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Beaver Lodge Construction Squad | Attenborough | BBC Earth - Video học tiếng Anh
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Beaver Lodge Construction Squad | Attenborough | BBC Earth
Beaver Lodge Construction Squad | Attenborough | BBC Earth
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0:01
A beaver, one of a family that lives here in this lake
0:05
at the foot of the Teton Mountains in Wyoming.
0:13
While beavers can get around perfectly well on land,
0:16
they are most at home in the water,
0:19
where their webbed hind feet and large paddle-like tail
0:22
make them powerful swimmers above and below the surface.
0:39
Like marmots, beavers feed on all kinds of vegetation,
0:43
and eat wood as well as leaves.
0:48
And they are accomplished engineers.
0:51
This great pond is entirely their own creation.
0:59
Only a few years ago,
1:01
this shallow, pebbly stream flowed straight down the valley.
1:05
Then a family of beavers moved in and built a dam.
1:13
The main body of it is built of boulders.
1:16
On the downstream side, it's been lined with logs,
1:20
some of them big and quite heavy,
1:22
and on this side, it's been packed with mud and vegetation.
1:27
It's been built so accurately that it is, to within a few inches,
1:31
horizontal across its entire length of about 150 yards
1:36
from one side to the other.
1:38
And the lake it's created stretches upstream for almost a mile.
1:53
So important is their dam to them,
1:55
that if they detect the slightest leak,
1:58
usually by hearing the sound of trickling water,
2:01
they start repair work immediately.
2:18
Mud is needed as well as logs.
2:35
The repair team will labour away until the leak is fully repaired.
2:44
Maintaining the water at a high level brings the beavers several advantages,
2:49
one of which is that it floods the surrounding woodlands
2:52
and so enables them to swim in safety to their main source of food.
3:03
They increase the distance they can swim by digging channels
3:08
that lead into the very heart of the woodland.
3:20
Here they can use their sharp incisor teeth
3:22
to strip off the bark from a fallen tree trunk
3:26
and nibble at it, while still being close enough to water,
3:29
to slip away should a bear or a mountain lion turn up.
4:04
Their network of channels
4:06
also enables them to ferry whole branches back to their pond.
4:28
And there, where the water is deepest,
4:30
they dive down and push each branch firmly into the mud at the bottom.
4:38
This is the beavers' fridge, where the vegetation will keep fresh
4:42
through the long winter when the pond is covered with ice.
4:54
Stocking the fridge takes a lot of work
4:57
and the beavers are at their busiest in autumn.
5:52
At one side of the lake, stands their lodge,
5:55
a fortress built of branches and boulders
5:58
that's so strong that not even a bear could break into it.
6:02
The only entrance is through tunnels that open underwater
6:05
and the beavers take refuge here whenever they are alarmed.
6:20
That was a warning signal to say that danger was around.
6:25
That is to say me.
6:27
And now I may not see the beavers for some time.
6:30
They can stay underwater for five minutes at a time,
6:33
up to 15, if they need to.
6:36
They can actually get back to the safety of their lodge
6:39
without putting their head above the surface for a single second.
6:47
Most lodges have at least two different entrances.
6:59
By October, winter is well under way,
7:02
but whereas marmots would now be hibernating,
7:05
the beavers are still active and will remain that way throughout the winter.
7:12
Even when the pond ices over completely,
7:15
they're still able to swim under the ice to get back and forth to their lodge.
7:22
No one knew exactly what went on inside the lodge during winter,
7:25
so when the beavers were away,
7:27
we installed a couple of infrared cameras in order to find out.
7:36
A branch from the fridge is being brought back to the lodge
7:40
for the whole family to feed on.
7:47
And another.
7:53
No wonder they don't need to hibernate, with this ingenious setup.
7:57
The lodge is warm and safe, even in midwinter,
8:00
and the only sign of activity in the snug home beneath the snow
8:05
is hot air rising from the vent at the top.
8:16
Inside, our cameras catch a glimpse
8:19
of what, at first sight, looks like a very small beaver.
8:25
It's a muskrat.
8:28
There are a pair of them in here.
8:30
This is a new observation.
8:34
Do the beavers actually know, in the pitch blackness,
8:37
that there are strangers among them?
8:45
We noticed that the muskrats regularly left the lodge to forage under the ice.
8:52
And on several occasions,
8:54
they returned a few minutes later with a load of fresh reeds.
9:00
Perhaps the muskrats are paying rent
9:02
by regularly providing fresh bedding for the lodge.
9:17
Maybe that is why the beavers accept them and even allow them to share their food.
9:34
Our infrared lights, however, are no longer welcome, it seems.
