Nova (1974–…): Season 47, Episode 13 - Nature's Fear Factor - full transcript

Scientists reintroduce wild dogs to Mozambique's Gorongosa National Park to see if it helps restore balance to the entire ecosystem.

Are you wondering how healthy the food you are eating is? Check it -

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.

(birds twittering)

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.

The question is: 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.

NARRATOR: 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?

(nearby snarl)
"Nature's Fear Factor."

Right now, on "NOVA."

Nature: beautiful.



(zebra yelping)

Also violent.


(deer bleating)


A world seemingly ruled
by a simple law...

(animal squeaking)

Eat and be eaten.

But recently, scientists are
seeing that nature's predators

add another dimension

to that picture.

Something instinctive.



That something...

is fear.

(bird screeching)

(speaking Portuguese):

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.

(device beeping)

NARRATOR: 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.


Waiting to greet them
are António "Tonecas" Paulo,

the park veterinarian,

and Paola Bouley, Gorongosa's
resident carnivore expert.

(indistinct chatter)

NARRATOR: 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.


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.

PAULO (speaking Portuguese):

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.

(helicopter blades whirring)

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

Aerial surveys returned
some startling estimates:

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

Hippo: 3,500 to less than 100.

Lions: 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

the Gorongosa Restoration

to try and salvage the park,

recruiting an international team
of scientists

to lead the effort.

When the Gorongosa Project

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.

(dogs chittering)

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...

NARRATOR: Princeton ecologist Rob Pringle
is one of the scientists

working with Paola and Tonecas
to make the park

a healthy wilderness once again.


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...

(shoots dart)

...hoping to better understand

their role in the complex web
of animal interaction.

(indistinct chatter)

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.

(rotor blades whirring)

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

than it was before.

Decades of research reveal
the most stable ecosystems

are those with a rich diversity
of animal life,

each species finding its place

in relative balance
with the others around it.

(warthog snorting)

But in Gorongosa,

that's not exactly
what's happening.

Some species are recovering
far more quickly than others.

The numbers of one species
in particular, waterbuck,

are absolutely exploding,

with 60,000 roaming
the floodplain and beyond...

more than ten times their number
before the war.

The ecologists are trying
to figure out

what's driving this imbalance.

Three, 20, 12.

One of the things that I'm
most interested in

is trying to understand what
we call species interaction.

This question of
how species coexist

has fascinated ecologists
for decades,

and the answers aren't easy
to figure out.

Understanding an ecosystem
this complex demands

exhaustive studies comparing
the sizes, numbers,

and behaviors of wild animals,

analyzing what they eat

and even what they leave behind.

We actually have nice,
fully formed pellets.

Each new detail
adding to the picture.

One species' strange behavior
has caught

the particular interest
of the team.

(radio static buzzing)PRINGLE: You got it?

Do you hear it?
It's very faint.

Rob and Justine Atkins
are on the hunt

for a famously skittish antelope

called a bushbuck.

Its tracking collar

emits radio signals picked up
by a hand-held antenna.


It's really strong now.

Maybe, like, 1:00.


It keeps coming in and out,

so I wonder if he's, like,
on the mound or something.

He's probably behind something.

(insects chirping)

Actually, maybe straight ahead.

They give you the slip.

They, like, sit on top
of a termite mound,

and when you approach
from one direction,

they basically slide down
off the back side.

It's super-annoying.

(insects chirping)

Sounds like he's back behind us.

Behind us again?


Okay, it's very strongright now.

Yup, there he goes,
there he goes, there he goes!

Let's see...

Oh, yeah! There he is!

And right up to a termite mound.

Onto a termite mound, oh, nice.

Oh, brilliant.

Okay, that, that's excellent.

(insects chirping)

This is more than just a game
of hide and seek.

Oh, yeah, that'll work.

NARRATOR: Rob and Justine are
rewardedwith a fresh morsel of evidence

for one of their Gorongosa

some precious bushbuck scat.

This elusive individual is
living up to its reputation...

hiding in the bush.

But the team has been surprised
to see other bushbuck

behaving much differently...

throwing caution to the wind,

venturing far
from their forest habitat

onto the open floodplain.

That struck us as very strange

to see bushbuck out in
themiddle of the wide-open plains.

We started calling them

because they were no longer
in the bush.

So when we see animals
acting differently

than we expect them to,

the first thing you have to do
is try to figure out why.

What is this telling me about
how the rules of the ecosystem

have changed,
and what does that mean

about how we manage
the ecosystem?

Rob had a hunch as to why

were leaving the forest,

and thought it might connect
with a much deeper issue

facing Gorongosa:

its relative lack
of large predators.

(snorting and growling)

In Africa, lions, hyenas,
cheetahs, leopards,

and wild dogs make up
what ecologists call

"the large predator guild."

Gorongosa once featured
nearly the full complement,

but the years of war spared
only a handful of lions.

Hyenas, wild dogs, and leopards
were either killed

or forced out by lack of prey.

Gorongosa was a wilderness
with no sharp teeth.

A bunch of things that we were
seeing in Gorongosa

seemed like signatures
of missing predators

and just animals behaving in
ways that indicated

that they had lost their fear.

The fear Rob refers to
is the fear all animals have

of becoming someone else's

perhaps the most basic instinct
in the animal world.

Until recently,
fear's role in nature

has been largely

It was thought a predator'simpact
could be easily measured:

simply count the number
of animals killed

and subtract it
from the overall population.

That's the traditional view of
how predators can affect prey.

They kill them, they eat them,
they eat their offspring.

But focusing only on killing,

as we have been doing
in the past,

we are greatly underestimatingthe
total impact that predators

might be having

out there in nature.

The successful re-introduction
of grey wolves

to Yellowstone National Park
25 years ago

led more ecologists to
attributeanother importance to predators:

the power to shape
the behavior of many

while ending the existence
of a few.

Scientists now classify
some healthy ecosystems

as "landscapes of fear"...

when the wariness predators
inspire in prey

has an impact beyond
what they kill and consume.

(wolves howling)

The landscape of fear
is a disarmingly simple idea

that seems to be applying

Oswald Schmitz
of Yale University

studies fear in
controlled settings,

using smaller and much less
exotic species than wild dogs.

His breakthrough experiments
with spiders and grasshoppers

were among the first to revealthe
surprising effects predators

can have on ecosystems.

So, there was this assumption

that the predators don't kill
enough to actually have

a huge impact on the populations
of these animals.

NARRATOR: Schmitz set up several boxes to
compare grasshopper behavior...

with spiders and without.

Those confined together
for a few weeks

seemed to prove
the old assumptions were true.

Even though the grasshoppers
were eaten by spiders,

their overall numbers
initially stayed the same

as new ones were born.

But, Schmitz found,
spiders did affect

the grasshoppers' behavior
in significant ways...

where the insects grazed
and what they ate.

And the interesting thing
that you find is that

these grasshoppers
change their diet

in the presence
of the predators.

The grasshoppers living

feasted on nutritious grass.

But when spiders
were brought in,

the hoppers moved up
into some goldenrod,

which provided them with
bettercover but less nutritious food.

Fear acted as a kind of
force field,

pushing players around the
landscape, changing the game.

SCHMITZ: When I study grasshoppers
andspiders and what they're doing,

I'm not just studying
grasshoppers and spiders.

I'm really trying to understand
the tradeoff game

that they're playing:

the tradeoff between feeding

so that you survive
and reproduce well

and avoiding predators.

That predator/prey dynamic
observed in small-scale,

tightly controlled experiments

is now being put to the test
in wild settings

with large mammals.

Some of the best studies
of the landscape of fear

are with relativelysmall
animals that you can keep

in laboratory conditions.

It's been much more
of a challenge to try to scale

that understanding up fromthe
laboratory to the real world

at the very largest scales.

And that's one of the thingswe're
trying to do in Gorongosa.

In preparation for the release
of the wild dogs,

Justine Atkins wants to know
whether the prey species'

fear responses are still active

after so many generations
with few predators around.

(insects chirping)

She sets up an experiment
using the sounds

of another top carnivore
displaced by the war: leopard.

What I'm doing right now

is going to set up a speaker
system out on the floodplain,

and what that's going to do
is play the sounds

of leopards, actually.

And what we're interested in
seeing is whether or not

the bushbuck respond,
and whether or not they change

the habitat that they're using.

Experiments with sound

are a common tool
in landscape-of-fear studies.

Scientists use them to test how
prey will react to predators

without needing the predators
to actually participate.

As a control to see whether

the antelope are simply bothered
by strange sounds,

some nights,
the speakers are programmed

to play nothing but static.

(static playing)

But on other nights,
the leopard calls sound

intermittently through
the darkness...

(leopards growling)

Using GPS signals
from collared bushbuck,

Justine is able to remotely
witness their reactions

over the course of 48 hours.

(mouse clicking)

The movements of one individual
clearly reveal

her overall findings.

When the static was broadcast,

the bushbuck seemed unfazed
by the speaker.

But when the leopard
sounds played,

it was a different story.

The speaker was in the
centerof the home range, right?

Yeah, and these blue points
are showing

where the individual was
before I deployed the speakers.

And then
what's showing in the red

are the locations where
the bushbuck was

while the sounds were playing,

while the leopard calls
were playing, at night.

Wow, that's really dramatic.

So, it's completely avoidingthis
whole area in the vicinity

of the, of the leopard noises.

Yeah, it's pretty striking,
I think.

Yeah, and this is what we saw
with all our bushbuck.

When we, when we played
the leopard calls,

they moved farther away
from where the speaker was,

and basically just avoided
using that at all.

(bird calling repeatedly
on recording)

Other ecologists studying fear
in the wild

have run similar experiments.

Liana Zanette has used
audio cues and camera traps

to test the reactions ofprey
species to predator sounds

in a South African reserve.

(bird calling continues)

While bird calls are ignored...

(lion growling on recording)

...lion growls not so much.

(growling continues)

The odd chirpings of wild dogs
set off similar alarms.

(dogs whining on recording)

If just the sounds of a predator
can change behavior,

the team is optimistic about

what the real wild dogs will do
when they are unleashed

in the park.

As the weeks pass, lead
veterinarian Tonecas Paulo

monitors the wild dogs' behavior
in the boma 'round the clock,

and treats them to regular
helpings of the local cuisine.

They don't have to hunt
for their food yet,

but carnivore director
Paola Bouley

sees clear signs
that the newcomers

are organizing themselves
into a pack.

And that an alpha male
and female are emerging

as pack leaders.

Oh, look, mating.

Or, at least, they're trying.

But you can see somethingis starting there.

PAULO: Yeah.

After seven weeks,

it becomes clear
that the alpha couple

has been doing more
than just trying.

The alpha female, named Beira,
shows signs of being pregnant.

If Beira delivers her pups
in the boma,

the pack won't leave for months.

The time has come
to set them free,

with hopes Gorongosa
will provide a good home

and the wild dogs will inject
a healthy dose of fear

back into the landscape.

Are you ready?


NARRATOR: This last free meal will be the
one to lure them out the gate.

(speaks softly)

Yeah. Let's go! Let's go!
Go! Go!

At this point we feel
a little stressed out,

but also excitement.


Oh, wait! Wait! Wait!

(speaking Portuguese):

It's all about
the perception of risk.

It's, like,
"I really want that food,

but, you know, do
I trust the situation?"

BOULEY: One's out.

Uh-huh, here we go.

Dogs don't exist solo.

They need each other,

so the pack is essential.

Once you open that gate,

can things fall apart?


You know?

Will the pack just, like,
disintegrate and disperse

and break into smaller units?

That can happen.

BOULEY: Okay...

Go, go, go, go, go!

(The Who's "I'm Free" playing)

♪ I'm free

♪ I'm free

♪ And I'm waiting for you to
follow me ♪

Beira, the pregnant
alpha female,

is the last to join the party.

She's out!

All right!

That's amazing.

♪ I'm free

♪ Oh, I'm free

♪ And I'm waiting for you

♪ To follow me

Now the experiment
truly begins.

The hunters are free to roam

in a living laboratory
as big as the great outdoors.

Several of the wild dogs
have radio collars,

but the pack is essentially
on its own.

And no one really knows
what will happen.

BOULEY: What we do know about Gorongosa
is that we have a lot of prey.

But the question is, as a pack...

'cause they hunt together...

can they successfully hunt?

Can they successfully breed,
have pups, and raise those pups,

and hunt for those pups?

Those were the milestones
that we were monitoring.

Then the other dark thought
that crosses your mind...

and this is so common
in other places...

is, dogs tend to stray
into communities,

and we are unfenced.

So, you can imagine

when wild dogs stray acrossthe
river and into communities,

what kind of chaos
that can cause, right?

It's not just a hypothetical

The rural areas
surrounding the unfenced park

are home to some 200,000 people,

many of whom depend
on farming for survival.

But their hard-earned crops
also prove irresistible

to one large and headstrong
species from the park.

(rumbling and trumpeting softly)

In the southern part of our
park, in our border,

is just a river,
which is not really

a limit or border for elephants.

Dominique Gonçalves

heads up Gorongosa's
elephant ecology program.

Oh, there he is!

She's in charge of helping

Gorongosa's elephant population
recover and thrive.

He does not have a collar.

Since the war, their numbers
have multiplied

to more than 650,
a promising rebound.

Very relaxed.

I'm not sure he's
aware of our presence.

Where is the wind going?

But keeping the elephants
within the unfenced park

is a constant battle.

This way.

Elephants have plenty to eat
in Gorongosa,

but some... especially
males looking to bulk up...

go after the tastier,
calorie-rich crops

grown around
the nearby villages.

For the farmers who depend on
their fields for survival,

elephants can be
a terrifying threat

to their lives and livelihoods.

(yelling in world language):


When the giants approach,
alarms sound.

Rapid response teams come
to defend the crops.

MAN (speaking world language):

Gorongosa ranger units
assist the locals,

supplying them with tools...
Such as fireworks...

to help frighten the elephants
out of the fields.

(fireworks popping)

(elephants trumpeting
in distance)

(fireworks boom,
elephant trumpets loudly)

But how to keep
the bulls from eating

and trampling the crops
in the first place?

With Gorongosa's help,

some farmers
began building fences

at key crossing points
along the river,

fences specially designed

to spread fear
among the giant intruders.

It's fascinating
how nature works.

As people and elephants
are afraid of each other,

also afraid of other things...

Small thing, which is bee.


To make the crops

across the river from the park

more trouble than they're worth,

the fences are booby-trapped
with beehives.

There's a wire connecting
them all,

and as the elephant
try to cross,

that shakes all the bees,
because they're all connected.

And then they come out
and attack the elephants.

African honeybees
are very aggressive.

Their sting is really painful.

The elephants also have
sensitive parts on the body;

the eyes, the trunk,
back of the ears,

so just that pain
and also the noise,

it's a natural reaction
that they have to avoid bees.

(bees buzzing)

Using camera traps,
we could see the elephants

trying to cross, shaking,
and the beehives coming,

and they're just
turning back to the park.

It's working with nature

and just understanding
the system better

to stop them,
to put more fear in elephants

so they don't go to places
where people are.

(wildlife chittering)

Back on the floodplain,
Rob thinks the brazen bushbuck

might have something in common

with the crop-raiding elephants:

that they are also leaving
their comfort zones

in pursuit of
more nourishing food.

But to test the idea,

Rob needs to know what
these "plainsbuck" are eating.

Some impala pellets here.

we don't know a lot

about what these animals
actually eat in the wild.

How do you figure it out?

You can try to do it by
just watching the animals.

That's more problematic
than it might sound,

because identifying plants
is really tricky.

Just in the floodplain
behind me, you know,

there are
hundreds of plant species,

and some of them are
coexisting side by side.

Even for somebody
with a PhD in botany,

it can be very difficult
to figure out

what is this
plant species' name,

much less for, you know,

an ecologist who
mainly studies antelope.

NARRATOR: It turns out the surest
wayto know what goes into an animal

is to sort
through what comes out.

Okay, Gorongosa...

Over the years, more than
3,000 fecal samples

have been collected in the park.

The droppings
produced in Gorongosa

end up 8,000 miles away,
in Princeton, New Jersey.

Here, they are put
through a process called

DNA meta-barcoding.

When the herbivore eats food,

digests it,
it doesn't digest everything.

It leaves behind quite a lot of

DNA of the food that it ate.

This deep dive

into Gorongosa dung
is a key step

in understanding
the eating habits

of the park's herbivores.

So right there

in this little drop of liquid

is all of the DNA that
we'veextracted from our fecal sample.

In that DNA is encompassed

everything that the bushbuck
had been eating

for the last couple of days.

Once the DNA molecules are

they're sequenced
and compared with a database

to decipher exactly which plants

the animal has ingested.

And so, we're able
to sequence that DNA

and identify the plant species

so that we have an idea of
how much of a given food

that animal had been eating.

NARRATOR: The Pringle lab data reveal that

the bushbuck on the floodplain
are eating better than

their counterparts
in the forest.

PRINGLE: The bolder individuals who were
more willing to take risks

were reaping this huge reward

of being out in the floodplain,
growing large,

and presumably
having lots of babies.

With few predators around,
what's to stop them?

The more Matt Hutchinson
studies the data,

the more he sees that bushbuck
aren't the only ones

in Gorongosa behaving strangely.

Matt isolates the eating habits

of the park's
main herbivore species.

Then he compares them with data

from a similar but more stable
ecosystem in Kenya.

The Kenyan herbivores have

distinct and separate
eating habits.

Each species has established
a specialized diet

and is sticking to it.

In Kenya, there's a very clear

between who eats grass
and who eats trees and shrubs,

which is more or less
what we would expect

in a mature ecosystemwith
separation of diet.

Each species gota very characteristic diet

that doesn't really overlap

that much with the other ones.

But Matt's data from Gorongosa

reveal a different story.

This Gorongosa pattern
is really exceptional,

because their diets
are running together,

they're overlapping,

and everybody's
out of their lane

and colliding with each other.

Gorongosa is just a mess.

Everybody's on top ofeverybody else.

Gorongosa's overlapping
eating patterns

are more than just a curiosity.

Several herbivore species
pursuing the same plants

sets up a situation of
all competing against all:

an ecosystem out of balance.

The big glaring difference

between Gorongosa
and all these other places

is that Gorongosa
hasn't had big carnivores

until just recently.

When there's
no landscape of fear,

that is enabling the prey
to basically

go everywhere in the landscape
and eat everything,

and the conventional lanes
and boundaries that we see

between species
in other ecosystems

have broken down.

(animal shrieking)

And that's where

the African wild dogs come in,

to help re-establish order

among species that have been

feeding and breeding
without restraint.

But for that, they're
going to need reinforcements.

Paola and Tonecas
keep daily tabs

on Beira's GPS collar data

as she travels through the park.

They know she's searchingfor
a place to establish a den,

where she can give birth to
her litter of pups.

It isn't long
before they get a clue.

Beira's GPS collar stops
transmitting for a few days,

then several data points pop
upall at once and close together.

The collar disappears,

so it stops pinging, because

underground, it just can't
connect with the satellite.

But as soon as she emerges,

the data downloads,
and we see a cluster.

So, you see thatshe's
concentrating in one area,

and that's
a strong sign of a den.

But within days,
Beira's GPS signal

indicates trouble.

She seems to
have abandoned the den.

At some point,
she left and never went back,

and it's, like, okay,
what happened here?

'Cause it's too soon, you know?

They spend months on a den.

And we began searching for
evidence as to why.

A camera trap placed near
the den entrance

captures Paola as she discovers
the cause of the problem.

I wanted to go check out
what was going on.

But I was thinking,
maybe we could fish out

a little bit more evidence

to suggest that the pups
were in fact in that den.

And when I stick my head
in there,

I kind of hear something

drop out of the trees
on top of me.


And boom,

I'm face to face with
this big snake

that just goes
straight into the den.

What had briefly been
the wild dogs' den

was now home to
an African rock python.

And unfortunately,

all evidence suggests
the python took the pups.


Dogs have no defense
against a snake like that.

Fortunately, Beira, the alpha
female, survived.

It's a disappointing setback

in the effort
to re-establish wild dogs

in Gorongosa.

But out here,

death comes with the territory.

That's natural.

In nature, lions, snake,

fire gonna impact
reproduction for dogs.

As long as it's natural,
we let things run its course.

It's the human factor
that we want to remove

from the, from the situation.

As they explore their
new environment,

the wild dogs encounter

an even bigger threat
than snakes:

the one large carnivore species

that barely scraped through
the war.

(lion growling softly)

In this case, the wild dogs'
fear response kicks in.

(lions growling loudly)

Certain parts of the park
are better avoided.

Dogs don't mix with lions.

I mean, lions will kill dogs,

and so they tend to avoid lions.

(lion growls)

As fearsome as they are,

lions have not been
a strong presence

in Gorongosa until recently.

When Paola first came here
eight years ago,

the estimated lion population
was somewhere around 40.

Thanks to
a massive recovery effort,

that number has risen
to about 150.

(lion sniffing)

But even with
the lion's amazing rebound,

the fear they spread
is limited to areas

well-suited for their
ambush-style of hunting.

BOULEY: So, this is your
classicGorongosa lion habitat.

This is where lions
like to make their kills,

in this thick, tall grassland
that sits at the margin

between the floodplain
and the woodlands.

It's a perfect area
to hide and ambush prey.

So, a warthog or a waterbuck

making its wayfrom the open floodplain

into the woodlands has
topass through this tall grass.

And this is where they get
snatched by lions.

And so, it's easy prey.

They don't have to

go out into the open

and chase their prey down
for kilometers.

It's all about lying in wait,
quietly in the grass,

until their prey walk on by,
and they snatch it.

I wouldn't walk through
that grass.

You'd definitely havea
high chance of meeting a lion

in that tall grass.

Gorongosa will eventually need

several members
of the predator guild,

targeting different territory
and prey,

to get its ecosystem
back into balance.

Each predator functions

That's the beauty of it.

And so, we're missing
some of those pieces,

and those are the pieces
we're bringing back.

NARRATOR: The wild dogs don't take long to
make their presence felt.

As they expand their range,

chases and kills becomea
common sight around the park.

On average,

a pack of African wild dogs

will take down
at least two antelope a day.

(dogs chittering)

Measuring the impact
of added fear

is much trickier,

but ecologists are finding ways.

Studies covering the entire
range of the animal world,

from spiders to sharks

to house cats,

indicate that fear's influence
can be multifaceted

and include a surprising
indirect effect...

a lower birthrate among prey.

Because animals prioritize

survival over anything else,

they're going to be
looking for predators

if they think that there are
predators in the environment.

Having your head up
is highly beneficial

to keep you alive another day,

to avoid a predator attack,

but at the same time,
it carries a cost

in terms of not being able to

eat as much as you might
if the predator wasn't there,

which could then mean
that your condition suffers,

so you can't produce
as many offspring

as you could if a predator
wasn't there.

Oswald Schmitz discovered this
in his early studies.

Over time, the goldenrod-eating

living with spiders
had fewer offspring.

Grasshoppers eating grass
tended to be robust,

really good-quality eggs,

and then the grasshoppers

feeding on the goldenrod
weren't as robust.

And so, the eggs that
theyproduced were poorer in quality

than the eggs of the
grasshoppers feeding on grass.

So, there's the cost,

in terms of reproduction,
to these grasshoppers.

The African wild dogs
in Gorongosa

are certainly eating well.

The pack has its pick of prey
to feast on.

And their healthy diet pays off.

Ten months after Beira's
first litter of pups

was lost to a python,

camera traps record
the dawn of a new era.

(pups whining)

With the addition of
11 newborns,

the wild dog population
is nearly doubled.

Then a surprising development.

A second female
delivers a litter of her own,

and her eight pups
are welcomed into the pack

by Beira and raised
along with the others.

And pups in the park
just keep on coming.

Four adults split off
and form their own pack...

(pups whining)

and its alpha female delivers
another eight pups.

(pups yipping)

With these three litters,

the wild dog population of
Gorongosa has jumped

from 14 to over 40.

(dogs howling softly)

Within months, the youngsters

are joining the hunt

and the packs are carving out

their place
in the park's ecosystem.

They're making kills daily,

sometimes twice daily.

And they're feeding on species

that lions
don't typically feed on.

So, they are really
fulfilling a unique role

as a predator in this system.

I think the
most impressive thing about

wild dogs, as a species,

is the collectiveness of it.

The pack is more thanthe
individual sum of its parts.

It's like a superorganism.

Everything they do,
they do together,

and a kill is like that, too.

One animal might
take that prey down,

but within seconds, the
whole pack is on that kill,

and it's gone, done.

It's a strike zone.

Everything is consumed
and just disappears.

Even the vultures
that follow them around

hardly ever get anything.

NARRATOR: Head veterinarian Tonecas Paulo
has witnessed

clear changes in Gorongosa
since the wild dogs' release.

(speaking Portuguese):

NARRATOR: Tonecas' first-hand observations

are backed up by
the satellite data

flowing into the Pringle lab.

So, we've kind of lined up

where the wild dogs were
during that time

and where the bushbuck were
during that time

to try and see
how much overlap there was

between their spaces.

PRINGLE: They're covering this huge area.

You know, it's, it's, and,

and they're hitting all of
the major habitat types, from,

you know, this really dense
pocket of sand forest down here

to the more sort of
intermediate savanna,

you know, woodland,
all the way out

into the, you know, wide open

floodplain grasslands.

Between the areas claimed
by lions

and the home ranges established
by the wild dogs,

predators are now covering

over 1,000 square miles
of Gorongosa.

DNA analysis of wild dog feces

confirms that bushbuck
are a favorite target.

What we're getting
from the DNA and the dog scats,

it looks like bushbuck are

about half of the diet,
at least, so...

So how is that going to affect

what bushbuck eat?

We think the first thing
that happens is,

the bushbuck retreat from
the floodplain.

It's a tradeoff
between nutrition

and the risk of
being eaten yourself,

so we could expect that, yeah,

the nutrition
is going to take a hit

in exchange for
staying more safe.

(dogs yipping)

Large-scale field experiments

like this are measured in years,

but the early signs
are encouraging.

I really think that this is

the future of
environmental conservation.

If we want to have intact,

functioning wild ecosystems,

this is what we need to do.

I think what year one

is that the species
can do very well here.

They exceeded our expectations,
so that's a good sign.

It means
the system is ready for them,

and that's what we strive for.

We wouldn't be bringing in
additional packs

if we didn't feel like
we had succeeded in year one.

Tough guys?

(men speaking in background)

A year after the first

15 more wild dogs
arrive in Gorongosa,

diversifying the gene pool

and increasing the fear factor
in the park.

PAULO (speaking Portuguese):

Down the line,

the Gorongosa Project hopes

other members of its lost large
predator guild can return,

continuing one ofthe
most ambitious restorations

of this kind ever attempted.

(insects chirping)

Hyenas won't be welcomed back

until the wild dog and lion

are more stable
and better prepared

to defend themselves against
their natural enemy.

But another
iconic and essential predator

may be finding its way here
all on its own.

What is it? Over there!


Recently, a tour group
returning to camp

spotted something
just off the dirt road.

MAN (softly):
A leopard! Holy cow!

A solitary male leopard
roaming Gorongosa,

perhaps in search of a mate.

That's the first
confirmed sighting

in more than a decade,

so you can imagine the camp,
uh, feeling at that point.

Just experience it.

But it was a very special

I think it also validates
that if we protect this place,

these species come back.

But there are certain things
you have to have in place

before that can happen,

and leopard was a sign of that.

MAN (whispers):
Oh, my God!

If you give nature a chance,
it comes back.

Amazing, eh?

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