A beaver, one of a family
that lives here in this lake at the foot of the Teton Mountains
in Wyoming. While beavers can get around
perfectly well on land, they are most at home in the water, where their webbed hind feet
and large paddle-like tail make them powerful swimmers
above and below the surface. Like marmots,
beavers feed on all kinds of vegetation, and eat wood as well as leaves. And they are accomplished engineers. This great pond
is entirely their own creation. Only a few years ago, this shallow, pebbly stream
flowed straight down the valley. Then a family of beavers
moved in and built a dam. The main body of it is built of boulders. On the downstream side,
it's been lined with logs, some of them big and quite heavy, and on this side, it's been packed
with mud and vegetation. It's been built so accurately
that it is, to within a few inches, horizontal across its entire length
of about 150 yards from one side to the other.
And the lake it's created
stretches upstream for almost a mile. So important is their dam to them, that if they detect the slightest leak, usually by hearing the sound
of trickling water, they start repair work immediately. Mud is needed as well as logs. The repair team will labour away
until the leak is fully repaired. Maintaining the water at a high level
brings the beavers several advantages, one of which is that it floods
the surrounding woodlands and so enables them to swim
in safety to their main source of food.
They increase the distance
they can swim by digging channels that lead into the very heart
of the woodland. Here they can use
their sharp incisor teeth to strip off the bark
from a fallen tree trunk and nibble at it,
while still being close enough to water, to slip away
should a bear or a mountain lion turn up. Their network of channels also enables them to ferry whole branches
back to their pond. And there, where the water is deepest, they dive down and push each branch
firmly into the mud at the bottom. This is the beavers' fridge,
where the vegetation will keep fresh through the long winter
when the pond is covered with ice.
Stocking the fridge takes a lot of work and the beavers
are at their busiest in autumn. At one side of the lake,
stands their lodge, a fortress built of branches and boulders that's so strong that not even a bear
could break into it. The only entrance is through tunnels
that open underwater and the beavers take refuge here
whenever they are alarmed. That was a warning signal
to say that danger was around. That is to say me. And now I may not see the beavers
for some time. They can stay underwater
for five minutes at a time, up to 15, if they need to.
They can actually get back
to the safety of their lodge without putting their head
above the surface for a single second. Most lodges have
at least two different entrances. By October, winter is well under way, but whereas marmots
would now be hibernating, the beavers are still active and will
remain that way throughout the winter. Even when the pond ices over completely, they're still able to swim under the ice
to get back and forth to their lodge. No one knew exactly what went on
inside the lodge during winter, so when the beavers were away, we installed a couple of infrared cameras
in order to find out.
A branch from the fridge
is being brought back to the lodge for the whole family to feed on. And another. No wonder they don't need to hibernate,
with this ingenious setup. The lodge is warm and safe,
even in midwinter, and the only sign of activity
in the snug home beneath the snow is hot air rising
from the vent at the top. Inside, our cameras catch a glimpse of what, at first sight,
looks like a very small beaver. It's a muskrat. There are a pair of them in here. This is a new observation. Do the beavers actually know,
in the pitch blackness, that there are strangers among them? We noticed that the muskrats regularly
left the lodge to forage under the ice. And on several occasions, they returned a few minutes later
with a load of fresh reeds.
Perhaps the muskrats are paying rent by regularly providing
fresh bedding for the lodge. Maybe that is why the beavers accept them
and even allow them to share their food. Our infrared lights, however,
are no longer welcome, it seems..