The Beaver and his Works

by Enos A. Mills, 1909

I have never been able to decide which I love best, birds or trees, but as these are really comrades it does not matter, for they can take first place together. But when it comes to second place in my affection for wild things, this, I am sure, is filled by the beaver. The beaver has so many interesting ways, and is altogether so useful, so thrifty, so busy, so skillful, and so picturesque, that I believe his life and his deeds deserve a larger place in literature and a better place in our hearts. His engineering works are of great value to man. They not only help to distribute the waters and beneficially control the flow of the streams, but they also catch and save from loss enormous quantities of the earth's best plant-food. In helping to do these two things, --governing the rivers and fixing the soil,-- he plays an important part, and if he and the forest had their way with the water-supply, floods would be prevented, streams would never run dry, and a comparatively even flow of water would be maintained in the rivers every day of the year.

A number of beaver establishing a colony made one of the most interesting exhibitions of constructive work that I have ever watched. The work went on for several weeks, and I spent hours and days in observing operations. My hiding-place on a granite crag allowed me a good view of the work, --the cutting and transportation of the little logs, the dam-building, and the house-raising. I was close to the trees that were felled. Occasionally, during the construction work of this colony, I saw several beaver at one time cutting trees near one another. Upon one occasion, one was squatted on a fallen tree, another on the limb of a live one, and a third upon a boulder, each busy cutting down his tree. In every case, the tail was used for a combination stool and brace. While cutting, the beaver sat upright and clasped the willow with fore paws or put his hands against the tree, usually tilting his head to one side. The average diameter of the trees cut was about four inches, and a tree of this size was cut down quickly and without a pause.

When the tree was almost cut off, the cutter usually thumped with his tail, at which signal all other cutters near by scampered away. But this warning signal was not always given, and in one instance an unwarned cutter had a narrow escape from a tree falling perilously close to him.

Before cutting a tree, a beaver usually paused and appeared to look at its surroundings as if choosing a place to squat or sit while cutting it down; but so far as I could tell, he gave no thought as to the direction in which the tree was going to fall. This is true of every beaver which I have seen begin cutting, and I have seen scores. But beavers have individuality, and occasionally I noticed one with marked skill or decision. It may be, therefore, that some beaver try to fell trees on a particular place. In fact, I remember having seen in two localities stumps which suggested that the beaver who cut down the trees had planned just how they were to fall. In the first locality, I could judge only from the record left by the stumps; but the quarter on which the main notch had been made, together with the fact that the notch had in two instances been made on a quarter of the tree where it was inconvenient for the cutter to work, seemed to indicate a plan to fell the tree in a particular direction. In the other locality, I knew the attitude of the trees before they were cut, and in this instance the evidence was so complete and conclusive that I must believe the beaver that cut down these trees endeavored to get them to fall in a definite direction. In each of these cases, however, judging chiefly from the teeth-marks, I think the cuttings were done by the same beaver. Many observations induce me to believe, however, that the majority of beaver do not plan how the trees are to fall.

Once a large tree is on the ground, the limbs are trimmed off and the trunk is cut into sections sufficiently small to be dragged, rolled, or pushed to the water, where transportation is easy.

The young beaver that I have seen cutting trees have worked in leisurely manner, in contrast with the work of the old ones. After giving a few bites, they usually stop to eat a piece of the bark, or to stare listlessly around for a time. As workers, young beaver appear at their best and liveliest when taking a limb from the hillside to the house in the pond. A young beaver will catch a limb by one end in his teeth, and, throwing it over his shoulder in the attitude of a puppy racing with a rope or a rag, make off to the pond. Once in the water, he throws up his head and swims to the house or the darn with the limb held trailing out over his back.

The typical beaver-house seen in the Rockies at the present time stands in the upper edge of the pond which the beaver-dam has made, near where the brook enters it. Its foundation is about eight feet across, and it stands from five to ten feet in height, a rude cone in form. Most houses are made of sticks and mud, and are apparently put up with little thought for the living-room, which is later dug or gnawed from the interior. The entrance to the house is below water-level, and commonly on the bottom of the lake. Late each autumn, the house is plastered on the outside with mud, and I am inclined to believe that this plaster is not so much to increase the warmth of the house as to give it, when the mud is frozen, a strong protective armor, an armor which will prevent the winter enemies of the beaver from breaking into the house.

Each autumn beaver pile up near by the house, a large brush-heap of green trunks and limbs, mossy of aspen, willow, cottonwood, or alder. This is their granary, and during the winter they feed upon the green bark, supplementing this with the roots of water-plants, which they drag from the bottom of the pond.

Along in May five baby beaver appear, and a little later these explore the pond and race, wrestle, and splash water in it as merrily as boys. Occasionally they sun themselves on a fallen log, or play together there, trying to push one another off into the water. Often they play in the canals that lead between ponds or from them, or on the "slides." Toward the close of summer, they have their lessons in cutting and dam-building.

A beaver appears awkward as he works on land. In use of arms and hands he reminds one of a monkey, while his clumsy and usually slow-moving body will often suggest the hippopotamus. By using head, hands, teeth, tail, and webbed feet the beaver accomplishes much. The tail of a beaver is a useful and much-used appendage; it serves as a rudder, a stool, and a ramming or signal club. The beaver may use his tail for a trowel, but I have never seen him so use it. His four front teeth are excellent edge-tools for his logging and woodwork; his webbed feet are most useful in his deep-waterway transportation, and his hands in house-building and especially in dam-building. It is in dam-building that the beaver shows his greatest skill and his best head work; for I confess to the belief that a beaver reasons. I have so often seen him change his plans so wisely and meet emergencies so promptly and well that I can think of him only as a reasoner.



Supply of winter food piled on the right


I have often wondered if beaver make a preliminary survey of a place before beginning to build a dam. I have seen them prowling suggestively along brooks just prior to beaver-dam building operations there, and circumstantial evidence would credit them with making preliminary surveys. But of this there is no proof. I have noticed a few things that seem to have been considered by beaver before beginning dam building, --the supply of food and of dam-building material, for instance, and the location of the dam so as to require the minimum amount of material and insure the creation of the largest reservoir. In making the dam, the beaver usually takes advantage of boulders, willow-clumps and surface irregularities. But he often makes errors of judgment. I have seen him abandon dams both before and after completion. The apparent reasons were that the dam either had failed or would fail to flood the area which he needed or desired flooded. His endeavors are not always successful. About twenty years ago, near Helena, Montana, a number of beaver made an audacious attempt to dam the Missouri River. After long and persistent effort, however, they gave it up. The beaver may be credited with errors, failures, and successes. He has forethought. If a colony of beaver be turned loose upon a three-mile tree-lined brook in the wilds and left undisturbed for a season, or until they have had time to select a site and locate themselves to best advantage, it is probable that the location chosen will indicate that they have examined the entire brook and then selected the best place.

As soon as the beaver's brush dam is completed, it begins to accumulate trash and mud. In a little while, usually, it is covered with a mass of soil, shrubs of willow begin to grow upon it, and after a few years it is a strong, earthy, willow-covered dam. The dams vary in length from a few feet to several hundred feet. I measured one on the South Platte River that was eleven hundred feet long. [emphasis added]

The influence of a beaver-dam is astounding. As soon as completed, it becomes a highway for the folk of the wild. It is used day and night Mice and porcupines, bears and rabbits, lions and wolves, make a bridge of it. From it, in the evening, the graceful deer cast their reflections in the quiet pond. Over it dash pursuer and pursued; and on it take place battles and courtships. It is often torn by hoof and claw of animals locked in death-struggles, and often, very often, it is stained with blood. Many a drama, picturesque, fierce, and wild, is staged upon a beaver-dam.

An interesting and valuable book could be written concerning the earth as modified and benefited by beaver action, and I have long thought that the beaver deserved at least a chapter in Marsh's masterly book, "The Earth as modified by Human Action." To "work like a beaver " is an almost universal expression for energetic persistence, but who realizes that the beaver has accomplished anything? Almost unread of and unknown are his monumental works.

The instant a beaver-dam is completed, it has a decided influence on the flow of the water and especially on the quantity of sediment which the passing water carries. The sediment, instead of going down to fill the channel below, or to clog the river's mouth, fill the harbor, and do damage a thousand miles away, is accumulated in the pond behind the dam, and a level deposit is formed over the entire area of the lake. By and by this deposit is so great that the lake is filled with sediment, but before this happens, both lake and dam check and delay so much flood-water that floods are diminished in volume, and the water thus delayed is in part added to the flow of the streams at the time of low water, the result being a more even stream-flow at all times.

The regulation of stream-flow is important. There are only a few rainy days each year, and all the water that flows down the rivers falls on these few rainy days. The instant the water reaches the earth, it is hurried away toward the sea, and unless some agency delays the run-off, the rivers would naturally contain water only on the rainy days and a little while after. The fact that some rivers contain water at all times is but evidence that something has held in check a portion of the water which fell during these rainy days.

Among the agencies which best perform the service of keeping the streams ever-flowing, are the forests and the works of the beaver. Rainfall accumulates in the brooks. The brooks conduct the water to the rivers. If across a river there be a beaver-dam, the pond formed by it will be a reservoir which will catch and retain some of the water coming into it during rainy days, and will thus delay the passage of all water which flows through it. Beaver-reservoirs are leaky ones, and if they are stored full during rainy days, the leaking helps to maintain the stream-flow in dry weather A beaver-dam thus tends to distribute to the streams below it a moderate quantity of water each day. In other words, it spreads out or distributes the water of the few rainy days through all the days of the year. A river which flows steadily throughout the year is of inestimable value to mankind. If floods sweep a river, they do damage. If low water comes, the wheels of steamers and of manufactories cease to move, and damage or death may result. In maintaining a medium between the extremes of high and low water, the beaver's work is of profound importance. In helping beneficially to control a river, the beaver would render enormous service if allowed to construct his works at its source. During times of heavy rainfall, the water-flow carries with it, especially in unforested sections, great quantities of soil and sediment Beaver-dams catch much of the material eroded from the hill-sides above, and also prevent much erosion along the streams which they govern. They thus catch and deposit in place much valuable soil, the cream of the earth, that otherwise would be washed away and lost, --washed away into the rivers and harbors, impeding navigation and increasing river and harbor bills.




There is an old Indian legend which says that after the Creator separated the land from the water he employed gigantic beavers to smooth it down and prepare it for the abode of man. This is appreciative and suggestive. Beaver-dams have had much to do with the shaping and creating of a great deal of the richest agricultural land in America. Today there are many peaceful and productive valleys the soil of which has been accumulated and fixed in place by ages of engineering activities on the part of the beaver before the white man came. On both mountain and plain you may still see much of this good work accomplished by them. In the mountains, deep and almost useless gulches have been filled by beaver-dams with sediment and in course of time changed to meadows. So far as I know, the upper course of every river in the Rockies is through a number of beaver-meadows, some of them acres in extent.

On the upper course of Grand River in Colorado, I once made an extensive examination of some old beaver-works. Series of beaver-dams had been extended along this stream for several miles, as many as twenty dams to the mile. Each succeeding dam had backed water to the one above it. These had accumulated soil and formed a series of terraces, which, with the moderate slope of the valley, had in time formed an extensive and comparatively level meadow for a great distance along the river. The beaver settlement on this river was long ago almost entirely destroyed, and the year before my arrival a cloudburst had fallen upon the mountain-slope above, and the down-rushing flood had, in places, eroded deeply into the deposits formed by the beaver-works. At one place the water had cut down twenty-two feet and had brought to light the fact that the deposit had been formed by a series of dams one above the other, a new dam having been built or the old one increased in height when the deposit of sediment had filled, or nearly filled, the pond. [emp.added] This is only one instance. There are thousands of similar places in the Rockies where beaver-dams have accumulated deposits of greater or less extent than those on the Grand River.

Only a few beaver remain, and though much of their work will endure to serve mankind, in many places their old work is gone or is going to ruin for the want of attention. We are paying dearly for the thoughtless and almost complete destruction of this animal. A live beaver is far more valuable to us than a dead one. Soil is eroding away, river-channels are filling, and most of the streams in the United States fluctuate between flood and low water. A beaver colony at the source of every stream would moderate these extremes and add to the picturesqueness and beauty of many scenes that are now growing ugly with erosion. We need to cooperate with the beaver. He would assist the work of reclamation, and be of great service in maintaining the deep-waterways. I trust he will be assisted in colonizing our National Forests, and allowed to cut timber there without a permit

The beaver is the Abou-ben-Adhem of the wild. May his tribe increase.

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