NOVA

Mozambique's Gorongosa National Park,

an African wilderness once ravaged by war.

In the three decades since the fighting ended,

many species' numbers have rebounded.

It's fascinating how nature works.

Now that it's coming back, to see this difference,

I have to say, it's amazing.

But things are not as idyllic as they look.

For me, as an ecologist,

things just seemed off.

Everybody's on top of everybody else.

Gorongosa is just a mess.

Why?

Scientists had a hunch that there were two vital elements

missing from the park:

large predators

and the behavior-changing fear they induce.

When you remove predators from the story,

things start to unravel.

So, in a bold plan to bring fear back to Gorongosa,

rare African wild dogsare being set free in the park.

Will they survive the relocation?

And can the science of fear help turn the tide,

transforming a damaged park intoa healthy wilderness once again?

"Nature's Fear Factor."

Right now, on "NOVA."

Beautiful.

Tranquil.

Peaceful.

Also violent.

Unforgiving.

Deadly.

A world seemingly ruled by a simple law...

Eat and be eaten.

But recently, scientists are seeing that nature's predators

add another dimension

to that picture.

Something instinctive.

Pervasive.

That something...

is fear.

New evidence about the role fear plays is changing the way

scientists look at the world.

How fear functions in nature was completely unknown,

and now we're beginning to understand

that it is actually a powerful force.

Just how powerful is being put to the test

at one national park in Mozambique,

where a bold experiment is underway:

bring back top predators to see if the fear they spread

can push the ecosystem towards a better balance

and help rescue a wilderness fighting back from the brink.

There's urgency... there's definitely urgency.

We want to really get under the hood

of the ecosystem and figure out

what's going on in a way that just wasn't possible before.

Cruising through the cloudshigh over the African continent,

a charter plane is on course with some unusual passengers.

The smell is overpowering.

And the floor is carpeted

with some of the most effective and prolific killers

in the animal world...

14 African wild dogs.

Heavily sedated, they're on a 500-mile journey

from a reserve in South Africaacross the border to Mozambique,

and their new home: Gorongosa National Park,

a protected wilderness on therebound after a tumultuous past.

Nice!

Waiting to greet them are António "Tonecas" Paulo,

the park veterinarian,

and Paola Bouley, Gorongosa's resident carnivore expert.

By this time, the wild dogs have been sedated nearly 12 hours.

They're a tough bunch,

but it's important to move quickly,

and get them safely to their prepared enclosure.

African wild dogs haven't been seen in Gorongosa

for at least 30 years.

But this park was once a familiar hunting ground.

Wild dogs, otherwise known as painted dogs, painted wolves,

have evolved on this continent

for about a million and a half years.

So they split off from dogs and wolves a long time ago.

There's nothing like them.

Okay?

There are fewer than 7,000 African wild dogs left

on the entire continent.

Tonecas, the park's top wildlife vet,

is in charge of keeping the precious animals healthy.

He's heavy.

The females and males in this group of 14

come from different packs.

When they wake up in this strange place,

there's no telling how they will react to each other.

But knowing that African wild dogs rely heavily

on their sense of smell, the team has adopted

a clever way to help defuse

potential conflict.

This is a bonding method.

By rubbing their scents on each other,

the idea is that when they wake up,

they're going to be less aggressive towards each other.

And it's been shown to really work well for wild dogs.

This is just to make this transition

a little smoother for them.

The new arrivals will be kept in this enclosure...

Called a boma... for eight weeks.

Enough time, Paola hopes, for the strangers to team up

and become Gorongosa wild dog pack number one.

Just to get these dogs here was an immense project.

We're going to be learning a lot in the next few months.

This is historic, and it could be so important

for the ecology of this park.

If all goes well, Gorongosa may provide a toehold

for this endangered species.

That, in itself, would be a victory for conservation.

How cool is that?

But these wild dogs have been hand-picked

for an even larger purpose:

to see if they can help correct

a growing imbalance in the park's ecosystem...

one caused by its tragic history.

Gorongosa is still trying to recover from a brutal war

that broke out in the 1970s.

For over 15 years, fighting between government troops

and opposition armies raged across Mozambique,

devastating the country.

The human death toll has been estimated

as high as one million.

Much of Gorongosa's 1,400- square-mile wilderness

fell under rebel control and was the scene of fierce fighting.

Once one of the most celebratedand species-rich national parks

in Africa, by the time the smoke cleared over 20 years ago,

less than ten percent of Gorongosa's large mammals

had survived the violence and poaching.

Aerial surveys returned some startling estimates:

the elephant population droppedfrom around 2,500 to about 250.

3,500 to less than 100.

200 to perhaps ten.

Other animals fared even worse:

3,500 zebra gone.

6,500 wildebeest gone.

14,000 buffalo nowhere in sight.

The devastation was so complete,

many believed Gorongosa was finished as a wilderness.

But there was one reason for hope.

The extraordinary landscape was still intact.

What makes Gorongosa really special

is the diversity of habitats.

You can go from savanna woodlands to miombo woodlands,

to open floodplain

to lake to riverine,

to gorge and mountain rainforest.

And you have that mosaic,

that complexity of habitats, that really fosters diversity.

A public-private partnership formed

the Gorongosa Restoration Project

to try and salvage the park,

recruiting an international team of scientists

to lead the effort.

When the Gorongosa Project started,

it was basically starting from scratch.

The first thing was the recovery of the species

that managed to survive, but in very low numbers.

Animals that survived the fighting

were finally free to return to their wild ways,

while some species decimated by the war,

like eland, were brought in from elsewhere.

The 14 African wild dogs

getting to know each other in the boma are the latest...

and in some ways, most challenging...

of the reintroductions.

How many collars do you have?

We have 13...

Princeton ecologist Rob Pringle is one of the scientists

working with Paola and Tonecas to make the park

a healthy wilderness once again.

Yeah.

Actually, I was saying to Tonecas,

so it would be great toget some scats

while they're stillin the boma.

Rob and other ecologists are carefully tracking

the behavior of Gorongosa's plant-eaters...

...hoping to better understand

their role in the complex web of animal interaction.

It's a living laboratory where we can bring our science

out into the field

and try to figure out the rules

that ecosystems work by.

One thing is clear about Gorongosa's herbivores:

peace is giving them a chance to recover.

In fact, their total number is approaching pre-war levels.

To the untrained eye, it looks like paradise.

But for Rob,

there have been signsthat the recovery may be veering

out of balance.

For me as an ecologist,

the first time I came to Gorongosa,

things just seemed off.

The wildlife is recovering,

but the abundance of different species is vastly different