Realizing that the supply of aspens near the waters of the Moraine
Colony close to my home was almost exhausted, I wondered whether it
would be possible for the beavers to procure a sufficient supply
downstream, or whether they would deem it best to abandon this old
colony and migrate.
Out on the plains, where cottonwoods were scarce, the beavers first
cut those close to the colony, then harvested those upstream,
sometimes going a mile for them, then those downstream; but rarely
were the latter brought more than a quarter of a mile. If enemies did
not keep down the population of a colony so situated, it was only a
question of time until the scarcity of the food-supply compelled the
colonists to move either up or down stream and start anew in a place
where food trees could be obtained. But not a move until necessity
drove them!
Not far from my home in the mountains the inhabitants of two old
beaver colonies endured hardships in order to remain in the old place.
One colony, in order to reach a grove of aspens, dug a canal three
hundred and thirty-four feet long, which had an average depth of
fifteen inches and a width of twenty-six inches. It ended in a grove
of aspens, which were in due time cut down and floated through this
canal into the pond, alongside the beaver house. The other colony
endured dangers and greater hardships.
During the summer of 1900 an extensive forest fire on the northerly
slope of Long's Peak wrought great hardship among beaver colonies
along the streams in the fire district. This fire destroyed all the
aspens and some of the willows. In order to have food while a new
growth of aspens was developing, the beavers at a colony on the
Bierstadt Moraine were compelled to bring their winter supply of
aspens the distance of a quarter of a mile from an isolated grove that
had escaped the fire. This stood on a bench of the moraine at an
altitude about fifty feet greater than that of the beaver pond. Aspens
from the grove were dragged about two hundred feet, then floated
across a small water-hole, and from this taken up the steep slope of
a ridge, then down to a point about one hundred feet from the pond.
Between this place and the pond was a deep wreckage of fire-killed and
fallen spruces. To cut an avenue through these was too great a task
for the beavers; so with much labor they dug a canal beneath the wide
heap of wreckage, and through this, beneath the gigantic fallen trees,
the harvested aspens were dragged and piled in the pond for winter
food. The gathering of these harvests, even by beavers, must have been
almost a hopeless task. In going thus far from water many of the
harvesters were exposed to their enemies, and it is probable that many
beavers lost their lives.
[Illustration: THE 334-FOOT CANAL]
Beavers become strongly attached to localities and especially to their
homes. It is difficult to drive them away from these, but the
exhaustion of the food-supply sometimes compels an entire colony to
abandon the old home-site, migrate, and found a new colony. Some of
the beavers' most audacious engineering works are undertaken for the
purpose of maintaining the food-supply of the colony. It occasionally
happens that the food trees near the water by an old colony become
scarce through excessive cutting, fires, or tree diseases. In cases of
this kind the colonists must go a long distance for their supplies, or
move. They prefer to stay at the old place, and will work for weeks
and brave dangers to be able to do this. They will build a dam, dig a
new canal, clear a difficult right-of-way to a grove of food saplings,
and then drag the harvest a long distance to the water; and now and
then do all these for just one more harvest, one more year in the old
home.
The Moraine Colony had lost its former greatness. Instead of the
several ponds and the eight houses of which it had consisted twenty
years before, only one house and a single pond remained. The house was
in the deep water of the pond, about twenty feet above the dam. A
vigorous brook from Chasm Lake, three thousand feet above, ran through
the pond and poured over the dam near the house. The colony was on a
delta tongue of a moraine. Here it had been established for
generations. It was embowered in a young pine forest and had ragged
areas of willows around it. A fire and excessive cutting by beavers
had left but few aspens near the water. These could furnish food for
no more than two autumn harvests, and perhaps for only one. Other
colonies had met similar conditions. How would the Moraine Colony
handle theirs?
The Moraine colonists mastered the situation in their place with the
most audacious piece of work I have ever known beavers to plan and
accomplish. About one hundred and thirty feet south of the old pond
was a grove of aspens. Between these and the pond was a small bouldery
flat that had a scattering of dead and standing spruces and young
lodge-pole pines. A number of fallen spruces lay broken among the
partly exposed boulders of the flat. One day I was astonished to find
that a dam was being built across this flat, and still more astonished
to discover that this dam was being made of heavy sections of
fire-killed trees. Under necessity only will beavers gnaw dead wood,
and then only to a limited extent. Such had been my observations for
years; but here they were cutting dead, fire-hardened logs in a
wholesale manner. Why were they cutting this dead wood, and why a dam
across a rocky flat,--a place across which water never flowed? A dam
of dead timber across a dry flat appeared to be a marked combination
of animal stupidity,--but the beavers knew what they were doing. After
watching their activities and the progress of the dam daily for a
month, I realized that they were doing development work, with the
intention of procuring a food-supply. They completed a dam of dead
timber.
At least two accidents happened to the builders of this dead-wood dam.
One of these occurred when a tree which the beavers had gnawed off
pinned the beaver that had cut it between its end and another tree
immediately behind the animal. The other accident was caused by a tree
falling in an unexpected direction. This tree was leaning against a
fallen one that was held several feet above the earth by a boulder.
When cut off, instead of falling directly to the earth it slid
alongside the log against which it had been leaning and was shunted
off to one side, falling upon and instantly killing two of the logging
beavers.
The dam, when completed, was eighty-five feet long. It was about
fifty feet below the main pond and sixty feet distant from the south
side of it. Fifty feet of the new dam ran north and south, parallel to
the old one; then, forming a right angle, it extended thirty-five feet
toward the east. It averaged three feet in height, being made almost
entirely of large chunks, dead-tree cuttings from six to fifteen
inches in diameter and from two to twelve feet long. It appeared a
crude windrow of dead-timber wreckage.
[Illustration: Moraine Colony with Dead-Wood Dam]
The day it was completed the builders shifted the scene of activity to
the brook, a short distance below the point where it emerged from the
main pond. Here they placed a small dam across it and commenced work
on a canal, through which they endeavored to lead a part of the waters
of the brook into the reservoir which their dead-wood dam had formed.
There was a swell or slight rise in the earth of about eighteen inches
between the reservoir and the head of the canal that was to carry
water into it. The swell, I suppose, was not considered by the
beavers. At any rate, they completed about half the length of the
canal, then apparently discovered that water would not flow through
it in the direction desired. Other canal-builders have made similar
errors. The beavers were almost human. This part of the canal was
abandoned and a new start made. The beavers now apparently tried to
overcome the swell in the earth by an artificial work.
A pondlet was formed immediately below the old pond by building a
sixty-foot bow-like dam, the ends of which were attached to the old
dam. The brook pouring from the old pond quickly filled this new
narrow, sixty-foot-long reservoir. The outlet of this was made over
the bow dam at the point nearest to the waiting reservoir of the
dead-wood dam. The water, where it poured over the outlet of the bow
dam, failed to flow toward the waiting reservoir, but was shed off to
one side by the earth-swell before it. Instead of flowing southward,
it flowed eastward. The beavers remedied this and directed the flow by
building a wing dam, which extended southward from the bow dam at the
point where the water over-poured. This earthwork was about fifteen
feet long, four feet wide, and two high. Along the upper side of this
the water flowed, and from its end a canal was dug to the reservoir.
About half of the brook was diverted, and this amount of water covered
the flat and formed a pond to the height of the dead-wood dam in less
than three days. Most of the leaky openings in this dam early became
clogged with leaves, trash, and sediment that were carried in by the
water, but here and there were large openings which the beavers mudded
themselves. The new pond was a little more than one hundred feet long
and from forty to fifty feet wide. Its southerly shore flooded into
the edge of the aspen grove which the beavers were planning to
harvest.
The canal was from four to five feet wide and from eight to twenty
inches deep. The actual distance that lay between the brook and the
shore of the new pond was ninety feet. Though the diverting of the
water was a task, it required less labor than the building of the dam.
With dead timber and the canal, the beavers had labored two seasons
for the purpose of getting more supplies without abandoning the
colony. If in building the dam they had used the green, easily cut
aspens, they would have greatly reduced the available food-supply. It
would have required most of these aspens to build the dam. The only
conclusion I can reach is that the beavers not only had the
forethought to begin work to obtain a food-supply that would be needed
two years after, but also, at the expense of much labor, actually
saved the scanty near-by food-supply of aspens by making their dam
with the hard, fire-killed trees.
A large harvest of aspen and willow was gathered for winter. Daily
visits to the scene of the harvest enabled me to understand many of
the methods and much of the work that otherwise would have gone on
unknown to me. Early in the harvest an aspen cluster far downstream
was cut. Every tree in this cluster and every near-by aspen was
felled, dragged to the brook, and in this, with wrestling, pushing,
and pulling, taken upstream through shallow water,--for most mountain
streams are low during the autumn. In the midst of this work the
entrance or inlet of the canal was blocked and the bow dam was cut.
The water in the brook was almost doubled in volume by the closing
of the canal, thereby making the transportation of aspens upstream
less laborious.
[Illustration: THE DEAD-WOOD DAM, LOOKING SOUTH]
When the downstream aspens at last reposed in a pile beside the house,
harvesting was briskly begun in the aspens along the shore of the new
pond. Then came another surprise. The bow dam was repaired, and the
canal not only opened, but enlarged so that almost all the water in
the brook was diverted into the canal, through which it flowed into
the new pond.
The aspens cut on the shore of the new pond were floated across it,
then dragged up the canal into the old pond. Evidently the beavers not
only had again turned the water into the canal that they might use it
in transportation, but also had increased the original volume of water
simply to make this transportation of the aspens as easy as possible.
Their new works enabled the colonists to procure nearly five hundred
aspens for the winter. All these were taken up the new canal, dragged
over the bow and the main dams, and piled in the water by the house.
In addition to these, the aspens brought from downstream made the
total of the harvest seven hundred and thirty-two trees; and with
these went several hundred small willows. Altogether these made a
large green brush-pile that measured more than a hundred feet in
circumference, and after it settled averaged four feet in depth. This
was the food-supply for the oncoming winter. The upper surface of this
stood about one foot above the surface of the water.
Five years after the completion of this dead-wood dam it was so
overgrown with willows and grass that the original material--the dead
tree-trunks that formed the major portion of it--was completely
covered over. The new pond was used but one season. All the aspens
that were made available by the dam of the pond were cut in one
harvest. The place is now abandoned, old ponds and new.