged and must seek shelter elsewhere. Other animals ducks for example are attracted to new beaver ponds. Deer and elk may find their game trails disrupted by beaver ponds while moose find a new place to feed on aquatic plants. Beaver ponds affect people, too. Photographers can find that perfect reflection shot. Families can walk to a pond at sundown, spread a blanket on the ground, and sit and wait for the beavers to come out of their lodge. And fishermen, if they don't wait too long, just might catch that trout of a lifetime

1997, 2006  Dirk Oden


This site was last updated 03/08/07