Volume XVI - 1950

Beaver Dam

Wild animal life is a feature in all our national parks that every visitor enjoys observing and wants to learn more about. Whether it be a little golden-mantled ground squirrel begging for peanuts, a mama bear and her cubs parading through the campground, or a deer gracefully hurdling an obstruction by the roadside, we are tremendously absorbed and interested. Some of our most common animals are usually active at night and not ordinarily seen by man, so that their habits can only be learned through long end patient observations at unconventional hours. These animals are the more interesting once they are understood. Among these is the beaver whose life history and accomplishments present a truly amazing story. He builds dams, lodges, and canals with a skill that sometimes resembles that of man, he can fell trees three feet in diameter, and can swim a half-mile under water and his pelt is closely woven into the fabric of the early history of our country.

The beaver belongs to the same order of gnawing mammals as the ground squirrels, marmots, and mice. It is, except for the capabara of Central America, the largest rodent in the world. An individual is three to four feet long and weighs forty pounds on an average, although the exceptional individual may weigh more than seventy-five pounds.

Protruding in front of the lips are long sharp chisel-like incisors which a beaver must have to build his home and secure his food. A single beaver can rend a four-inch sapling within a few minutes using his incisors to gouge and pry out long shavings. The incisors grow throughout the life time of the animal, but the functional ends are worn by use as rapidly as they grow from the gum. If by some accident a incisor should be knocked out of place so that if failed to balance the, opposite one, the latter can become so long that the animal is unable, to open his mouth wide enough to eat, and would die of starvation.

Beaver are adapted for a life spent largely in the water. The thick muscular tail is the most conspicuous organ, and the most distinguishing part about him. It occupies about a foot of his total length, is half that wide and shaped like a paddle. Actually, the tail is used as a rudder while swimming rather than as a propelling implement. When alarmed it is used as a signal by slapping the water during the process of diving. The tail is also used for balancing, when the animal stands on its hind legs to fell trees. The hind feet are well adapted for movement in the water. They are broad and webbed like those of a duck. The reference to old timers from Oregon, the beaver state, as "web-footed" has this fact as its origin.

Beaver usually select a wide slow-moving stream or pond in which to build their homes. If such a situation is not available they create it artificially by building a dam across a stream. Alternately layers of sticks, laid parallel to the stream current, and mud are gradually made water tight as silt is added by the stream. Long dams take several seasons to build.

The most nearly typical beaver home is a house in the middle of a pond backed up by a dam. An island of mud and rock is made in the pond and a roughly circular pile of branches and mud heaped on it. The beaver then burrows up from the bottom of the island. He starts the burrow far enough below the surface of the water to be beneath the ice in the winter. The single room is then excavated and fashioned by gnawing away the interior of the stick and mud pile until the cavity is of the desired size. The interior of a house is large enough to accommodate a household of six to eight beaver. John Colter, the first white man to see the area of Yellowstone National Park, is said to have escaped from Indians by diving into a beaver house. Beaver likewise are secure from enemies in their houses isolated by water. In Crater Lake National Park beaver solve their housing problem by making burrows in stream banks.

Beaver are located on Copeland and Bybee Creeks and the lower part of Annie Creek within the park. The most immediate indication of their presence is evidence of their workings. A tree may be left standing by only the smallest splinter, completely girdled by a V-shaped cut. When the trunk is completely severed the ends of the stump and tree are cone-shaped - a sure sign that beaver are at work. Also the bases of standing trees and the whole of dead prone trees are stripped of bark. The inner layer of bark, the cambium, is the mainstay of a beaver's diet. Lodgepole pines and Douglas firs are common food in the park, although willows, alders, and aspens are taken when available.

A stand of trees close at hand and suitable for eating is as important as a pond for beaver. The supply of edible trees is the chief factor determining the length of time a home site will be occupied. Once downed, a tree is cut into lengths for transport to the pond. This may be done in canals built for the purpose, or if the distance is short the section is dragged to the water. The logs may be sunk in the mud bottom of the pond and stored for food, or used for building. Once the bark has been eaten the remainder of a log can conveniently be added to the house or dam.

The family life of beaver is a model one. They are monogamous and mate for life. A household usually consists of the two parents baby beaver born that year, and yearlings or kits. The young are born in April, and stay with the household until the second spring when they are forced by the parents to leave and start on their own. Occasionally the young will build a new house in the same pond and gradually a colony comes into being. Numbers offer protection against enemies. Thus, the river otter will attack a single beaver, but wisely refrains from molesting a whole colony. At the time the mother beaver is giving birth to her pups the father leaves the house for several weeks and leads a solitary life in a bank burrow until all the trouble is over.

The beaver has been of great value to man for his pelt and meat. Beaver pelts stimulated early exploration of North America, and were the basis for the founding of the Hudson's Bay Co. In the early days beaver pelts were a medium of exchange or barter when money was scarce or lacking. Many towns and villages in various parts of the country have the word beaver in their names, reminiscent of the part beaver played in their history. Beaver, once abounding in the streams of the north and west of North America, were trapped so extensively that many states, including Oregon, made it unlawful to trap them at any season until they once again became more abundant.

In areas in which they build numerous dams, beaver are valuable in holding the water table at a higher level, in preventing excessive erosion, and retarding runoff. After a pond has been abandoned, it fills with fine stream silt and becomes a fertile meadow excellent for farming or grazing for many years.

All of our wild animals have a fascinating life story. Many of their habits and actions seem quite logical even to our practical, opinionated minds. All our forest creatures belong to a wildlife community in which each unconsciously contributes to its stability and maintenance.