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Our planet is the greatest
living puzzle in the universe.
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00:00:06,000 --> 00:00:09,600
A collection of worlds
within worlds.
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Each one a self-contained ecosystem
bursting with life.
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00:00:18,000 --> 00:00:19,280
But how do they work?
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The intricate web of
relationships...
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..and the influence
of natural forces...
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..makes each microworld
complex and unique.
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So, to discover their secrets, we
need to explore them one by one...
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..untangle their interlocking pieces
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..and ultimately reveal
the vital piece,
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the key to life itself,
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00:00:50,040 --> 00:00:54,680
hidden deep within
each of Nature's Microworlds.
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On a plateau high in the
Rocky Mountains of North America
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sits an iconic wilderness.
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Yellowstone National Park.
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Cataclysmic forces
have shaped this natural wonder.
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Its unique geology means that
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volcanic heat from the Earth's core
comes right to the surface.
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It is the most extensive
geothermal area on Earth,
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with more than 10,000
thermal wonders.
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Established in 1872, Yellowstone
is the world's first national park,
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covering more than
8,000 square kilometres.
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Aside from
its awe-inspiring landscape,
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it's home to an array of North
America's most charismatic wildlife.
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BEAR GROANS
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WOLVES HOWL
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ELK CALLS
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BISON SNORTS
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These dwell in vast forests
and grasslands
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as well as rivers and wetlands.
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Isolated by sheer mountain peaks,
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this stunning microworld
is a stage upon which scientists
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discovered surprising connections
between different species.
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To fully understand the key
to the rich complexity of life
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in Yellowstone today, we must look
at how the presence of one animal
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can affect that of another.
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At the very top of the food chain
in Yellowstone
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is in an iconic predator.
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The wolf.
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The park is currently home
to 98 wolves, in ten packs.
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These survive by hunting
the herds of large grazing mammals.
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At the other end of the spectrum
is a humble tree-felling rodent.
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The beaver.
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On the face of it,
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wolves and beavers
live very independent lives.
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And there appears to be
no connection between them.
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So it came as a surprise to find
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that their fates
were somehow intertwined.
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This was discovered after the
National Parks and Wildlife Service
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launched a landmark project
to return wolves to Yellowstone.
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Wolves were absent
from the park for 70 years.
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They were eradicated as part
of a predator control campaign
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aimed at protecting livestock.
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But in 1995, 31 wolves were released
in a last-ditch effort
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to save the species
from extinction in the wild.
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The releases were surrounded
with controversy.
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Some parties claimed that wolves
would unleashed devastation
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upon valuable stocks
of America's rare grazing mammals.
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What was to happen
was even more remarkable.
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Soon after the reintroduction
of wolves,
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Yellowstone's rivers
took a turn for the better.
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Flows improved,
fish spawned more successfully...
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..and numbers of water birds
increased.
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This improvement in river habitat
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was down to the tireless work
of beavers.
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00:04:57,600 --> 00:05:00,240
Beaver dams
are key to rich wetlands.
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As well as providing
habitat for fish,
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birds and other animals,
their precious reserves of water
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00:05:06,960 --> 00:05:10,760
improve flows through the
dry summers and remove sediments.
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The timing of the beavers' return
was too closely linked
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with that of the wolf
to be a coincidence.
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So what is the link
between wolves and beavers?
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How are their lives interconnected?
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00:05:40,080 --> 00:05:43,240
Before we answer these questions,
let's take a look
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at what makes a wolf pack
a force to be reckoned with.
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Winter is the wolf's time.
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The relentless cold
weakens their prey.
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00:06:02,320 --> 00:06:05,200
Even so,
this elk is a formidable quarry,
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standing 1.5 metres at the shoulder,
and weighing over 300 kilos.
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00:06:10,120 --> 00:06:13,560
A wolf in comparison,
only weighs about 50 kilos.
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But wolves, as well as
being highly intelligent,
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have the advantage of numbers
and teamwork.
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00:06:20,680 --> 00:06:23,680
The odds are stacked
in their favour.
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00:06:29,840 --> 00:06:33,800
Despite the wolves' apparent
advantage, the elk is in his prime.
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And is smart.
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He knows that wolves
will not risk following him
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into the freezing water.
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Crossing the river,
he makes good his escape...
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..to the disappointment of the pack.
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WOLF WHINES
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A wolf pack is a close family unit.
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It's led by a dominant pair
of breeding wolves,
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known as the alpha pair.
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00:07:03,160 --> 00:07:05,440
As a general rule,
the other pack members
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consist of their siblings
and offspring.
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In a pack, only the alpha male
and female are allowed to breed.
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The function of the rest of the pack
is only to help in hunting
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and looking after young.
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00:07:21,760 --> 00:07:24,360
But it doesn't stop them
all playing together.
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Pack hierarchy is maintained through
these ritualised play-fights.
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Rank is based on attitude rather
than size or physical strength.
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And there is one other way through
which they strengthen their bond.
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WOLVES HOWL
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Howling is used as a means
of long-distance communication.
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It maintains cohesion within the
pack, even if they are separated.
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00:08:03,480 --> 00:08:07,320
And, most importantly,
it advertises their presence,
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making a stamp on the territory,
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00:08:10,160 --> 00:08:13,960
and letting other wolf packs
know where their boundaries lie.
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Apart from the fact that beavers
exist within wolf territory,
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they have little to do with them.
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Why, then,
have their numbers increased?
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00:08:28,960 --> 00:08:31,960
First, we need to look
at what Yellowstone was like
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before the wolves were brought back.
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Before 1995, Yellowstone's top dog
was a close cousin to the wolf.
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HOWLING
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The coyote.
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Before wolves returned,
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Yellowstone had the largest coyote
population in North America.
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This had a profound
impact on the ecosystem.
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Weighing in at 12 kilos,
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Yellowstone's coyotes are less
than half the size of the wolves
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and are not built
to tackle big prey.
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They exist mainly on a diet
of small animals.
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Voles and ground squirrels
are high on their menu.
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They're also scavengers.
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Winter casualties
are a welcome feast.
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For bald eagles, winter carrion is
a welcome addition to the diet.
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But, during the reign of the coyote,
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they were up against
serious competition.
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Thievery is another coyote trait.
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These otters have hidden
their hard-earned winter catch
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in a burrow under deep snow.
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But it doesn't go unnoticed.
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The coyote's excellent sense
of smell leads it to the prize.
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They don't call coyotes
wily for nothing.
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In the absence of wolves,
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coyotes moved around
in the open without fear.
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This fearlessness had a devastating
impact on the wider ecosystem.
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And especially on one
of Yellowstone's rarest mammals...
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..the pronghorn antelope.
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The pronghorn is the only surviving
member of an ancient group
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of animals that arose in
North America 20 million years ago.
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They're quite small, standing
about one metre at the shoulder.
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But what they lack in height,
they make up for in speed.
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They are able to maintain speeds
of over 70 kilometres an hour
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for long periods.
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Coyotes are not big or fast enough
to take down an adult pronghorn,
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but they do have a taste
for their calves.
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Before wolves returned,
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the average life expectancy of
a pronghorn fawn was just 35 days.
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Coyotes swept through the herds,
taking calves,
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and the pronghorn population fell
to dangerously low levels.
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By the early 1990s, there was
serious concern for the pronghorn.
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But all that was to change.
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When the wolf returned,
coyotes were dealt a shocking blow.
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Through systematic killing
and direct competition,
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wolves showed the coyote
who was boss.
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With coyotes firmly back
in their place,
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pronghorns have been
given a respite.
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Wolves pay little attention to them.
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The adults are too fast
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and the young are not
substantial enough to feed a pack.
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So wolves set their sights
on bigger prey.
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This peculiar symbiosis
has seen pronghorn numbers increase
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over the wolf's range.
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Coyote populations,
on the other hand,
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have fallen to a fraction
of what they were before.
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A more natural level.
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These days,
coyotes have reverted back
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to being more secretive and nervous.
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They have to look
over their shoulder at every turn.
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So by, policing the coyotes,
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wolves have unwittingly
benefited the pronghorn,
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redressing a balance.
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An unforeseen consequence
of the reintroduction programme.
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Were coyotes also the reason why
beavers were absent in Yellowstone?
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Do beavers feature
in a coyote's diet?
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Beavers don't live in the
dam itself,
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but within a nearby mound built from
the same material, known as a lodge.
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The lodge can only be accessed
via an underwater entrance.
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Inside, safe from the attention
of predators,
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they can rear their young.
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With all this protection,
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it's very unlikely
they'd ever encounter a coyote.
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So coyotes are not
the link between wolves
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and the recent success
of the beaver.
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But there is one
Yellowstone predator
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that is comfortable in the water and
has been known to prey upon beavers.
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The bear.
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There are up to 150 grizzly bears
in Yellowstone.
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Big males weigh almost 300 kilos.
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They are, without a doubt,
the largest predator here.
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So what is the grizzly's
relationship with the wolf?
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And has this had
an impact on the beaver?
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Bears are omnivores,
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feeding on a diet of berries,
nuts and herbs,
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as well as scavenging
and hunting other animals.
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00:14:18,520 --> 00:14:23,040
They will sometimes dig open beaver
lodges and prey upon beavers.
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00:14:24,840 --> 00:14:26,680
If they really need meat,
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00:14:26,680 --> 00:14:30,000
they're more than capable
of chasing big prey like elk.
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00:14:40,200 --> 00:14:44,080
Despite their enormous bulk,
bears are surprisingly fast.
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00:14:54,160 --> 00:14:59,160
However, bears are also quite happy
to let someone else do all the work.
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And, luckily for them,
wolves are a willing workforce.
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Since wolves rarely eat
all of their kill in one sitting,
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the carcass becomes an abandoned
picnic just waiting to be exploited.
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00:15:18,200 --> 00:15:19,640
Before wolves,
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only the hardest winters would bring
a glut of carrion to the table.
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00:15:23,880 --> 00:15:27,080
With wolves,
the supply has not only increased
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but is spread more evenly
throughout the year.
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00:15:30,360 --> 00:15:34,240
For bears,
this is manna from heaven.
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00:15:34,240 --> 00:15:36,920
And if they don't find
an abandoned carcass,
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00:15:36,920 --> 00:15:40,000
bears are more than capable
of stealing one.
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00:15:41,400 --> 00:15:45,320
Fear of wolves is most definitely
not on this bear's agenda.
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00:15:49,120 --> 00:15:52,120
Even a young bear
will stand up to the pack.
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00:15:56,160 --> 00:16:00,000
Despite strength in numbers,
wolves know to respect bears -
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00:16:00,000 --> 00:16:03,840
their huge jaws
and powerful claws mean business.
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00:16:06,280 --> 00:16:11,320
When the stakes are even, bears and
wolves will eat at the same table.
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00:16:21,560 --> 00:16:25,960
Wolf kills have brought
an unlikely bounty to Yellowstone.
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00:16:25,960 --> 00:16:29,120
As a result,
bear cub survival has increased.
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00:16:29,120 --> 00:16:31,160
And, despite
the obvious competition,
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00:16:31,160 --> 00:16:33,040
the bear population is on the up.
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00:16:35,080 --> 00:16:38,840
If bear predation had any impact
on beaver populations,
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00:16:38,840 --> 00:16:42,880
we'd not expect beaver numbers
to increase alongside bears'.
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00:16:42,880 --> 00:16:44,320
But they have.
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00:16:45,920 --> 00:16:49,520
So bears are not the key
to the return of the beaver.
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00:16:56,680 --> 00:17:01,160
So wolf reintroductions and the
success of beavers in Yellowstone
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00:17:01,160 --> 00:17:04,600
and not connected with either
the coyote or the bear.
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00:17:06,240 --> 00:17:08,360
With two of Yellowstone's
largest predators
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00:17:08,360 --> 00:17:11,880
removed from our list of suspects,
we must think again.
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00:17:11,880 --> 00:17:15,360
What other wolf relationships
would lead, ultimately,
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00:17:15,360 --> 00:17:17,440
to an increase in beaver numbers?
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00:17:20,440 --> 00:17:23,680
Our attention must now turn to those
animals whose lives
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00:17:23,680 --> 00:17:27,040
are far more intertwined
with those of wolves.
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00:17:27,040 --> 00:17:28,160
Their prey.
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00:17:32,400 --> 00:17:34,360
One of the animals on their menu
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00:17:34,360 --> 00:17:37,880
is Yellowstone's most iconic grazer,
the bison.
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00:17:40,520 --> 00:17:44,400
Bison are built for the freezing
Yellowstone winter.
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00:17:46,640 --> 00:17:51,600
Bulls can weigh over 1,000 kilos.
They have an attitude to match,
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00:17:51,600 --> 00:17:54,920
and will happily
stand their ground against a pack.
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00:17:57,320 --> 00:18:00,440
These giants have been roaming
the plains of North America
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00:18:00,440 --> 00:18:03,400
since the last ice age.
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00:18:03,400 --> 00:18:06,920
Their bulk allows them
to stay warm from within.
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00:18:08,320 --> 00:18:12,200
They can also slow their metabolism
right down to save energy.
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00:18:14,440 --> 00:18:17,840
Deep snow is no barrier
to these enormous beasts.
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00:18:20,480 --> 00:18:23,920
Their mighty neck muscles allow them
to bulldoze the snow away
246
00:18:23,920 --> 00:18:25,520
to reach the grass beneath.
247
00:18:34,200 --> 00:18:39,040
It's estimated that 50 million bison
once lived in North America...
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00:18:39,040 --> 00:18:42,200
before Europeans settled here.
249
00:18:42,200 --> 00:18:45,680
Overharvesting caused total numbers
across the continent to crash
250
00:18:45,680 --> 00:18:49,200
to less than 2,000 in 1900.
251
00:18:49,200 --> 00:18:50,680
GUNSHOTS
252
00:18:55,240 --> 00:18:59,320
Now, thanks to careful management,
their numbers across North America
253
00:18:59,320 --> 00:19:02,440
have swelled again
to half a million animals.
254
00:19:03,800 --> 00:19:07,480
Today, almost 4,000 live
in Yellowstone itself.
255
00:19:08,880 --> 00:19:13,040
Only weak and old bison
have anything to fear from wolves.
256
00:19:14,800 --> 00:19:18,920
But, during the summer months, it's
the young that are most vulnerable.
257
00:19:20,000 --> 00:19:23,240
But, for wolves,
it's still a risky business.
258
00:19:25,720 --> 00:19:28,200
Their strategy
is to charge the herd
259
00:19:28,200 --> 00:19:31,000
and try to separate
the calves from their mothers.
260
00:19:35,400 --> 00:19:38,080
But the bison are quick to react.
261
00:19:39,680 --> 00:19:41,840
A large bull joins the fray.
262
00:19:41,840 --> 00:19:45,200
Working together,
they form an impenetrable wall.
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00:19:45,200 --> 00:19:47,440
Any attempt at snatching a calf
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00:19:47,440 --> 00:19:50,160
could bring
fatal consequences for a wolf.
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00:19:53,200 --> 00:19:56,560
The pack realise
they've missed their chance.
266
00:19:58,240 --> 00:20:03,120
The threat of serious injury
or death is always a good deterrent.
267
00:20:04,520 --> 00:20:06,600
They must be successful soon,
268
00:20:06,600 --> 00:20:09,960
for they themselves have young
to rear at this time of year.
269
00:20:12,680 --> 00:20:16,640
It's very rare for pups
to be seen out in the open.
270
00:20:16,640 --> 00:20:19,320
Spending nearly
all of their time in the den,
271
00:20:19,320 --> 00:20:22,360
they only emerge when
under the protection of the pack.
272
00:20:23,800 --> 00:20:26,840
A brief foray to the river
gives them a chance to play
273
00:20:26,840 --> 00:20:29,920
and to view the kingdom
they'll soon rule themselves.
274
00:20:42,360 --> 00:20:45,080
The alpha female
will have around six pups.
275
00:20:45,080 --> 00:20:47,680
She must feed well
so that they can stay strong.
276
00:20:49,040 --> 00:20:50,280
Weaned on her milk,
277
00:20:50,280 --> 00:20:54,720
they're five weeks old before they
can share in the spoils of the hunt.
278
00:20:54,720 --> 00:20:58,200
But for now, they must not
stay out in the open for too long.
279
00:20:58,200 --> 00:21:01,000
Here, they're at risk
from bears and coyotes,
280
00:21:01,000 --> 00:21:03,640
so they're soon led back to the den.
281
00:21:05,080 --> 00:21:09,160
Breeding success in wolves is
strongly linked to hunting success.
282
00:21:13,440 --> 00:21:18,480
If their kill rate declines, then
the wolf population soon follows.
283
00:21:20,880 --> 00:21:23,200
Bison provide plenty of meat
284
00:21:23,200 --> 00:21:26,560
but hunting them
pushes wolves to their limits.
285
00:21:26,560 --> 00:21:30,760
Because of this, bison are not
the preferred prey of the wolf.
286
00:21:36,680 --> 00:21:40,160
With bison numbers changing
little in response to wolves,
287
00:21:40,160 --> 00:21:42,640
it's unlikely that they've
had a major influence
288
00:21:42,640 --> 00:21:45,880
on the fortunes of beavers
and river habitat within the park.
289
00:21:47,800 --> 00:21:50,640
So bison are not the link
we're looking for.
290
00:21:52,960 --> 00:21:57,080
But there is one prey animal that's
inextricably linked to the wolf.
291
00:21:59,440 --> 00:22:01,160
The elk.
292
00:22:07,040 --> 00:22:09,280
Numbering tens of thousands,
293
00:22:09,280 --> 00:22:12,080
elk are the most numerous grazer
in Yellowstone.
294
00:22:14,760 --> 00:22:18,160
Late summer is the time for the rut.
295
00:22:21,040 --> 00:22:24,760
The dominant male calls
to advertise his status to females
296
00:22:24,760 --> 00:22:27,160
and to other males in the vicinity.
297
00:22:28,960 --> 00:22:31,760
His antlers
are a sign of age and status.
298
00:22:32,840 --> 00:22:35,120
ELK WAILS
299
00:22:36,320 --> 00:22:40,320
Made of bone, antlers
take a lot of energy to produce -
300
00:22:40,320 --> 00:22:42,560
they're shed
and regrown every year.
301
00:22:43,600 --> 00:22:46,440
So they're a clear
and honest indication
302
00:22:46,440 --> 00:22:48,760
of the health of an individual.
303
00:22:48,760 --> 00:22:52,720
The dominant male
is clearly in his prime.
304
00:22:52,720 --> 00:22:56,680
But there are challengers to the
throne and he must prove his worth.
305
00:22:58,160 --> 00:23:00,440
The challenge starts
with a ritualised display
306
00:23:00,440 --> 00:23:04,280
designed to size up
and intimidate an opponent.
307
00:23:04,280 --> 00:23:07,960
If nobody backs down,
then contact is made.
308
00:23:15,520 --> 00:23:19,600
Fights may last many minutes.
It's a dangerous time.
309
00:23:19,600 --> 00:23:24,640
A well-placed antler
could mean certain death.
310
00:23:24,880 --> 00:23:27,640
This time,
the competition is seen off...
311
00:23:31,040 --> 00:23:33,720
..and the victor
can claim his prize.
312
00:23:38,280 --> 00:23:41,480
A large male may not eat for weeks
during the rut.
313
00:23:41,480 --> 00:23:43,840
All he'll do is fight.
314
00:23:43,840 --> 00:23:48,640
And, if he's lucky, he'll mate with
all the females in the vicinity.
315
00:23:48,640 --> 00:23:52,320
Exhausted at the end of the rut,
he has very little time to feed
316
00:23:52,320 --> 00:23:56,760
and regain condition before thick
snow covers the lands once again.
317
00:23:58,920 --> 00:24:02,840
And when the snows arrive,
the wolves come into their own.
318
00:24:07,600 --> 00:24:11,480
Wolves hunt elk by chasing them
across open country.
319
00:24:11,480 --> 00:24:14,400
This gives them time
to select their quarry.
320
00:24:17,320 --> 00:24:20,720
By running the herd, the pack
can spot the weak and the slow.
321
00:24:24,880 --> 00:24:27,840
Many hunts end in failure.
322
00:24:27,840 --> 00:24:31,200
But, with teamwork and a bit
of luck, they can secure a meal.
323
00:24:33,120 --> 00:24:34,320
With wolves,
324
00:24:34,320 --> 00:24:38,360
the elk population consists
of only the healthiest animals.
325
00:24:38,360 --> 00:24:42,160
In this way, wolves
and elk are interdependent.
326
00:24:43,720 --> 00:24:46,360
However, before the time
of the wolf,
327
00:24:46,360 --> 00:24:48,800
Yellowstone's burgeoning
elk population
328
00:24:48,800 --> 00:24:50,960
grazed in open country without fear.
329
00:24:52,280 --> 00:24:56,680
And here lies the key to our puzzle.
330
00:24:56,680 --> 00:25:01,360
Without fear of predation by wolves,
the elk had free range
331
00:25:01,360 --> 00:25:05,040
and their grazing habits
radically changed the landscape.
332
00:25:05,040 --> 00:25:09,520
Especially on the river banks where
everything was grazed to the ground.
333
00:25:09,520 --> 00:25:12,680
Shoots of bank-side trees
were continually pruned
334
00:25:12,680 --> 00:25:14,360
and never gained a foothold.
335
00:25:15,680 --> 00:25:18,160
Without trees and shrubs
strengthening the riverbanks,
336
00:25:18,160 --> 00:25:19,760
erosion was rife.
337
00:25:21,200 --> 00:25:25,160
This was exacerbated again
by the trampling of the herds.
338
00:25:26,360 --> 00:25:27,720
Without roots,
339
00:25:27,720 --> 00:25:30,200
the water-holding properties
of the soil are diminished.
340
00:25:30,200 --> 00:25:33,120
And summer flows decrease.
341
00:25:33,120 --> 00:25:38,080
This in turn encourages silt
to build up in fish spawning beds.
342
00:25:38,080 --> 00:25:41,600
As a whole, biodiversity decreased.
343
00:25:41,600 --> 00:25:45,320
Yellowstone was left with less
habitat for birds and insects,
344
00:25:45,320 --> 00:25:47,960
and less fish for otters
and birds of prey.
345
00:25:50,000 --> 00:25:52,000
Then along came the wolf.
346
00:25:53,760 --> 00:25:56,720
The culture of fear instilled
by the wolf
347
00:25:56,720 --> 00:25:59,800
returned the elk
to their naturally flighty state.
348
00:26:01,960 --> 00:26:05,680
Elk no longer stay exposed
in one place for too long.
349
00:26:05,680 --> 00:26:08,320
Instead, the herds stay on the move.
350
00:26:14,560 --> 00:26:18,000
In their absence,
vegetation once chewed to its roots
351
00:26:18,000 --> 00:26:20,360
have had a chance
to gain a foothold.
352
00:26:22,600 --> 00:26:27,400
Willows, aspen and cottonwood trees
started to re-colonise river banks.
353
00:26:31,960 --> 00:26:35,600
This is prime habitat
for much of Yellowstone's wildlife.
354
00:26:35,600 --> 00:26:38,480
And absolutely
essential for one in particular.
355
00:26:41,680 --> 00:26:43,120
The beaver.
356
00:26:44,520 --> 00:26:48,320
Beaver dams encourage
the growth of aquatic plants.
357
00:26:48,320 --> 00:26:52,400
These, in turn, provide food
and habitat for aquatic insects,
358
00:26:52,400 --> 00:26:55,880
which themselves provide food
for birds and fish.
359
00:26:58,520 --> 00:27:01,960
The enriched soil encourages
further growth of trees,
360
00:27:01,960 --> 00:27:06,080
creating more nesting and feeding
sites for squirrels and birds.
361
00:27:10,040 --> 00:27:12,760
The resulting ponds
act as reservoirs,
362
00:27:12,760 --> 00:27:15,800
increasing water flow
during the summer months.
363
00:27:17,760 --> 00:27:21,160
This provides a much better habitat
for fish to breed in.
364
00:27:21,160 --> 00:27:25,800
And fish provide an important
resource for ospreys and otters.
365
00:27:28,120 --> 00:27:32,480
All this is the result
of the most unlikely of connections.
366
00:27:32,480 --> 00:27:35,440
That between Yellowstone's
top predator
367
00:27:35,440 --> 00:27:37,880
and a shy, industrious rodent.
368
00:27:39,840 --> 00:27:43,480
Yellowstone is once again
a landscape
369
00:27:43,480 --> 00:27:45,280
shaped by fear of the wolf.
370
00:27:46,760 --> 00:27:50,000
By saving the wolf,
human intervention has had
371
00:27:50,000 --> 00:27:53,360
a far more beneficial impact
than was ever thought possible.
372
00:27:54,520 --> 00:27:58,040
They control predator
and prey alike,
373
00:27:58,040 --> 00:28:00,320
and have unleashed
a cascade of changes,
374
00:28:00,320 --> 00:28:04,320
increasing biodiversity at
all levels of the food chain.
375
00:28:07,200 --> 00:28:10,640
With wolves reinstated
as apex predator,
376
00:28:10,640 --> 00:28:15,600
Yellowstone is once again
one of Earth's great microworlds.
377
00:28:22,440 --> 00:28:25,480
WOLF HOWLS
32179
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