Two successive dry years had greatly reduced the water-level of Lily
Lake, and the consequent shallowness of the water made a serious
situation for its beaver inhabitants. This lake covered about ten
acres, and was four feet deep in the deepest part, while over nine
tenths of the area the water was two feet or less in depth. It was
supplied by springs. Early in the autumn of 1911 the water completely
disappeared from about one half of the area, and most of the remainder
became so shallow that beaver could no longer swim beneath the
surface. This condition exposed them to the attack of enemies and made
the transportation of supplies to the house slow and difficult.
In the lake the beaver had dug an extensive system of deep
canals,--the work of years. By means of these deep canals the beaver
were able to use the place until the last, for these were full of
water even after the lake-bed was completely exposed. One day in
October while passing the lake, I noticed a coyote on the farther
shore stop suddenly, prick up his ears, and give alert attention to an
agitated forward movement in the shallow water of a canal. Then he
plunged into the water and endeavored to seize a beaver that was
struggling forward through water that was too shallow for his heavy
body. Although this beaver made his escape, other members of the
colony may not have been so fortunate.
The drouth continued and by mid-October the lake went entirely dry
except in the canals. Off in one corner stood the beaver house, a tiny
rounded and solitary hill in the miniature black plain of lake-bed.
With one exception the beaver abandoned the site and moved on to other
scenes, I know not where. One old beaver remained. Whether he did this
through the fear of not being equal to the overland journey across the
dry rocky ridge and down into Wind River, or whether from deep love of
the old home associations, no one can say. But he remained and
endeavored to make provision for the oncoming winter. Close to the
house he dug or enlarged a well that was about six feet in diameter
and four feet in depth. Seepage filled this hole, and into it he piled
a number of green aspen chunks and cuttings, a meagre food-supply for
the long, cold winter that followed. Extreme cold began in early
November, and not until April was there a thaw.
[Illustration: LAKE-BED CANALS AT LILY LAKE, OCTOBER, 1911]
[Illustration: SECTION OF A 750-FOOT CANAL AT LILY LAKE Here five feet
wide and three feet deep]
Before the lake-bed was snow-covered, all the numerous canals and
basins which the beaver had excavated could be plainly seen and
examined. The magnitude of the work which the beaver had performed in
making these is beyond comprehension. I took a series of photographs
of these excavations and made numerous measurements. To the north of
the house a pool had been dug that was three feet deep, thirty feet
long, and about twenty wide. There extended from this a canal that was
one hundred and fifty feet long. The food basin was thirty feet wide
and four feet deep. This had a canal connection with the house. In the
bottom of the basin was one of the feeble springs which supply the
lake. Another canal, which extended three hundred and fifty feet in a
northerly direction from the house, was from three to four feet wide
and three feet deep. The largest ditch or canal was seven hundred and
fifty feet long and three feet deep throughout. This extended
eastward, then northeasterly, and for one hundred feet was five feet
wide. In the remaining six hundred and fifty feet it was three to four
feet wide. There were a number of minor ditches and canals connecting
the larger ones, and altogether the extent of all made an impressive
show in the empty lake-basin.
Meantime the old beaver had a hard winter. The cold weather persisted,
and finally the well in which he had deposited winter food froze to
the bottom. Even the entrance-holes into the house were frozen shut.
This sealed him in. The old fellow, whose teeth were worn and whose
claws were bad, apparently tried in vain to break out. On returning
from three months' absence, two friends and I investigated the old
beaver's condition. We broke through the frozen walls of the house and
crawled in. The old fellow was still alive, though greatly emaciated.
For some time--I know not how long--he had subsisted on the wood and
the bark of some green sticks which had been built into an addition
of the house during the autumn. We cut several green aspens into short
lengths and threw them into the house. The broken hole was then
closed. The old fellow accepted these cheerfully. For six weeks aspens
were occasionally thrown to him, and at the end of this time the
spring warmth had melted the deep snow. The water rose and filled the
pond and unsealed the entrance to the house, and again the old fellow
emerged into the water. The following summer he was joined, or
rejoined, by a number of other beaver.
In many localities the canals or ditches dug and used by the beaver
form their most necessary and extensive works. These canals require
enormous labor and much skill. In point of interest they even excel
the house and the dam. It is remarkable that of the thousands of
stories concerning the beaver only a few have mentioned the beaver
canals. These are labor-saving improvements, and not only enable the
beaver to live easily and safely in places where he otherwise could
not live at all, but apparently they allow him to live happily. The
excavations made in taking material for house or dam commonly are
turned to useful purpose. The beaver not only builds his mound-like
house, but uses the basin thus formed in excavating earthy material
for the house for a winter food depository. Ofttimes, too, in building
the dam he does it by piling up the material dug from a ditch which
runs parallel and close to the dam, and which is useful to him as a
deep waterway after the dam is completed.
In transporting trees for food-supply, water transportation is so much
easier and safer than land, that wherever the immediate surroundings
of the pond are comparatively level the beaver endeavors to lead water
out to tree groves by digging a canal from the edge of the pond to
these groves. The felled trees are by this means easily floated into
the pond. One of the simplest forms of beaver canal is a narrow,
outward extension of the pond. This varies in length from a few yards
to one hundred feet or more.
Another and fairly common form of canal is one that is built across
low narrow necks of land which thrust out into large beaver ponds, or
on narrow stretches of land around which crooked streams wander.
The majority of beaver ponds are comparatively shallow over the
greater portion of their area. In many cases it is not easy, or even
possible, to deepen them. They may be so shallow that the pond freezes
to the bottom in winter except in its small deeper portion. The
shallow ponds are made more usable by a number of canals in the
bottom. These canals assure deep-water stretches under all conditions.
Most beaver ponds have a canal that closely parallels the dam. In some
instances this is extended around the pond a few yards inside the
shore-line. Two canals usually extend from the house. One of these
connects with the canal by the dam, the other runs to the place on the
shore (commonly at the end of a trail or slide) most visited by the
beaver.
In Jefferson Valley, Montana, not far from Three Forks, I enjoyed the
examination of numerous beaver workings, and made measurements of the
most interesting system of beaver canals that I have ever seen. The
beaver house for which these canals did service was situated on the
south bank of the river, about three feet above the summer level of
the water and about two hundred feet north of the hilly edge of the
valley. From the river a crescent-shaped canal, about thirty-five feet
in length, had been dug halfway around the base of the house.
Connected with this was a basin for winter food; this was five feet
deep and thirty-five feet in diameter. From this a canal extended
southward two hundred and seven feet. One hundred and ten feet distant
from the house was a boulder that was about ten feet in diameter. This
was imbedded in about two feet of soil. Around this boulder the canal
made a detour, and then resumed its comparatively straight line
southward.
Over the greater portion of its length this canal was four feet wide,
and at no point was it narrower than three feet. Its average depth was
twenty-eight inches. For one hundred and forty-seven feet it ran
through an approximately level stretch of the valley, and seepage
filled it with water. A low, semi-circular dam, about fifty feet in
length, crossed it at the one hundred and forty-seven-foot mark, and
served to catch and run seepage water into it, and also to act as a
wall across the canal to hold the water. The most southerly sixty feet
of this canal on the edge of the foothills ran uphill, and was about
four feet deep at the upper end, four feet higher than the end by the
house. The dam across it was supplemented by a wall forty-eight feet
further on. This wall was simply a short dam across the canal, in a
part that was inclined, and plainly for the purpose of retaining water
in the canal. The upper part of the canal was filled with water by a
streamlet from off the slope. Apparently this canal was old, for there
was growing on its banks near the house, a spruce tree, four inches in
diameter, that had grown since the canal was made.
[Illustration: Beaver Colony on Jefferson River near Three Forks,
Montana]
The wall or small dam which beaver build across canals that are
inclined represents an interesting phase of beaver development. That
these walls are built for the purpose of retaining water in the canal
appears certain. They are most numerous in canals of steepest incline,
though rarely less than twenty feet apart. I have not seen a wall in
an almost dead-level canal, except it was there for the purpose of
raising the height of the water. This wall or buttress is after all
but a dam, and like most dams it is built for the purpose of raising
and maintaining the level of water.
Extending at right angles westward from the end of the old canal was a
newer one of two hundred and twenty-one feet. A wall separated and
united the two. One hundred and sixty feet of this new canal ran along
the contour of a hill, approximately at a dead level. Then came a
wall, and from this the last sixty-one feet extended southward up a
shallow ravine. In this part there were two walls. The upper end of
the sixty-one-foot extension was nine feet higher than the house, and
four hundred and twenty-eight feet distant from it. The
two-hundred-and-twenty-one-foot extension was from twenty-six to
thirty-four inches wide, and averaged twenty-two inches deep. The
entire new part was supplied with spring water, which the beaver had
diverted from a ravine to the west and led by a seventy-foot ditch
into the upper end of their canal. Thirty feet from the end of the
canal were two burrows, evidently safe places into which the beaver
could retreat in case of sudden attack from wolves or other foe.
There were two other of these burrows, one at the outer end of the old
canal and the other alongside the boulder one hundred and ten feet
from the house.
At the time I saw these canals, the only trees near were those of an
aspen grove which surrounded the extreme end. It was autumn, and on
both tributary slopes by the end of the canal, aspens were being cut,
dragged, and rolled down these slopes into the upper end of the canal,
then floated through its waters, dragged over and across the walls,
and at last piled up for winter food in the basin by the house. In all
probability this long, large canal had been built a few yards at a
time, being extended as the trees near-by were cut down and used.
Where beaver long inhabit a locality it is not uncommon for them to
have two or three distinct and well-used trails from points on the
water's edge which lead into neighboring groves or tree-clumps. These
are the beaten tracks traveled by the beaver as they go forth from the
water for food, and over which they drag their trees and saplings
into the water. On steep slopes by the water these are called slides.
This name is also given to places in the dam over which beaver
frequently pass in their outgoings and incomings. Commonly these
trails avoid ridges and ground swells by keeping in the bottom of a
ravine; logs are cut through and rolled out of the way, or a tunnel
driven beneath; obstructions are removed, or a good way made round
them. Their log roads compare favorably with the log roads of woodsmen
who cut with steel instead of enamel.
In most old beaver colonies, where the character of the bottom of the
pond permits it, there are two or more tunnels or subways beneath the
floor of the principal pond. The main tunnel begins close to the
foundation of the house, and penetrates the earth a foot or more
beneath the water to a point on land a few feet beyond the shore-line.
If there are a number of small ponds in a colony that are separated by
fingers of land, it is not uncommon for these bits of land to be
penetrated by a thoroughfare tunnel. These tunnels through the
separating bits of land enable the beaver to go from one pond to
another without exposing themselves to dangers on land, and also
offer an easy means of intercommunication between ponds when these are
ice-covered. Pond subways also afford a place of refuge or a means of
escape in case the house is destroyed, the dam broken, or the pond
drained, or in case the pond should freeze to the bottom. Commonly
these are full of water, but some are empty. On the Missouri and other
rivers, where there are several feet of cut banks above the water,
beaver commonly dug a steeply inclined tunnel from the river's edge to
the top of a bank a few feet back.
Most of this tunnel work is hidden and remains unknown. A striking
example was in the Spruce Tree Colony, elsewhere described. These
colonists, apparently disgusted by having their ponds completely
filled with sediment which came down as the result of a cloudburst,
abandoned the old colony-site. A new site was selected on a moraine,
only a short distance from the old one. Here in the sod a basin was
scooped out, and a dam made with the excavated material. The waters
from a spring which burst forth in the moraine, about two hundred
yards up the slope and perhaps one hundred feet above, trickled down
and in due time formed a pond. The following year this pond was
enlarged, and another one built upon a terrace about one hundred feet
up the slope. From year to year there were enlargements of the old
pond and the building of new pondlets, until there were seven on the
terraces of this moraine. These, together with the connecting slides
and canals, required more water than the spring supplied, especially
in the autumn when the beaver were floating their winter supplies from
pond to pond. Within the colony area, too, were many water-filled
underground passages or subway tunnels. One of these penetrated the
turf beneath the willows for more than two hundred feet.
While watching the autumnal activities of this colony, as described in
another chapter, I broke through the surface and plunged my leg into
an underground channel or subway that was half filled with water.
Taking pains to trace this stream downward, I found that it emptied
into the uppermost of the ponds along with the waters from a small
spring. Then, tracing the channel upwards, I found that, about one
hundred and forty feet distant from the uppermost pond, it connected
with the waters of the brook on which the old colony formerly had a
place. This tunnel over most of its course was about two feet beneath
the surface, was fourteen inches in diameter, and ran beneath the
roots of spruce trees. The water which the tunnel led from the brook
plainly was being used to increase the supply needed in the canals,
ponds, and pools of the Spruce Tree Colony. The intake of this was in
a tiny pond which the beaver had formed by a damlet across the brook.
That this increased supply of water was of great advantage to the busy
and populous Spruce Tree Colony, there can be no doubt. Was this
tunnel planned and made for this especial purpose, or was the
increased water-supply of the colony the result of accident by the
brook's breaking into this subway tunnel?
The canals which beaver dig, the slides which they use, the trails
which they clear and establish, conclusively show that these animals
appreciate the importance of good waterways and good roads,--in other
words, good transportation facilities.