Original subtitles

In the northern Rocky Mountains

lies Yellowstone National Park,

encompassing nearly 2.2 million acres.

Established in 1872,

it's the oldest National Park in the United States

and the first in the world.

And it is home to a unique set of fauna.

Bison were once the symbol of the vast expanses

of the Wild West.

Here, they find one of their last strongholds.

Below the surface of the ground is a gigantic magma chamber.

The park is situated atop the Yellowstone Caldera,

the largest super-volcano in North America.

It was a major habitat for wolves

until they were mercilessly exterminated 100 years ago.

Now they are back.

(wolf howls)

What has occurred since their return amounts to a unique success story.

The wolves have transformed the entire ecosystem

of Yellowstone National Park.

Yellowstone got its name

from the sulfur-rich rocks common to the area.

It remains a largely unspoiled wilderness.

But originally

Yellowstone was not set aside strictly for ecological purposes.

The park was actually created as a pleasure ground

for the enjoyment of the people.

Thus, humans created a scenic resort,

an ideal representation of wilderness.

A place where there was no room for predators like wolves.

A 100 years ago

there were such a thing as a good animal and a bad animal.

And bad animals were predators because they killed, very visibly.

Wolves, cougars, bears, coyotes, lynx, wolverine,

all those animals killed for a living.

And our mindset then was, that this is bad.

With the establishment of the National Park,

the fate of the wolves was sealed.

So they were the bad animals

and good animals were the plant eaters.

The animals that we wanted to hunt.

And so we wanted to nurture them, grow their numbers,

to expand our opportunities.

And we wanted to observe them because they were majestic

like the elk, the deer, the pronghorn and the bison.

These were beautiful animals that ate plants

and we wanted to grow them, not predators.

So wolves were eliminated from Yellowstone,

the last wolf was killed in 1926.

So we went through a 70-year period with no wolves.

From time immemorial

wolves have been considered bloodthirsty predators.

An enemy of mankind that must be exterminated.

And that's what happened, all over the world.

Yellowstone Park was no exception.

The extermination of the wolves

had catastrophic effects on the ecological equilibrium

of the park.

The elk population began to grow exponentially.

In the 1950s and 60s

the park administration tried to control the population growth

by hunting and shooting the elk.

But without success.

Without wolves, the elk had no natural enemies.

They were literally devouring Yellowstone National Park,

eating young trees before they could mature.

The northern Yellowstone elk herd,

which lives in the northern part of the park, was overpopulated.

Right after we got rid of the wolves and cougars

and bear numbers had declined,

this elk population had increased.

So the park service began controlling elk numbers themselves.

They killed thousands of elk over a 30-year period

because there were no predators.

And so that stopped in 1968

because our policy changed and public opinion changed

and so the elk population grew again.

From the late '60s to the early '90s it grew dramatically.

This one herd was over 20,000 elk.

Many people felt that was too many.

That was impacting the environment.

Something had to be done.

In the 1960s scientists fenced off this area,

to allow trees and shrubs to grow

without being eaten by elk.

The elk were a major attraction of the park

and many visitors came to see them.

But at the same time,

the growing herds were destroying the northern portion of the park.

Today, the fenced-in areas are forests,

surrounded by barren steppe.

In fact, they ate all of it down to this high.

This is what Yellowstone looked like

for the middle part of the 20th century.

The extermination of the wolves was a fatal mistake.

A bitter fight ensued.

Ultimately, the government in Washington came to a decision.

Between 1995 and 1997, wolves were captured in Canada

and reintroduced in Yellowstone National Park.

The main technique we used to keep wolves here in Yellowstone

was acclimation.

We wanted the wolves to stay in Yellowstone

and so to break that homing response

we held them in pens for 10 weeks.

And by and large it worked.

A couple of wolves took off,

but most of them stayed within Yellowstone.

So we got a total of 41 wolves from 1995 to 1997

that we let loose in this area behind me.

The wolves reclaimed Yellowstone.

And did what was expected of them:

They hunted down and preyed on the elk.

Today, the park is home to just over 100 wolves

in 11 packs.

One of them is the Wapiti Lake Pack,

which makes its home in the center of the national park.

(growls)

Led by a white alpha female, the pack sets out on the hunt.

The herd is fast.

Suddenly, one of the wolves finds itself isolated.

The hunter is now the hunted.

A fully grown, healthy elk can overpower an isolated wolf.

A kick from its hooves can be fatal.

Without the help of its pack, the wolf has no choice but to flee.

The Wapiti Lake pack retreats.

They are accustomed to hardship.

Only about one foray in five is successful.

Sometimes they have to go for weeks with nothing to eat.

It's the middle of May,

but cold weather has returned to Yellowstone.

The pack has discovered the remains of an elk carcass.

This gray wolf is Number 1091.

The white alpha wolf.

Some of these animals wear tracking collars

and are known by a number.

This helps researchers study their behavior.

There is a strict hierarchy within the pack.

There are rules about who gets to eat first.

The youngest has cut in line.

That might upset the older wolves.

The youngest wolf hesitates.

Should he relinquish the little food that is left,

and possibly go hungry?

He would rather not risk a conflict with the older wolves.

His submissive demeanor makes it clear

that he accepts the rules of the hierarchy.

And in the end, he gets his share.

For 70 years there were no wolves in the park.

So the elk had no natural enemies.

But the wolves have been back for 20 years now.

Have they succeeded where humans failed for so long?

Wolves started preying on this very large elk population right away.

And now, from 20,000 or more elk, we have in this one herd

6,000 to 7,000.

We feel that's more natural.

That's how many elk there should be.

And there's cascading effects from having fewer elk.

Those many elk really impacted the ecosystem,

and now they are more in balance with the ecosystem.

So in short, wolves and this carnivore recovery,

but wolves are the middle of it,

have in a lot of ways transformed this system.

The wolves have done their job well.

It's really an ideal success story.

But the white alpha wolf,

along with all the others wolves

roaming Yellowstone for the past 20 years,

have achieved something even more significant.

A natural balance.

Yes, they kill elk,

but they also promote life.

Coyotes play an important role here.

Without wolves, there was a huge coyote population.

They were the park's most successful predators.

And although coyotes don't kill elk,

they hunt down all the animals underneath them on the food chain.

They prey on gophers, chipmunks, squirrels, mice,

and newborn deer.

Since returning to the park, wolves have been chasing their competitors.

The number of coyotes has decreased considerably.

The beneficiaries are the North American pronghorn.

Their population has been growing since the wolves came back

and began decimating the coyotes.

Newborn pronghorn are a favorite prey of coyotes.

So fewer coyotes means more pronghorns survive.

Wolves don't bother them.

And the small mammals

gophers, chipmunks, ground squirrels can relax a bit, too.

Which is good news for foxes!

Because with fewer coyotes, there's more for them to eat.

There are more foxes in Yellowstone now too

because fewer coyotes means less competition.

And the majestic bald eagle is also seen more often.

About ten years ago their number was still decreasing.

Their primary source of nutrition, the cutthroat trout,

was in danger of dying out.

But the bald eagles found alternatives.

Now that there were fewer coyotes,

they were able to feed on squirrels, mice and weasels.

But can the wolves' reintroduction really be responsible

for the overall impact

on the entire ecosystem of the national park?

Was it a chain reaction?

From the direct prey,

the elks, to the coyotes, foxes, and even down to the mice?

Within a few years of their reintroduction,

the number of wolves had increased to 170.

For years now the number of wolves has remained steady around 100.

But are 100 wolves,

at the top of the food chain,

enough to effect such tremendous changes?

(howls)

The truth of what has happened since the wolves' return

is more complex.

They didn't just impact the fauna.

After they came back,

aspens, willows and cottonwoods began to grow again,

especially in the Northern Range of the park.

Just a few years after the wolves were reintroduced,

scientists from Oregon State University

already began noticing astounding changes in the park's flora.

Now, 20 years after the wolves returned,

these aspens reveal the true miracle

that has occurred in Yellowstone National Park.

We can see the browsing marks.

This stem has been bitten off on the top

and if we look down, we might see other evidence of this.

Here's another place it was bitten off.

This is what was suppressing the growth of young aspen

for most of the 20th century.

Amazing things have happened in the park.

For decades all that grew here were waist-high shrubs.

Now there are woods and little forests.

We can see a stand of tall, young aspen,

now growing into young trees.

These were not here 20 years ago.

If you had come to this spot in 1997,

when the wolves were being reintroduced,

there were no young aspen here taller than about waist height.

They were continually being suppressed.

And there were some aspen trees, such as this dead snag here,

but they were dying out.

Sure enough, in the northern area of the park

all that can be found growing are 100-to-150-year old as pen

or small shrubs.

The trees are never more than 5 to 6 meters tall,

and are 10 to 20 years old at the most.

There's nothing in between.

Scientists determine the exact age of the trees

to learn why these gaps exist.

Every year they record the growth of aspen

at more than 100 locations throughout the park.

With amazing results.

So it's by counting back these growth nodes,

that we were able to find out

when these tall aspen first started growing

and found that it was in the early 2000s.

Then we looked at the base and saw they used to be suppressed

but then they got released from that.

Not a complete turn off of browsing

but enough to get tall enough to continue.

This photo was taken in 2004.

Ten years later,

thick undergrowth for the first time in decades.

This photo was also taken in 2004.

Today, these willow bushes are two meters tall.

At first glance, two meters is not very impressive.

But this is the first time in a century

that aspen and willow are growing in Yellowstone at all.

The ecosystem of the national park is changing.

Is it because of the wolves?

The elk?

Can it be true that these few wolves have had such a tremendous impact?

In Lamar Valley, on the Northern Range of the park,

a wolf is preying on an elk.

The elk seems to have escaped into the middle of the river.

But wolves are patient and perseverant hunters.

They track their prey.

They know exactly when the animal is tired,

or whether it has been injured.

When a wolf preys alone,

the hunt can stretch on for hours,

sometimes even days.

The elk is injured.

But the wolf holds back.

It will probably try again within a few days.

Lamar Valley is home to the Lamar Canyon wolf pack.

The alpha female is finishing off a bison

and reacts to the howling of the rest of the pack.

(howling)

The alpha wolf wears a tracking collar identifying him as wolf 949.

His mate is pregnant.

Soon he will have to provide food for the female wolf and their young.

So the female is already teaching him

to regurgitate food he has eaten,

so he can feed her and their young later.

But there is competition with a neighboring pack.

Conflicts flare up repeatedly over the course of the winter.

These intra-species conflicts

are the most common cause of death for wolves in the national park.

The alpha female of the Lamar Canyon pack

is eyeing a young buck deer.

It is not retreating but is defending its territory.

Her son observes his mother's technique from a safe distance.

The buck doesn't seem to be intimidated.

The young wolf is still too inexperienced

to be of any help to its mother.

Finally, she decides to attack.

But the buck fights back.

No lunch today.

Even though the wolves are not always successful

the number of elk has decreased significantly.

The wolves are transforming the park.

Are they reestablishing a natural balance

that has been disturbed for an entire century?

It's summertime.

The alpha female of the Lamar Canyon pack

appears emaciated.

The young wolves she gave birth to in the spring have not survived.

They may have succumbed to illness,

or been killed by other predators.

And prey is in short supply.

The elk are still up in the high pastures,

and won't return to the valleys until late autumn.

In the first years after they were reintroduced,

the wolves found plenty of prey.

Now that the elk population has decreased so drastically,

they have to make do with less.

Wolves don't usually prey on bison.

This one probably died from an injury.

Alpha wolf 949 found it in the Lamar Valley.

But the neighboring pack

the Lamar wolves have been competing with all winter

has also picked up the scent.

A single wolf has no chance against so many opponents.

They would kill him.

The pack has discovered wolf 949.

He seems weak.

When the pack approaches, he barely manages to escape in time.

Doug Smith, the leading wolf expert at the national park,

is spending the summer with other scientists

and researchers

to determine the impact the wolves are having

on the entire ecosystem of Yellowstone,

whether the wolves are transforming not only the fauna

but also the flora of the park.

Scientists have been observing and measuring this aspen forest

since 2001.

They measure the growth from this mark each year.

There's lots of suckers. Everything was browsed.

One member of the team is Eric Larsen

from the University of Wisconsin.

Back in 1999 he was commissioned by the national park

to investigate why the aspen were disappearing.

The important thing about these aspen is,

none of these were here 20 years ago

when we reintroduced wolves.

Either these were browsed down by elk,

or they've since grown in.

So we are out here today to measure these aspen

and try and figure out what has happened.

Why has a thick forest appeared here over the past 20 years,

after decades in which nothing of the sort happened?

At first the national park researchers were puzzled.

Suddenly, aspen trees were growing

where there had been only bushes and shrubs.

From about 1700 until about 1930

there was continuous aspen regeneration on the Northern Range.

And then in 1930 something changed.

Aspen stopped reaching tree size. They were only in shrub size.

And the current on this one is 8 centimeters.

What happened back then?

To find out, they extract samples from the older trees.

The diameter gives an indication of the age of the younger trees.

The question I asked was what changed in the 1920s?

And the last recorded wolf killed in Yellowstone Park was in 1926.

So aspen stopped regenerating

at the same time the last wolf was killed in the park.

Does that mean the scientists have actually found proof

that the trees stopped growing when the last wolves were killed?

Or was something else responsible,

for example a forest fire, or climate change?

What really happened in 1926?

It's called a trophic cascade.

The reintroduction of this top predator, the wolf,

led to a reduction in the numbers and in the browsing pressure

and the behaviors of the elk population.

which, in turn, led to the aspen being able to escape browsing

and grow into tree size.

This trophic cascade

is one of the most fascinating scientific discoveries ever made.

The wolves were missing from the ecosystem.

Their reintroduction caused a chain reaction.

Well certainly wolves had a lot to do with the recovery of these aspen.

But they are not the only agent.

Cougars were gone and now they are back too.

Bears were here, but their population much reduced.

Nature is always more complex than we think.

But in this particular case a key player has been wolves.

So was the missing factor over those decades

the wolves at the top of the food chain?

Yellowstone River carries a massive amount of water.

The park is one of the most important water reservoirs

in the northwestern United States.

From raging rivers, to trickling creeks,

these waterways are the lifeline

for agriculture and livestock farming

outside the park as well.

And in Yellowstone itself

they are the basis for a highly complex ecosystem.

And within this, Mother Nature's mighty landscape architects

play a decisive role.

Beavers.

They feed primarily on willows and aspen.

They also use these trees to build their dams,

turning the smaller streams into ponds.

During the summer months, they are busy eating.

Then in the fall they repair their dams

using mud and branches,

making their lodge in the center of the dam.

And willow bushes thrive everywhere.

Since the wolf reintroduction

and the decrease in elk in this area,

and the corresponding decrease in the willows being eaten by the elk,

the willows have been able to grow tall.

Beavers have been able to use them to build these dams.

Also some of the recovering aspen.

We're starting to see a restoration of this ecological cycle

that will lead to greater expansions of these wetland complexes

and also relieve some of the restrictions of the streams.

They're narrow.

The streams will widen and connect with the banks.

All this is really good for many animal species and birds.

Ducks like to use the ponds.

Small song birds like to nest in the willow bushes.

Many animals eat the willow bushes.

Many insects thrive in this habitat.

These wetland habitats are biotopes, rich in diversity.

The primary food sources for beavers, of course,

are the thriving willow bushes.

Is that the source of the chain reaction?

Wolves decimated the elk population.

Fewer elk means fewer willow shrubs being devoured.

For centuries, beavers were rare in Yellowstone Park.

Now they are back.

And they are providing a new habitat for many other species.

Among the beneficiaries

are the great blue heron.

Others simply enjoy a chance to cool off.

Or a shortcut.

It's late August in Lamar Valley,

where Soda Butte Creek flows into the Lamar River.

Still very weak, alpha wolf 949 is crossing a meadow.

He can hardly stay on his feet,

but doesn't appear to be injured.

Twice already there have been outbreaks of a virus in the park,

and many of the wolves became ill and died.

Is he sick?

He drags himself onward until dusk falls.

Then...

he gives up.

For ten more days, wolf 949 will fight death.

When he finally shows no more signs of life,

national park rangers collect his body

before other animals and birds can get to it.

If he is carrying a disease,

any animals that eat his carcass could become infected as well.

Wolf 949 died near a road,

so it was easy to find him.

Visitors and park rangers spent the past several days here,

observing his sad life-and-death struggle.

So folks, this is 949.

He's the alpha male of the Lamar Canyon pack.

He is 6 years old.

He was born east of the park in the Beartooth pack.

H e and three other Beartooth wolves came over a year and a half ago

and joined the local pack.

And we don't know the cause of death.

He's been here for the last 13 days.

He has not been able to move or get up.

He could lift his head.

He didn't really seem to be in distress or pain.

The crew will take him to a lab in Bozeman for full analysis.

We think his younger brother will take over as the alpha male,

so it will be a pack of one adult male and two adult females.

So a small pack, but that's a functioning pack.

A few weeks later, the lab test confirmed

that wolf 949 was infected with canine distemper virus.

Autumn is descending slowly over Yellowstone National Park.

The white alpha wolf from the Wapiti Lake pack

has been spotted again in Hayden Valley,

in the heart of the park.

A few days after that the pack led by the white wolf

reveals what they have been hiding in the dense forest.

Newborn wolves, three months old,

begin tentatively exploring their surroundings.

All the baby wolves born in the Wapiti Lake pack

have survived.

Was it really the wolves that were responsible

for the trophic cascade?

Did they set the chain reaction in motion

that gave beavers more to eat,

so they created more wetlands

that in turn provided a habitat for other species?

Twenty years ago, wolves were brought in

primarily to reduce the elk population.

No one anticipated that their return would result in more forests.

No one saw this trophic cascade coming.

It really wasn't thought about a lot.

So we made predictions of what wolves were going to do,

to the elk population,

to the bison population, to the deer population,

to livestock when they left the park.

How much livestock they'd take a year.

So a lot of predictions.

There really was not any kind of prediction

on what it would do to the woody vegetation, or the grasslands.

In fact some key wolf biologists

have been critical of our research on trophic cascades.

They have said, this understanding of what wolves do to ecosystems,

is incomplete or misunderstood.

Yet this has been one of the hottest scientific topics

since wolves have been returned

and was almost not studied beforehand.

Wolves are not really very good predators.

Still, they were able to greatly reduce the elk population,

allowing the vegetation to recover in many areas of the park.

Fear might play an important role in this equation.

Even if wolves don't always kill, they still drive their prey away.

Many animals avoid areas

where they risk running into their enemies.

What the landscape of fear, that term means,

when you have an aspen forest

which is very thick, which is very hard to see into,

it changes the foraging behavior of the herbivores.

They're hesitant to enter this area

because they can be ambushed very easily by bears or by wolves.

What I have seen as I've measured aspen, is,

if you get a core of larger trees in the center

and smaller trees out on the edge,

the elk will come and they nibble on the edge

and they'll forage there

but they won't go in the center of the stand.

This helps the stand to recover.

The real rulers of Yellowstone National Park are the grizzly bears.

Apart from the wolves,

grizzlies are the most powerful predators here.

Even the wolves back down

when one of the 1500 pound giants shows up.

The only enemy the grizzlies have to fear is humans.

Two one-year-old wolves from the Wapiti Lake pack

are enjoying a meal when they are suddenly interrupted.

A grizzly appears.

The young wolves run away immediately.

One of the young wolves is a bit audacious.

But the grizzly quickly makes it clear to him

who's the boss.

It's smarter to back down

and keep a safe distance.

Meanwhile, the grizzly helps himself to the wolves' prey.

But even the grizzlies have competition.

In Hayden Valley a bear comes across a dead elk stag.

But he is not alone.

A much larger grizzly has also picked up the scent.

Knowing he is in the weaker position, the younger bear submits.

Challenging the older bear to a fight would be foolish.

A fatal faux pas.

The grizzlies enjoy an abundance of food sources here.

Until a few years ago, that included North American cutthroat trout,

before they were displaced by the non-indigenous lake trout.

In the vicinity of Yellowstone Lake,

it is becoming more and more difficult for them

to survive on the few remaining cutthroats.

Lake trout stay in the lake,

and only rarely venture upstream to spawn.

The grizzlies have often been wrongly blamed

for the decrease in the elk population.

Hunger sometimes drove the bears to kill elk calves

to replace the trout that were no longer available.

But there aren't enough bears around Yellowstone Lake to be responsible

for the long-term decrease.

Besides, they are still able to catch fish from time to time.

As the elk population decreases,

scientists hope the berry shrubs will recover.

An ideal source of nutrition for grizzlies and black bears,

who need to store a lot of fat for their winter hibernation.

But at 8,000 feet, the high altitude of the national park means

there will probably never be enough shrubs and bushes here.

Luckily there are alternative options.

In the autumn the black bears climb ever higher.

The cones of the white bark pines have a high fat content.

The bears use their climbing skills to get at them.

They let the grizzlies have the cones that fall to the ground.

The pine cones are full of calories,

so they are the best Yellowstone has to offer

to help the black bears and grizzlies store up the fat they need

to survive the long winter.

Grizzlies will eat virtually anything.

When one source of nutrition is not available

they simply turn to something else,

for example, maggots and grubs and voles and other rodents.

And baby bears know that even grass can be tasty.

So, if there are no elk around,

bears will always find something else to eat.

Occasionally the Yellowstone residents form unusual alliances.

For example, when wolves and grizzlies start the day together.

This harmonious cooperation is a partnership of convenience.

First, one of them will be the better predator,

then the other.

Still, it's always advisable to tread cautiously.

Friendship ends when they find themselves pursuing the same prey.

Now, it doesn't matter who is bigger or stronger,

but who is more stubborn.

The bison just stands by and watches them fight.

The two rivals size each other up.

The grizzly is becoming more aggressive.

But his showing off doesn't impress anyone.

(grizzly growls)

Sometimes perseverance is the best method.

Since the wolves returned to Yellowstone 20 years ago,

they have worked wonders.

They reduced the elk population from 20,000 to about 6,000.

But no one expected that their impact on the ecosystem

in the northern areas of the park

would be so far-reaching.

We're expecting that Yellowstone is never going to return

to conditions that it had in the past.

But we're actually seeing aspen stands pop up in places

with young aspen,

where they were buried in the bushes

and now they're starting to emerge.

I think we're going to see an increase

in the growth of these woody plants

as we are entering into a time of moderate browsing pressure

compared to what we used to have:

very high browsing pressure

that was suppressing them almost uniformly.

Although other factors are affecting the elk besides wolves,

this would not have happened without the wolf reintroduction.

Late September.

The young wolves of the Wapiti Lake pack

have already grown considerably.

The white alpha female

is preparing them to survive the tough winter

in Yellowstone National Park.

There are more than 20 wolves in their pack.

Whether the group stays that big

depends on whether they all find enough food,

and don't have to engage in hierarchy struggles.

Their rendezvous site is in Hayden Valley,

on the bank of the Yellowstone River.

The white wolf is the undisputed leader

and focal point of the pack.

The search for food governs their daily routine.

They hunt for prey every day,

so they can all survive the hard winter months.

Then in early October, the first snow begins to fall.

For 70 years, there were no wolves in Yellowstone.

Their extermination destroyed the entire ecosystem

of the National Park.

Now that wolves have been reintroduced,

the original natural balance is being restored.

It's truly a miracle of nature.

(howls)

Subtitles: TI:ME:CO:DE-FILMSTUDIO, Kehl