All language subtitles for NOVA.S47E13.Natures.Fear.Factor.1080p.AMZN.WEB-DL.DDP.2.0.H.264-GNOME_track3_[eng]

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.

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.

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

rare African wild dogs are
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 into
a healthy wilderness once again?

"Nature's Fear Factor."

Right now, on "NOVA."

Nature: 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 clouds
high 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 Africa
across the border to Mozambique,

and their new home:
Gorongosa National Park,

a protected wilderness on the
rebound 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 celebrated
and 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 dropped
from 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 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 reintroduction's.

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
to get some scats

while they're still in 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 signs that
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.

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.

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.

Okay.

It's really strong now.

Maybe, like, 1:00.

Okay.

It keeps coming in and out,

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

He's probably behind something.

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.

Yeah. It's super-annoying.

Sounds like he's back behind us.

Behind us again?

Yeah.

Okay, it's very
strong right 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.

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

Oh, yeah, that'll work.

Rob and Justine are rewarded
with a fresh morsel of evidence

for one of their
Gorongosa investigations...

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 the
middle of the wide-open plains.

We started calling
them "plainsbuck"

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 bushbuck

were leaving the forest,

and thought it might connect
with a much deeper issue

facing Gorongosa:

its relative lack
of large predators.

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 dinner...

perhaps the most basic
instinct in the animal world.

Until recently,
fear's role in nature

has been largely
underappreciated.

It was thought a predator's
impact 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 underestimating
the total impact that predators

might be having

out there in nature.

The successful
re-introduction of gray wolves

to Yellowstone National
Park 25 years ago

led more ecologists to attribute
another 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.

The landscape of fear is
a disarmingly simple idea

that seems to be
applying broadly.

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 reveal
the 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.

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 predator-free

feasted on nutritious grass.

But when spiders
were brought in,

the hoppers moved
up into some goldenrod,

which provided them with better
cover but less nutritious food.

Fear acted as a
kind of force field,

pushing players around the
landscape, changing the game.

When I study grasshoppers and
spiders 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 relatively small
animals that you can keep

in laboratory conditions.

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

that understanding up from
the laboratory to the real world

at the very largest scales.

And that's one of the things
we'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.

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.

But on other nights,
the leopard calls sound

intermittently through
the darkness...

Using GPS signals
from collared bushbuck,

Justine is able to remotely
witness their reactions

over the course of 48 hours.

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
center of 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 avoiding
this 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.

Other ecologists
studying fear in the wild

have run similar experiments.

Liana Zanette has used
audio cues and camera traps

to test the reactions of prey
species to predator sounds

in a South African reserve.

While bird calls are ignored...

lion growls not so much.

The odd chirpings of wild
dogs set off similar alarms.

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
something is starting there.

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?

Okay? Yes.

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

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

At this point we feel
a little stressed out,

but also excitement.

Go!

Oh, wait! Wait! Wait! Wait!

It's all about the
perception of risk.

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

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

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?

Go!

You know?

Will the pack just, like,
disintegrate and disperse

and break into smaller units?

That can happen.

- Okay...
- Okay!

Go, go, go, go, go!

♪ 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.

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 across
the river and into communities,

what kind of chaos
that can cause, right?

It's not just a
hypothetical problem.

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.

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.

When the giants
approach, alarms sound.

Rapid response teams
come to defend the crops.

Gorongosa ranger
units assist the locals,

supplying them with
tools... such as fireworks...

to help frighten the
elephants out of the fields.

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,

elephants 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.

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.

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.

Surprisingly, 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.

It turns out the surest way to
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've
extracted 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 extracted,

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.

The Pringle lab data reveal that

the bushbuck on the
floodplain are eating better than

their counterparts
in the forest.

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 separation

between who eats grass
and who eats trees and shrubs,

which is more or less
what we would expect

in a mature ecosystem
with separation of diet.

Each species got a
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
of everybody 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.

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 searching
for 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
up all 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 that she'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.

Yeah.

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.

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

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.

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.

But even with the
lion's amazing rebound,

the fear they spread
is limited to areas

well-suited for their
ambush-style of hunting.

So, this is your classic
Gorongosa 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 way from
the open floodplain

into the woodlands has to
pass 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 have a
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 differently.

That's the beauty of it.

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

and those are the pieces
we're bringing back.

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

As they expand their range,

chases and kills become a
common sight around the park.

On average,

a pack of African wild dogs

will take down at least
two antelope a day.

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 grasshoppers

living with spiders
had fewer offspring.

Grasshoppers eating
grass tended to be robust,

producing really
good-quality eggs,

and then the grasshoppers

feeding on the goldenrod
weren't as robust.

And so, the eggs that they
produced 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.

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...

and its alpha female
delivers another eight pups.

With these three litters,

the wild dog population
of Gorongosa has jumped

from 14 to over 40.

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 than the
individual sum of its parts.

It's like a super-organism.

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.

Head veterinarian Tonecas
Paulo has witnessed

clear changes in Gorongosa
since the wild dogs' release.

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.

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.

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, healthy,

functioning wild ecosystems,

this is what we need to do.

I think what year
one demonstrated

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?

A year after the
first reintroduction,

15 more wild dogs
arrive in Gorongosa,

diversifying the gene pool

and increasing the
fear factor in the park.

Down the line,

the Gorongosa Project hopes

other members of its lost
large predator guild can return,

continuing one of the
most ambitious restorations

of this kind ever attempted.

Hyenas won't be welcomed back

until the wild dog
and lion populations

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!

Shhhh!

Recently, a tour
group returning to camp

spotted something
just off the dirt road.

- 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 moment.

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.

Oh, my God!

If you give nature a
chance, it comes back.

Amazing, eh?