Beavers on creeks
Beavers on big rivers, such as those from the previous five pages, have relatively easy life
because they have readily at their disposal plenty of water of sufficient and quite stable
depth to build easily their lodge with underwater safety entrances near the river bank,
and not to have to care about anything else. They need to harvest trees for food only,
and perhaps for building the lodge, if they are not lucky enough to establish
their lodge in a suitable cavity in the river bank, for which no wood is
needed at all (as was the case of the Alberta beaver mentioned three pages back).
But most Canadian beavers do live on creeks and swamps in the middle of forests.
Quite often they will do with a creek with a small and variable flow. However, on such
a creek they have to build and constantly maintain often extensive system of dams
to create artificial lakes with sufficient and stable water depth, for which a lot
of wood is needed as building material. Also in the woods around Pinawa one can
find such dams on almost every step. (If you go there in the summer, you have to be
ready to get wet in the many swamps. Beaver structures can be recognized under the snow also
in the winter, especially if the typical cone of a beaver castle towers somewhere in the middle.)
This page contains photos from one such beaver habitat, which however has been abandoned
for at least five years, and most probably for much longer. It can be found just
east of the AECL access road, on a small creek that empties into the Winnipeg
river from the east about 3 km north of the Pinawa bridge. There are no beavers
there but, on the positive side, one can see details of beaver structures that would be
hidden under the water in a populated place.
This beaver neighbourhood consisted of a cascade of five dams with at least three wooden lodges.
The largest lodge is very well preserved, the other two were either rather small, or have been
damaged considerably since becoming abandoned. Let us walk up the stream through this place:
In the first picture is a view from the first dam. In the foreground is the pond between the first
and second dams. Behind the pond is the second dam (it is that "pile of poles" in the middle)
which, partially hidden behind the bushes that thrive on it, extends through the whole width of
the picture, and then some more on both sides. The dams have not been maintained for a long time
so that the water level behind them now fluctuates according to the water flow in the creek,
as can be seen from the broken ice cover in the foreground. (Dec. 8)
The next photo shows the same dam from above and mainly from the other, inner side facing
the accumulated water. The dam was built from branches and logs stripped of bark, which
were piled roughly parallel to the water flow. From inside (upstream) the beavers then
sealed the dam thoroughly with mud to decrease the water leakage as much as possible.
It was necessary to continually improve and repair the dams. Beavers hurried towards the
dams as soon as they registered changes in the water flow velocity or in the gurgle of the
water, caused by increased leakage of water through a portion of the dam.
See how smooth the upstream side of dam is still today in spite of not being maintained
for many years. It is of course already leaking a lot, nevertheless there still is a small
lake in front of it. (Dec. 8)
And here is the other end of the same dam which bears scars of a long-ago
catastrophe. The dam originally extended roughly along the whole length of the
diagonal of this picture - from just below its upper left corner to somewhere just a little bit
above the lower right corner. It must had been breached by a flood, after
which the beavers closed the breached section by building a brand new piece of
the dam a short distance upstream - it is that part of the dam visible in the lower
left corner of the picture. That "pile of wood" in the middle of the photo is
what remained of the original dam. One of the two small beaver castles can be
found not far from the repaired section of the dam. (Dec. 8)
Near the center of this picture is one of at least six underwater entrances
into the largest of the three castles which is built into one end of the last,
fifth dam. The castle itself occupies the right-hand side of the picture. On
the left continues the dam inside which there is another passage leading from
the castle, which comes into the open beyond the left edge of the picture. Near the right
edge of the picture one can see a third entrance. All the three entrances
led into the fourth lake created by the previous dam not far away downstream.
(Dec. 10)
A few meters to the right, there is at least one more entrance leading below
the dam, which is on the right of this picture. Above the dam there are at least two other entrances, leading
into the fifth lake. Of course, when everything was in the working
order, all these entrances were submerged under the water. Above the now dry
bottom of the fourth lake, from where the previous picture was taken, the castle
towers to the height of 2.5 m. (Jan. 26, 1999)
View of the castle from the other side, from inside the fifth lake that had
the largest area of all five beaver lakes. Its bottom is somewhat higher
(probably due to the mud accumulation behind the dam) than the bottom below the
dam. The castle is about 10 m long (I never carried with me any measure, all
lengths that I am giving here are my estimates; I only measured the width of
the river as mentioned in the introduction by driving across the bridge a few times over). (Dec. 10)
View of the same castle from farther away from the middle of now mostly dried up
bottom of the fifth lakes which the beavers created at a place where several
smaller creeds joined together. The logs near the left edge of the picture
look like a nucleus of the sixth dam which had never been finished. Not
far from there, upstream next to another creek still inside the original extent
of the fifth lake is the second small castle.
The growth of dry reddish aquatic plants waving in the wind on both sides of the
creek was originally permanently flooded by beaver lakes, and must still now
be occasionally flooded in times of high water. (Dec. 10)
All the open space around the creek and beaver-made artificial lakes was
most probably created by beaver logging. This gave rise to a new ecosystem
populated mainly by aquatic plants (see the last picture). Beavers are probably
the only living beings besides humans who are capable of making long-term and
often permanent changes to their habitat. Despite the fact that for whatever
reason did beavers leave this large a few hundred meter long clearing they
made in the forest, it will probably never return to its original
state. At the time of the maximum extent of the beaver lakes, large numbers
of aquatic plants and animals had been thriving there. As a consequence, soil
composition had changed, and a new layer of decaying organic material and
sediments had been created, which will, even after all the dams completely
disappear, support somewhat different plant system than the one that had been
there before the beavers colonized this area.
If you live in a larger Canadian city, you can view in an IMAX theatre a
beautiful movie about beavers, shot in the Kananaskis Country in Alberta
(if you live in Southern Manitoba, you can view this movie much cheaper on
request at the Oak Hammock Marsh Interpretive Centre about 30 km north of
Winnipeg). The makers of the movie must have had a lot of patience and time.
The movie starts with a journey of a young beaver couple up a mountain creek,
looking for a place to build a new dam and lodge. Then it shows them (or maybe some
other beavers) building and repairing the dam, and continually increasing the
area of their new lake. The movie makers must have gained absolute trust
of the beavers, and somehow got a camera into the beaver castle to be
able to film what was going inside the castle. The movie also shows beavers making
their winter under-the-ice trips from the castle to their stockpiles. And a
black bear's attack on a beaver who just finished cutting down a tree. The
bear had been attracted by the sound of beaver gnawing. The beaver suffered
a good bear "pat" on the back, but he managed to get into the water without
any further injuries. The angry bear then started to break through the castle
roof. It was filmed first from outside, and then a switch was made to
that camera somewhere inside the castle which showed a bear's head squeezing its way
through an ever widening hole. By that time, all the inhabitants of the castle
of course were over the hills and far away.
The large number of beaver-felled but unprocessed trees in the "beaver forest"
(two pages back) seems to indicate that also the beavers on big rivers, who
do not have to build dams, cut down more trees that what they need for food.
Maybe they have to gnaw at something all the time to keep their ever growing
teeth at an reasonable length. Most of the beavers live on small creeks, and
that may be the reason why all beavers are made by natural selection
to cut the large number of trees needed for the life on creeks and swamps in the
forests. In such places there is much less beaver-cut unused trees than
what we saw in our beaver forest near the Winnipeg River. For example, on
the abandoned beaver territory of this page I found only a few of them.
But this may not be a typical example because this place could have been abandoned
by beavers many years ago for the very reason of running out of wood. Because of the
flat surroundings, further increasing the height of dams ceased to move the shores
of their artificial lakes closer to the woods. So they used up almost to the
last chip all the wood that was available within the distance they consider
safe, and left. This is just my personal theory, that I consider the most
probable. I do not know what actually happened there.
It is also possible, that some 35 years ago the beavers had been disturbed
too much by the construction of the AECL labs a mere one kilometer from their
place. Or there was a long-term decrease in the flow of water through their creek.
If that was the case, the flow must have increased enough since then
to make possible a small beaver dam and lake only about 100 m downstream below
the first abandoned dam, just on the other side of the AECL access road.
This dam was apparently established quite recently by a young beaver couple. There
is a lot of fresh beaver stumps around. Their lodge is almost completely
underground, its position on the shore of the tiny lake is given away only
by a small mud pile sprinkled (before the snow came) all over with beaver chips.
Everything seems to be quite modest as is usually the case with young families.
Dec. 21, 2000: Unfortunately, this new beaver habitat lasted for only two years!
By the way, to let oneself being bitten by a beaver might not be very wise.
I assume that a beaver would be able to severe in one bite most of the
muscles and arteries on a person's hand, which is so much softer than a tree trunk.
