All language subtitles for BBC.Natures.Microworlds.10of13.Yellowstone.720p.HDTV.x264.AAC.MVGroup.org Eng

Our planet is the greatest
living puzzle in the universe.

A collection of worlds
within worlds.

Each one a self-contained ecosystem
bursting with life.

But how do they work?

The intricate web of
relationships...

..and the influence
of natural forces...

..makes each microworld
complex and unique.

So, to discover their secrets, we
need to explore them one by one...

..untangle their interlocking pieces

..and ultimately reveal
the vital piece,

the key to life itself,

hidden deep within
each of Nature's Microworlds.

On a plateau high in the
Rocky Mountains of North America

sits an iconic wilderness.

Yellowstone National Park.

Cataclysmic forces
have shaped this natural wonder.

Its unique geology means that

volcanic heat from the Earth's core
comes right to the surface.

It is the most extensive
geothermal area on Earth,

with more than 10,000
thermal wonders.

Established in 1872, Yellowstone
is the world's first national park,

covering more than
8,000 square kilometres.

Aside from
its awe-inspiring landscape,

it's home to an array of North
America's most charismatic wildlife.

BEAR GROANS

WOLVES HOWL

ELK CALLS

BISON SNORTS

These dwell in vast forests
and grasslands

as well as rivers and wetlands.

Isolated by sheer mountain peaks,

this stunning microworld
is a stage upon which scientists

discovered surprising connections
between different species.

To fully understand the key
to the rich complexity of life

in Yellowstone today, we must look
at how the presence of one animal

can affect that of another.

At the very top of the food chain
in Yellowstone

is in an iconic predator.

The wolf.

The park is currently home
to 98 wolves, in ten packs.

These survive by hunting
the herds of large grazing mammals.

At the other end of the spectrum
is a humble tree-felling rodent.

The beaver.

On the face of it,

wolves and beavers
live very independent lives.

And there appears to be
no connection between them.

So it came as a surprise to find

that their fates
were somehow intertwined.

This was discovered after the
National Parks and Wildlife Service

launched a landmark project
to return wolves to Yellowstone.

Wolves were absent
from the park for 70 years.

They were eradicated as part
of a predator control campaign

aimed at protecting livestock.

But in 1995, 31 wolves were released
in a last-ditch effort

to save the species
from extinction in the wild.

The releases were surrounded
with controversy.

Some parties claimed that wolves
would unleashed devastation

upon valuable stocks
of America's rare grazing mammals.

What was to happen
was even more remarkable.

Soon after the reintroduction
of wolves,

Yellowstone's rivers
took a turn for the better.

Flows improved,
fish spawned more successfully...

..and numbers of water birds
increased.

This improvement in river habitat

was down to the tireless work
of beavers.

Beaver dams
are key to rich wetlands.

As well as providing
habitat for fish,

birds and other animals,
their precious reserves of water

improve flows through the
dry summers and remove sediments.

The timing of the beavers' return
was too closely linked

with that of the wolf
to be a coincidence.

So what is the link
between wolves and beavers?

How are their lives interconnected?

Before we answer these questions,
let's take a look

at what makes a wolf pack
a force to be reckoned with.

Winter is the wolf's time.

The relentless cold
weakens their prey.

Even so,
this elk is a formidable quarry,

standing 1.5 metres at the shoulder,
and weighing over 300 kilos.

A wolf in comparison,
only weighs about 50 kilos.

But wolves, as well as
being highly intelligent,

have the advantage of numbers
and teamwork.

The odds are stacked
in their favour.

Despite the wolves' apparent
advantage, the elk is in his prime.

And is smart.

He knows that wolves
will not risk following him

into the freezing water.

Crossing the river,
he makes good his escape...

..to the disappointment of the pack.

WOLF WHINES

A wolf pack is a close family unit.

It's led by a dominant pair
of breeding wolves,

known as the alpha pair.

As a general rule,
the other pack members

consist of their siblings
and offspring.

In a pack, only the alpha male
and female are allowed to breed.

The function of the rest of the pack
is only to help in hunting

and looking after young.

But it doesn't stop them
all playing together.

Pack hierarchy is maintained through
these ritualised play-fights.

Rank is based on attitude rather
than size or physical strength.

And there is one other way through
which they strengthen their bond.

WOLVES HOWL

Howling is used as a means
of long-distance communication.

It maintains cohesion within the
pack, even if they are separated.

And, most importantly,
it advertises their presence,

making a stamp on the territory,

and letting other wolf packs
know where their boundaries lie.

Apart from the fact that beavers
exist within wolf territory,

they have little to do with them.

Why, then,
have their numbers increased?

First, we need to look
at what Yellowstone was like

before the wolves were brought back.

Before 1995, Yellowstone's top dog
was a close cousin to the wolf.

HOWLING

The coyote.

Before wolves returned,

Yellowstone had the largest coyote
population in North America.

This had a profound
impact on the ecosystem.

Weighing in at 12 kilos,

Yellowstone's coyotes are less
than half the size of the wolves

and are not built
to tackle big prey.

They exist mainly on a diet
of small animals.

Voles and ground squirrels
are high on their menu.

They're also scavengers.

Winter casualties
are a welcome feast.

For bald eagles, winter carrion is
a welcome addition to the diet.

But, during the reign of the coyote,

they were up against
serious competition.

Thievery is another coyote trait.

These otters have hidden
their hard-earned winter catch

in a burrow under deep snow.

But it doesn't go unnoticed.

The coyote's excellent sense
of smell leads it to the prize.

They don't call coyotes
wily for nothing.

In the absence of wolves,

coyotes moved around
in the open without fear.

This fearlessness had a devastating
impact on the wider ecosystem.

And especially on one
of Yellowstone's rarest mammals...

..the pronghorn antelope.

The pronghorn is the only surviving
member of an ancient group

of animals that arose in
North America 20 million years ago.

They're quite small, standing
about one metre at the shoulder.

But what they lack in height,
they make up for in speed.

They are able to maintain speeds
of over 70 kilometres an hour

for long periods.

Coyotes are not big or fast enough
to take down an adult pronghorn,

but they do have a taste
for their calves.

Before wolves returned,

the average life expectancy of
a pronghorn fawn was just 35 days.

Coyotes swept through the herds,
taking calves,

and the pronghorn population fell
to dangerously low levels.

By the early 1990s, there was
serious concern for the pronghorn.

But all that was to change.

When the wolf returned,
coyotes were dealt a shocking blow.

Through systematic killing
and direct competition,

wolves showed the coyote
who was boss.

With coyotes firmly back
in their place,

pronghorns have been
given a respite.

Wolves pay little attention to them.

The adults are too fast

and the young are not
substantial enough to feed a pack.

So wolves set their sights
on bigger prey.

This peculiar symbiosis
has seen pronghorn numbers increase

over the wolf's range.

Coyote populations,
on the other hand,

have fallen to a fraction
of what they were before.

A more natural level.

These days,
coyotes have reverted back

to being more secretive and nervous.

They have to look
over their shoulder at every turn.

So by, policing the coyotes,

wolves have unwittingly
benefited the pronghorn,

redressing a balance.

An unforeseen consequence
of the reintroduction programme.

Were coyotes also the reason why
beavers were absent in Yellowstone?

Do beavers feature
in a coyote's diet?

Beavers don't live in the
dam itself,

but within a nearby mound built from
the same material, known as a lodge.

The lodge can only be accessed
via an underwater entrance.

Inside, safe from the attention
of predators,

they can rear their young.

With all this protection,

it's very unlikely
they'd ever encounter a coyote.

So coyotes are not
the link between wolves

and the recent success
of the beaver.

But there is one
Yellowstone predator

that is comfortable in the water and
has been known to prey upon beavers.

The bear.

There are up to 150 grizzly bears
in Yellowstone.

Big males weigh almost 300 kilos.

They are, without a doubt,
the largest predator here.

So what is the grizzly's
relationship with the wolf?

And has this had
an impact on the beaver?

Bears are omnivores,

feeding on a diet of berries,
nuts and herbs,

as well as scavenging
and hunting other animals.

They will sometimes dig open beaver
lodges and prey upon beavers.

If they really need meat,

they're more than capable
of chasing big prey like elk.

Despite their enormous bulk,
bears are surprisingly fast.

However, bears are also quite happy
to let someone else do all the work.

And, luckily for them,
wolves are a willing workforce.

Since wolves rarely eat
all of their kill in one sitting,

the carcass becomes an abandoned
picnic just waiting to be exploited.

Before wolves,

only the hardest winters would bring
a glut of carrion to the table.

With wolves,
the supply has not only increased

but is spread more evenly
throughout the year.

For bears,
this is manna from heaven.

And if they don't find
an abandoned carcass,

bears are more than capable
of stealing one.

Fear of wolves is most definitely
not on this bear's agenda.

Even a young bear
will stand up to the pack.

Despite strength in numbers,
wolves know to respect bears -

their huge jaws
and powerful claws mean business.

When the stakes are even, bears and
wolves will eat at the same table.

Wolf kills have brought
an unlikely bounty to Yellowstone.

As a result,
bear cub survival has increased.

And, despite
the obvious competition,

the bear population is on the up.

If bear predation had any impact
on beaver populations,

we'd not expect beaver numbers
to increase alongside bears'.

But they have.

So bears are not the key
to the return of the beaver.

So wolf reintroductions and the
success of beavers in Yellowstone

and not connected with either
the coyote or the bear.

With two of Yellowstone's
largest predators

removed from our list of suspects,
we must think again.

What other wolf relationships
would lead, ultimately,

to an increase in beaver numbers?

Our attention must now turn to those
animals whose lives

are far more intertwined
with those of wolves.

Their prey.

One of the animals on their menu

is Yellowstone's most iconic grazer,
the bison.

Bison are built for the freezing
Yellowstone winter.

Bulls can weigh over 1,000 kilos.
They have an attitude to match,

and will happily
stand their ground against a pack.

These giants have been roaming
the plains of North America

since the last ice age.

Their bulk allows them
to stay warm from within.

They can also slow their metabolism
right down to save energy.

Deep snow is no barrier
to these enormous beasts.

Their mighty neck muscles allow them
to bulldoze the snow away

to reach the grass beneath.

It's estimated that 50 million bison
once lived in North America...

before Europeans settled here.

Overharvesting caused total numbers
across the continent to crash

to less than 2,000 in 1900.

GUNSHOTS

Now, thanks to careful management,
their numbers across North America

have swelled again
to half a million animals.

Today, almost 4,000 live
in Yellowstone itself.

Only weak and old bison
have anything to fear from wolves.

But, during the summer months, it's
the young that are most vulnerable.

But, for wolves,
it's still a risky business.

Their strategy
is to charge the herd

and try to separate
the calves from their mothers.

But the bison are quick to react.

A large bull joins the fray.

Working together,
they form an impenetrable wall.

Any attempt at snatching a calf

could bring
fatal consequences for a wolf.

The pack realise
they've missed their chance.

The threat of serious injury
or death is always a good deterrent.

They must be successful soon,

for they themselves have young
to rear at this time of year.

It's very rare for pups
to be seen out in the open.

Spending nearly
all of their time in the den,

they only emerge when
under the protection of the pack.

A brief foray to the river
gives them a chance to play

and to view the kingdom
they'll soon rule themselves.

The alpha female
will have around six pups.

She must feed well
so that they can stay strong.

Weaned on her milk,

they're five weeks old before they
can share in the spoils of the hunt.

But for now, they must not
stay out in the open for too long.

Here, they're at risk
from bears and coyotes,

so they're soon led back to the den.

Breeding success in wolves is
strongly linked to hunting success.

If their kill rate declines, then
the wolf population soon follows.

Bison provide plenty of meat

but hunting them
pushes wolves to their limits.

Because of this, bison are not
the preferred prey of the wolf.

With bison numbers changing
little in response to wolves,

it's unlikely that they've
had a major influence

on the fortunes of beavers
and river habitat within the park.

So bison are not the link
we're looking for.

But there is one prey animal that's
inextricably linked to the wolf.

The elk.

Numbering tens of thousands,

elk are the most numerous grazer
in Yellowstone.

Late summer is the time for the rut.

The dominant male calls
to advertise his status to females

and to other males in the vicinity.

His antlers
are a sign of age and status.

ELK WAILS

Made of bone, antlers
take a lot of energy to produce -

they're shed
and regrown every year.

So they're a clear
and honest indication

of the health of an individual.

The dominant male
is clearly in his prime.

But there are challengers to the
throne and he must prove his worth.

The challenge starts
with a ritualised display

designed to size up
and intimidate an opponent.

If nobody backs down,
then contact is made.

Fights may last many minutes.
It's a dangerous time.

A well-placed antler
could mean certain death.

This time,
the competition is seen off...

..and the victor
can claim his prize.

A large male may not eat for weeks
during the rut.

All he'll do is fight.

And, if he's lucky, he'll mate with
all the females in the vicinity.

Exhausted at the end of the rut,
he has very little time to feed

and regain condition before thick
snow covers the lands once again.

And when the snows arrive,
the wolves come into their own.

Wolves hunt elk by chasing them
across open country.

This gives them time
to select their quarry.

By running the herd, the pack
can spot the weak and the slow.

Many hunts end in failure.

But, with teamwork and a bit
of luck, they can secure a meal.

With wolves,

the elk population consists
of only the healthiest animals.

In this way, wolves
and elk are interdependent.

However, before the time
of the wolf,

Yellowstone's burgeoning
elk population

grazed in open country without fear.

And here lies the key to our puzzle.

Without fear of predation by wolves,
the elk had free range

and their grazing habits
radically changed the landscape.

Especially on the river banks where
everything was grazed to the ground.

Shoots of bank-side trees
were continually pruned

and never gained a foothold.

Without trees and shrubs
strengthening the riverbanks,

erosion was rife.

This was exacerbated again
by the trampling of the herds.

Without roots,

the water-holding properties
of the soil are diminished.

And summer flows decrease.

This in turn encourages silt
to build up in fish spawning beds.

As a whole, biodiversity decreased.

Yellowstone was left with less
habitat for birds and insects,

and less fish for otters
and birds of prey.

Then along came the wolf.

The culture of fear instilled
by the wolf

returned the elk
to their naturally flighty state.

Elk no longer stay exposed
in one place for too long.

Instead, the herds stay on the move.

In their absence,
vegetation once chewed to its roots

have had a chance
to gain a foothold.

Willows, aspen and cottonwood trees
started to re-colonise river banks.

This is prime habitat
for much of Yellowstone's wildlife.

And absolutely
essential for one in particular.

The beaver.

Beaver dams encourage
the growth of aquatic plants.

These, in turn, provide food
and habitat for aquatic insects,

which themselves provide food
for birds and fish.

The enriched soil encourages
further growth of trees,

creating more nesting and feeding
sites for squirrels and birds.

The resulting ponds
act as reservoirs,

increasing water flow
during the summer months.

This provides a much better habitat
for fish to breed in.

And fish provide an important
resource for ospreys and otters.

All this is the result
of the most unlikely of connections.

That between Yellowstone's
top predator

and a shy, industrious rodent.

Yellowstone is once again
a landscape

shaped by fear of the wolf.

By saving the wolf,
human intervention has had

a far more beneficial impact
than was ever thought possible.

They control predator
and prey alike,

and have unleashed
a cascade of changes,

increasing biodiversity at
all levels of the food chain.

With wolves reinstated
as apex predator,

Yellowstone is once again
one of Earth's great microworlds.

WOLF HOWLS