Original subtitles

(gentle instrumental music)

- [Narrator] This is the Luangwa Valley in Zambia.

For six months of the year,

it's a lush flood plain.

Then the heat's turned up,

and it becomes a scorching death bed,

but this dry season is going to be different from most.

(animals growling)

The sun will be the least of the problems.

There's a silent killer hiding in the shadows,

and few are safe from attack,

least of all these heavyweights.

One of the largest groups of hippos in the world

are in the front line.

They're about to face the fight of their lives.

(gentle instrumental music)

This story starts in early May.

(singing)

It's hard to believe that in just a few, short months,

this ripe valley will be a dust bowl.

(birds and insects chirping)

Deep lagoons have millions of liters of fresh water,

and the food flows freely.

(animals snorting)

The water's carpeted with thick lumps of Nile cabbage,

which these locals love.

(water sloshing)

These are halcyon days for hippos.

With no natural predators to worry about,

they spend entire days in the water keeping cool,

occasionally turning their heads to feed.

Each hippo pod averages 15 members

and operates as a free flowing social group.

In times of plenty,

rival pods respect each others' space.

(animals grunting)

Fights are few and far between.

(animals growling)

With so many pools to choose from

and a feast of food available,

neighboring groups can enjoy the good life,

but not for long.

All that's about to change.

This lagoon is home to two young bachelor males.

The youngest spends his days idly floating around,

but his elder companion keeps his chin up

and his eyes peeled.

He's older, wiser,

and always on the lookout for trouble.

(water sloshing)

Older male hippos can be far from friendly.

(birds chirping)

(wind blowing)

Nearby, a young female is getting to grips with motherhood.

Her calf's two months old,

and he was born here.

Hippos are one of the few land mammals

that give birth underwater.

Youngsters play together

under the watchful eye of other mothers.

Their support is vital.

This can be a dangerous place for a younger hippo.

(gentle instrumental music)

These lagoons stretch for many kilometers,

but they aren't the major source of water.

That lies out beyond the trees.

The Luangwa River is one of the biggest unaltered rivers

in southern Africa.

(birds chirping)

Here, a large pod of hippos live in luxury.

This is prime riverfront real estate,

(animals grunting)

but it's a fragile peace.

The first rule in any hippo household

is to know who's boss.

(water splashing)

Hippos are one of the most dangerous animals in Africa.

Adult males can weigh up to three tons,

but when the going gets tough,

they don't just throw their weight about.

Tusk like canines, which are razor sharp,

can cause carnage,

(animals growling)

and in these bruising encounters,

it helps to have a big mouth,

the bigger the jaw, the higher the ranking.

It makes sense to take the measure of an opponent

before picking a fight.

(animals growling)

(water splashing)

Most flareups are short and sharp.

It's in the best interest of the weaker competitor

to submit quickly and keep injuries to a minimum.

These power struggles are constant.

Sparring competitions between males start

when hippos are very young.

The ultimate prize is power,

(gentle instrumental music)

to be the hippo at the helm, the leader,

a bull with territory on the river,

and to have the mating rights with these beauties,

a group of up to 20 females.

The title is hard fought for.

The battle's never ending,

and the two bachelors will soon meet him head on,

but this year,

there's a far sterner test ahead

than casting out lusty rivals.

Even the toughest bull can't control the killer

that's gearing up to strike.

(dramatic instrumental music)

This enemy's been known to kill over 4,000 hippos

in a single year,

yet it's invisible, silent,

and defense is futile.

It's anthrax, one of the oldest diseases in the world

and one of the deadliest.

It's hiding down on the riverbed,

waiting for its day in the sun.

Magnified here 10,000 times,

anthrax can lie dormant for decades as spores,

waiting for the right conditions to rise

and strike again.

When most animals swallow the spores,

their days are numbered.

Spores multiply rapidly,

causing a flood of toxins which shred the immune system.

Death soon follows.

(birds chirping)

Unaware of the powder keg beneath his feet,

it's business as usual for the bull,

guarding his neighborhood.

He may even allow some young males to move in,

as long as they pay their respects first.

A drifter needs to play by the rules

if he's to stand any chance

of securing a place on the river.

(gentle instrumental music)

(water splashing)

Lowering his head in deference

is a good way to start,

and champing his jaws suggest surrender,

(animal growling)

but the bull's gaping mouth shows he wants more,

total submission.

Waving its head from side to side

and slowly paddling its tail,

the visitor finally makes the right impression.

(birds chirping)

The conditions for bachelors joining the pod are simple.

Behave submissively at all times

and refrain from any sexual behavior.

Once in a while,

a young chancer might get frisky,

forcing the bull to remind everybody

just who's in charge.

(water splashing)

(animals growling)

(gentle instrumental music)

Not only does the river provide a life giving source

of water for the hippos,

it creates a rich, fertile breeding ground.

As the flood waters spread across the plains of Luangwa,

tributaries snake away from the river.

Over time, these form separate oxbow lagoons,

home to the two males and the mother and calf.

These lakes and lagoons provide a sanctuary

for one of the most intense concentrations

of game in Africa,

but the good times are coming to an end.

The land is drying out,

and a killer will soon emerge.

(insects and birds chirping)

(gentle instrumental music)

The sun sucks the water from the valley,

and the earth turns to dust.

Conditions gain momentum for the anthrax to strike.

As the lagoons stagnate,

the disease concentrates

in the last dregs of drinking water,

and as the hot winds gather,

they whip millions of spores across the valley,

contaminating all grazing.

The thick walls of a single spore provide armor plating

for the disease,

protection against cold, heat, and drought.

All it needs is the right place to grow.

The animals of Luangwa are about to face

the toughest test of their lives.

(gentle instrumental music)

(birds calling)

(water splashing)

The bachelor coalition still feeds on the Nile cabbage,

blissfully unaware of the storm brewing on the horizon.

(animals grunting)

Nearby in the young mother's lagoon home,

there's a sinister sight.

The bloated corpse of an older female attracts attention

and provides the easiest of meals

for a passing predator.

Is this a taste of things to come?

Oblivious to the danger,

the young calf investigates the lifeless body.

His mother joins in,

dwarfed by the swollen carcass.

It's extraordinary for the calf

to be so close to these reptiles.

Crocodiles don't usually stumble across feasts like this

so early in the dry season

when there's still plenty

of food and water for the hippos.

These treats usually appear later on

when the heat's done its worst,

supplies have run out,

and starvation has set in,

but this year seems different,

and this is just the beginning.

The dry season tightens its grip.

As the sun rings the last of the water

from the lagoons

and the pools evaporate,

the hippos that have made their homes here

begin the long trek to the river,

and in so doing,

they may seal their fate.

The river's no sanctuary.

It's a death zone.

The water level is already dropping,

creating perfect conditions

for the anthrax to attack.

The low levels force the hippos to wade into the middle

where the water is deepest.

In these congested conditions,

their heavy stalking stirs up the riverbed

and releases millions of deadly anthrax spores

straight into their drinking supply.

Spores gain access to the hippos' tissue

through open wounds or on route to their stomachs.

(gentle instrumental music)

Once in the body,

the spores soon germinate,

forming rapidly dividing cells

and a mass of deadly toxins.

(birds and insects chirping)

Zero hour has arrived.

(animals grunting)

The carnage has begun.

The water the hippos are so desperate to drink

is their downfall,

every mouthful a potential death sentence.

With every passing day it gets worse

as the river fills with more swollen carcasses.

For crocodiles, it's paradise,

an effortless supply of meat without the hassle of hunting.

When reptiles shred corpses

and blowflies feast on open wounds,

they help the disease spread.

(insects buzzing)

As soon as a carcass is punctured,

exposure to the air triggers the anthrax

to form spores.

(dramatic instrumental music)

The plague's now free to launch an airborne assault.

(birds chirping)

As the water level continues to drop,

the anthrax becomes even more concentrated.

(animals grunting)

Millions of the microscopic spores,

small enough to fit on a pinhead,

wait to be sucked up,

gulped down, and go to work,

(gentle instrumental music)

but it's not just the hippos who are affected.

Many other inhabitants of the Luangwa Valley

will lose the war.

Natural instincts are put to one side

in the desperation to drink.

The shrinking river forces predator and prey

into uncomfortably close contact.

The situation's getting worse.

In the height of the Zambian dry season,

some relief can be found

from the aptly named sausage trees,

which dominate the river banks.

Many of the valley's animals feed

on their distinctive fruit, leaves, and flowers.

The fleshy fruits are crammed with nutrients.

It's manna from heaven.

In a severe drought year,

they can make the difference between life and death,

but this year, they won't be enough.

(gentle instrumental music)

(wind blowing)

As the dry season advances,

the lagoons either side of the river are transformed.

Scrappy clumps of river cabbage remain,

but water is at a premium,

and the hippos are suffering more than most.

(birds and insects chirping)

Antelopes can nimbly negotiate the mud.

Baboons can flit across the hippos' leftovers,

but for heavier animals,

the going is painfully slow.

Desperately searching for water,

a buffalo is up to its neck in trouble.

It might have escaped the anthrax,

but caught in the grip

of the thick, cloying mud,

it faces a slow and agonizing death.

The majority of the hippos

have already left for the river.

Most marched on less,

but some struggled to keep up with the rank and file.

Amongst the stragglers,

now hours behind the rest of their pod,

are the mother and calf.

Still young and weak,

the calf is much slower than its mother,

but she lets her son set the pace

and follows dutifully behind.

(birds chirping)

Water is their only hope of respite

from the relentless heat of the sun.

They have some natural protection.

Their skin secretes a viscous red fluid

which blocks ultraviolet light,

acting like a sunscreen,

but it won't last forever.

They must find water or shade as soon as possible.

(gentle instrumental music)

Despite the appalling conditions,

not all the hippos have left.

The youngest male is staying put.

All the cabbage has gone.

He hasn't eaten in days,

but still he seems reluctant to leave.

His older companion waits nearby.

With three dry seasons under his belt,

his instincts are to leave for the river,

but he seems determined

that they will make the journey together.

The situation can only get worse.

Like the elephants,

they need to head for the river.

Eventually, either his perseverance

or his friend's hunger reaps rewards.

They begin their journey side by side.

(animals calling)

It's day 22 of the anthrax outbreak,

and today the mother and calf finally arrive at the river.

Their presence attract a lot of curious glances.

(animals grunting)

The river bull watches nonchalantly.

He seems unconcerned.

A young mother and calf returning to his territory

are no threat.

(birds chirping)

(water sloshing)

As the youngster tests the water,

his peers size him up.

Both mother and calf are desperately dehydrated.

Now at last they can drink,

(animal grunting)

and it might be one of the last things they do.

(gentle instrumental music)

For the resident bull,

the mass exodus of hippos from the lagoons

to his stretch of river is a mixed blessing.

The procession of new females trudging through his territory

is a good thing,

but the stream of males who travel in their wake

are far from it.

(animals grunting)

(singing)

More males would normally mean

more challengers to his throne,

(water sloshing)

but this year is no normal year.

The hippos are dying,

newcomers and pod members alike.

(birds chirping)

The epidemic is spreading.

The lifeless body of another anthrax victim

attract attention,

and not just from the crocodiles.

(animals grunting)

Despite the presence of predators,

the death of one of their own

seems to be an irresistible draw

and a source of fascination to other hippos.

(gentle instrumental music)

Most mammals show little interest

in the death of their kind,

but elephants and chimps have both been shown

to have an understanding of mortality.

The reason for this young male's strange behavior

remains a mystery.

(insects buzzing)

(animals grunting)

The river bull doesn't seem interested in the corpse.

He's more interested in the mourner.

The inquisitive young male has aroused his suspicion

and his hackles.

The new arrival is no match for the reigning leader.

The best he can muster is one feeble gesture of defiance.

The bull's reply is short, sweet,

and rammed home with gaping jaws,

(animals growling)

and the battle's over before it's begun.

(gentle instrumental music)

(water sloshing)

Despite having ringside seats,

this audience is otherwise engaged and engorged.

Day 31, and the dead are now as big a feature

of the riverbanks as the living.

Over 50 have already perished.

Anthrax works at breathtaking speed.

Every day more members of the pod

are found dead,

many without having shown any outward signs of sickness.

(birds cawing)

Whether it enters through open cuts

or is ingested,

the disease races through the body,

penetrating, paralyzing,

and killing cells,

decimating defense systems,

and causing fatal hemorrhaging.

(gentle instrumental music)

(animals grunting)

As the sun sets on another gruesome day,

the survivors settle down for the evening.

(water splashing)

(singing)

After a day of fending off aggressive young males,

the river bull can finally turn his attention

to the females in his territory.

Mating takes place underwater

where the bull will mount a female in estrus.

A short way downstream,

the mother and calf relax,

strengthening their bond with some gentle nuzzling.

(gentle instrumental music)

(birds chirping)

As night falls, the hippos leave the river to graze.

(water sloshing)

Ideally, hippos remain in the river most of the day.

Excessive water lost through their skin

means they can easily dehydrate in the heat,

so they normally leave the river

to feed on land during the cooler hours after dark.

(insects chirping)

They can travel up to 10 kilometers in search of food,

and when they find it may graze

for as long as five hours.

Feeding is fast and furious.

Hippos can consume about 40 kilograms of grass per night,

though that's a mere 1.5% of their body weight,

but being away from the water

doesn't mean they've escaped the dangers of anthrax.

Cropping the grass very low

means they ingest anthrax spores from the soil.

(insects chirping)

(gentle instrumental music)

The two bachelor companions are still searching

for a safe haven.

They've spent another long day tramping

in the blistering heat

with barely a drop of water.

The fruits of a sausage tree offer some respite,

but is it too little too late?

Desperate for more food and water,

they are fraught and frail.

It hasn't gone unnoticed.

Lions and hyenas would think twice

about attacking a healthy adult hippo,

but they might take a chance on a weak one or two.

Another day without water

could spell disaster for the two hippos.

(animals calling)

(gentle instrumental music)

It's day 40 of the outbreak.

At last the two comrades appear to have found a new home,

but the dominant bull is watching them.

Can they survive where so many others have perished?

(animals grunting)

The prospect of water and food propels them

towards the river

and straight into danger.

(animals grunting)

If they're rumbled by the river bull,

they're in big trouble.

They're far too weak

to get dragged into a leadership contest.

Gingerly approaching the water,

their only hope is to try and slip in unnoticed

at the side of the river,

(birds chirping)

but covert moves can prove tricky

with a three ton frame to disguise.

(water sloshing)

The older male plays a skillful game of bluff,

settling into the water

like he's an existing member of the pod.

The bull seems to accept him,

but his younger companion is far less convincing an actor.

(dramatic instrumental music)

With their cover blown,

the youngster tries to remedy matters

with a desperate show of submission,

but the bull's already committed

to his course of action,

instant expulsion.

Every supportive, the older hippo rushes in

to help his young comrade,

(water splashing)

but the bull's taking on all comers.

He makes it crystal clear

they need to leave his stretch of river.

(animals grunting)

(birds chirping)

(gentle instrumental music)

The older hippo has no stomach for a fight,

and the battle's over before it's begun

without a single drop of blood spilt.

(animals growling)

(water splashing)

For the resident bull,

it's another successful eviction,

but for the bachelors,

it's back to wandering.

These hobbling hobos still have no home,

but being banished from this part of the river

might prove to be a blessing in disguise.

(gentle instrumental music)

The river is still teeming with anthrax spores,

ready and waiting to attack the next victims,

but the two hippos are still in dire straits.

Their only hope now is to find any available water,

hunker down, and wait for the rainy season.

(birds chirping)

It's now day 45 of the anthrax outbreak,

and with each passing day,

the fatalities mount up.

Space is at a premium.

Tempers are strained,

and fights open more wounds to welcome the anthrax.

It's the final factor making this dry season

especially dire for the hippos.

A combination of limited resources

and the resulting stress from overcrowding

seriously hampers the hippo's immune system,

making them less able to fend off infection

and ever more susceptible to disease,

but not everyone's suffering,

far from it.

Hippo hell is crocodile heaven.

For these writhing reptiles,

it's been a season to die for.

The food just keeps on coming,

and they've no need to waste their energy killing it.

Just paddle up and eat.

Grisly it may be,

but as they devour the latest victim,

their performing a vital role in the ecosystem,

keeping the riverbanks clean.

Crocodiles have been around for millennia

and are immune to the disease.

They have the most acidic digestive system

of any animal

and are coldblooded to the core,

which tips the scales in their favor.

The anthrax might have met its match in the crocodiles.

(birds chirping)

(gentle instrumental music)

Despite the wave of deaths,

the river bull still maintains control of his patch.

The mother and her calf may have found

a new home with his pod,

but it's a poisoned chalice.

The luckiest ones may be those

the river bull sent packing

away from this part of the river.

The two males may have avoided contamination,

but life is a grueling struggle.

Theirs is a punishing quest to find somewhere

to cool their desperately overheating bodies,

but they search in vain.

Most of the pools have evaporated.

There's not a drop of water in sight.

It's exhausting,

and eventually in the searing heat

they reach breaking point.

Tempers fray and finally snap.

(animals growling)

Their bond is broken.

From now on, it's every hippo for himself.

(birds and insects chirping)

(gentle instrumental music)

It's now 50 days since the anthrax

claimed its first victim.

Its latest leaves an orphan in its wake.

The calf waits patiently by his mother's corpse.

(singing)

(water sloshing)

Only five months old,

he's young to be without her guidance.

A mother and calf would normally stay together

for up to eight years,

but at least the youngster is weaned,

which gives him a fighting chance,

(animals grunting)

and she found him a support network,

a place in a creche where there are other females

to care for him.

The pod may be depleted,

but the community of mothers

caring for an extended family

is still its backbone.

His mother did all she could.

Now he must take his chances in the battle

against the deadly disease raging in the river.

(birds cawing)

A scavenger swoops,

signaling another death.

The epidemic is spreading.

(dramatic instrumental music)

This time, it's not a hippo festering in the mud.

Anthrax is now affecting almost everything in its path,

bar the cleaners who mop up the dead.

(birds squawking)

Like hippos, buffaloes are more susceptible to anthrax.

They wade into danger,

heading deep into the river

and stirring up trouble,

the disease rich sediment beneath them.

The feathered clean up crew are still on duty.

They're specialists,

slicing bodies open, removing entrails,

and shoveling down flesh at great speed.

They're also unwitting experts

at spreading disease.

This freshly butchered carcass is riddled with anthrax

and highly contagious.

Like crocodiles, vultures have got the guts for this job.

They're resistant to the disease.

Infected meat passes straight through

their highly acidic stomachs,

but after supper when they drink and bathe,

they contaminate the surrounding water

for the other animals.

(gentle instrumental music)

Vultures aren't the only creatures peddling pestilence.

Blowflies perform a similar disservice.

(insects buzzing)

They swarm on carcasses to gorge

on the bodily fluids and rotting flesh,

all of which is riddled with disease.

When they fly off and land on nearby vegetation,

they vomit and defecate droplets laced

with the lethal bacteria,

making the disease accessible

to a far loftier audience

and many other grazers besides

with lethal consequences.

(gentle instrumental music)

Day 80,

the vultures guzzle another victim,

and this time, they've got an audience.

(birds squawking)

The younger bachelor has stumbled across the carnage,

and he seems intrigued.

As long as he watches from a distance,

he's safer, but curiosity drives him closer.

He ignores the vultures

and investigates the grim scene

up close and very personal.

The reasons behind this strange fascination

with the death of another species

are shrouded in mystery,

but the effects of getting so close

to the corpse of an anthrax victim

may soon become crystal clear.

Three hours later,

despite their squabble,

the companions have reunited

and stumbled across a sanctuary of sorts.

(gentle instrumental music)

It's a far from sumptuous pool,

but this parched mud hole

would at least bring some relief,

but a wallow in the sludge

is as good as it's going to get.

(mud sloshing)

For one of them,

the tide's about to turn.

Anthrax is an enigma.

Resistance is different for each and every animal.

Death can take a few days or a few hours,

and some can even survive the disease,

(insects and birds chirping)

(gentle instrumental music)

but not in the younger hippo's case.

He lasted mere hours,

his crumpled body now easy pickings for night prowlers.

With their cast iron stomachs,

the hyenas appear to be impervious to infection,

(animals chewing)

but the older hippo isn't.

Helpless in the background,

he can only watch,

but it's a dangerous preoccupation.

Every minute the young hippo's body

lies open to the elements,

the more anthrax seeps from his wounds

into the watery silt

and slowly weaves its way

towards his elder companion.

(water sloshing)

(gentle instrumental music)

(birds and insects chirping)

By morning, the water hole is a hive of activity

as parched residents struggle

to find somewhere to quench their thirst,

but the water's rank and stagnant,

concentrating the anthrax

and making the situation even worse.

(hogs snorting)

To some degree,

most mammals are susceptible to anthrax.

The chances of falling prey depend on specific temperature

and humidity conditions within the host's body.

Survival is a lottery, a numbers game,

one which the older hippo seems to be winning so far.

He made it through the night,

but every hour spent in the sludge

alongside his comrade's remains

severely reduces his chances.

Even if he survives the anthrax,

the heat is relentless,

and this meager spattering of water won't last long.

(insects chirping)

(water sloshing)

At the river,

the calf is still with his mother.

She has been dead for two days now.

If he's to survive,

he must give up his vigil.

(gentle instrumental music)

His attempts to push the crocodiles away are futile.

With so much food on offer,

the reptiles ignore him.

At least the youngster is still alive.

He must now use whatever strength he has left

to continue bonding with other females in the river.

(water sloshing)

(birds chirping)

(gentle instrumental music)

(insects chirping)

Back at the mud hole,

the older hippo is also moving on.

He's been lucky to withstand the anthrax,

but if he's to have any chance of longterm survival,

he needs to return to the river,

but he won't be welcomed back.

The river bull will still be on patrol

and ferociously guarding his empire.

This frazzled giant has one more challenge to overcome,

and it's a monumental one.

(insects buzzing)

The bull takes stock.

It's been exhausting maintaining his territory,

but his work isn't over yet.

The wanderer returns,

but this time, he's not trying to slip in

through the back door,

quite the opposite.

His eyes seem fixed on the main prize.

The lines are drawn,

and there's no backing down.

(dramatic instrumental music)

When a fight this brutal is brewing,

no one wants to get caught in the crossfire.

(animals grunting)

(water splashing)

(animals growling)

In a blistering brawl of clashing canines

and bone crunching jaws,

two Goliaths go to war.

(birds chirping)

The opponents are evenly matched.

The bachelor male equals the bull kilo for kilo,

and what he lacks in combat experience,

he makes up for in youthful energy.

Despite his recent ordeal,

the young contender has the upper hand.

(water sloshing)

The river bull has fought one too many fights.

His battle weary body isn't up

to another punishing contest.

His 10 year reign is over.

This stretch of river has a new head honcho.

This victor survived the heat,

starvation, and the onslaught of anthrax.

Now he has power and his own territory on the river.

(gentle instrumental music)

The vanquished leader can barely muster the energy

to lick his wounds.

(birds chirping)

Bleeding and battered,

death will come quickly.

(insects buzzing)

After 140 days,

there's hope on the horizon.

The rain clouds gather,

(thunder rumbling)

and the plague is gradually purged

by the torrential downpour.

(rain pouring)

(water flowing)

As the river swells,

the spores are washed away.

The anthrax, diluted in the deluge,

is no longer a threat.

(birds chirping)

(singing)

Hippos have two basic requirements for life,

water deep enough to wallow in

and grasslands fit to graze.

The lethal combination of a savage dry season

and the ensuing anthrax outbreak

almost destroyed these basic resources.

(water splashing)

Almost, but not quite.

For the survivors,

it's the beginning of a new era.

The ordeal which killed so many

brought a new lease of life for others.

(birds chirping)

The older bachelor now reigns supreme in his territory.

He's inherited a huge pod,

including within its ranks the young orphan,

now safely ensconced in the group.

His mother saw him safely to the river

and made sure he'd never be alone,

that he'd always be under the watchful eye

of the sisterhood.

Without their support,

it would be a very different story.

(water splashing)

The pod may stay here for many years,

their lives revolving around the ever changing face

of the river and its surrounding lakes and lagoons.

Beneath their feet, buried in the riverbed,

the silent killer bides its time.

A severe anthrax outbreak is unlikely to strike again

for another 10 years

because the pod's diminished numbers

will lessen the stressful overcrowding.

(singing)

This community has endured one of the toughest dry seasons

they're ever likely to know,

but life will go on for the survivors

of Luangwa's hippo hell.

(upbeat instrumental music)