Original subtitles

Namibia,

Southern Africa.

A vast, dried-up lakebed...

..where temperatures can reach

almost 50 degrees Celsius.

Overheating

is dangerous for all.

Nonetheless, in this cauldron of heat...

..mammals have found a way to survive.

Across the planet,

mammals have learnt how to deal with heat...

..in the most remarkable ways.

The Serra da Capivara in Brazil.

A world of harsh, dry forest...

..and scorched cliff faces.

Here, the dry season lasts

for up to seven months.

And what little rain that falls

quickly disappears.

Despite this,

one mammal has made it home.

A family of bearded capuchins.

They have spent the night

high up on the cliff faces,

safe from any predators below.

It may be early,

but already temperatures are beginning to soar.

The troop

needs to find water.

And none need it more

than a mother.

Without it,

she won't be able to produce the milk

essential for her young baby.

But first, they must make the treacherous journey

down to the forest floor.

The newborn must hold on tight.

Others forge ahead.

For the first to reach the forest floor...

..the last few cashew fruit

provide some welcome sustenance.

But there's not enough to go around.

Mother and baby must go without.

At nearly 40 degrees,

the heat is relentless.

Desperate,

the troop look for anything

that might contain water.

Could the trees provide the solution?

Hidden in some trunks,

there is a little water,

left over from the last rains.

But reaching it

is a real monkey puzzle.

Mammals, however,

are experts at solving problems.

An older male tries a different approach.

Perhaps a bit more brains

and a little less brawn.

A stick produces a dribble of success.

Having watched all the others try,

the mother finally gets her turn.

Her tail acts like a sponge...

..soaking up any water

that has collected in the trunk.

Being able to tap these hidden wells

is more than just a clever trick.

It's a life-saving lesson...

..and one the rest of her family quickly learn.

Their ability to solve such problems

will help the troop survive

these long, hot, dry months.

And, finally, the newborn

can get a much-needed drink of its own.

But there are places

that are even hotter and even drier.

Australia -

the driest inhabited continent on Earth,

with almost a million square miles of desert.

A furnace where water is almost impossible to find.

An Arabian camel.

Introduced in the 1800s by early explorers,

it's estimated that as many as one million

now roam the outback.

For this lone male in search of a mate,

desert plants

provide a few slim pickings.

Any surplus nutrients

can be stored in his most famous feature...

..his hump.

Full of fat,

it's a built-in energy store

that can be tapped when needed.

And as long as he can find food,

he can go without drinking for months.

At last,

what he's been looking for.

A herd of females.

It's important

that he makes a good first impression.

And he has a special way of doing so...

..with a dulla.

This inflatable sac

is unique to camels,

and accompanied by loud gurgling...

..is his way of attracting females.

Has he done enough to impress?

Apparently not.

A raised tail is a polite way of saying,

"No, thank you."

Not so easy after all.

Could she be the one?

Looking good!

Bad luck, Romeo.

Despite his best efforts,

it's not been his day.

Camels have overcome

the desert's greatest test -

its lack of water.

But this is not the only challenge

faced by mammals

in hot and arid conditions.

Just as dangerous

is the risk of overheating.

Sifaka lemurs...

..in one of the hottest

and driest places in Madagascar.

The trees provide some shade...

..and a little relief from the burning sun.

But with midday temperatures

that can exceed 45 degrees...

..the heat up here soon becomes unbearable...

..especially for the babies...

..the most vulnerable members of the group.

But sifaka

have an unusual and clever way

to cool down...

..if only they can find the right tree.

And once they have...

..they hug it.

The Salvadora tree

is one of their favourites.

These trees draw up cool water

from deep below ground...

..so their trunks are a few degrees cooler

than everything else around.

At the hottest time of day,

some embraces can last for over four hours.

And some trees are so popular...

..there isn't an inch to spare.

This remarkable behaviour

was first recorded by scientists in 2017.

As the world becomes hotter,

we may see cooling behaviours like this

become more and more common.

But some sifakas have gone one stage further.

They know the best place

is within the trunk

of the Salvadora tree.

Here, the temperature can be even cooler.

And that can give real respite

from the oven outside.

Sifakas have learnt that tree-hugging

is an effective way to keep cool.

But some mammals

face a far more dangerous source of heat than the sun.

The dry eucalyptus forests of Australia.

Home to one of the most bizarre of all mammals.

An echidna.

It's one of the most ancient of mammals

and reproduces

by laying eggs.

She's out foraging,

using her highly sensitive nose

to look for ants and termites.

To work at its best,

her nose has to be kept moist.

And this has led her

to developing an unusual skill.

She blows snot bubbles.

As the moisture evaporates,

it helps to cool her down.

But this female is not alone.

She can be followed

by up to ten or more males...

..all vying for her attention.

It's what is known

as a love train.

And it can run for weeks.

One male has managed to get close.

With such a prickly partner,

a gentle touch is needed.

But some romantic liaisons

don't last long.

With their sensitive noses,

echidnas can detect

the early signs of danger.

A bushfire.

Their best chance of safety

is to get underground.

Echidnas often go underground

to avoid the severe heat of the day.

But they also have to do so

to escape the heat of a bushfire.

Between 2019 and 2020,

Australia experienced

its most catastrophic bushfire season on record.

Over 100,000 square miles,

an area larger than the United Kingdom,

was devastated.

But in such dangerous conditions,

echidna have a remarkable survival skill.

They go into a deep sleep

known as a torpor.

It's a form of hibernation,

during which their heart rate

may slow to only four beats a minute.

Their core body temperature drops.

And they may only take a breath

once every three minutes.

By doing this,

they can live for days without food or water.

After the fire has passed...

..the echidnas begin to emerge.

Not all are unscathed.

Melted spines

show that this one

has had a close call.

But others

show no ill effects.

Their unique adaptations

have kept them safe.

But as global temperatures rise,

forest fires are becoming more intense...

..and more frequent.

The survival skills of echidnas

will become even more crucial.

Going underground to avoid the heat

makes obvious sense,

but one mammal

does the exact opposite.

Harris's antelope squirrel.

Even during the height of summer,

when ground temperatures

can exceed 80 degrees Celsius...

..he will be out foraging

amongst the cactus of the Arizona desert.

By being out now,

he avoids competition from other mammals.

But the squirrels don't have it all their own way.

A rattlesnake,

which is looking for

a rodent-sized meal.

It's a stand-off...

..to see who can withstand

the most heat.

As the ground temperature continues to rise,

the squirrel's core temperature

reaches 43 degrees Celsius.

That would be fatal for humans

and most other animals.

But the squirrels have a clever trick

that can quickly reduce their body temperature.

He heat-dumps.

By spreading its hot body

against the cooler sand in the shade,

a squirrel can rapidly reduce

its body temperature down

by up to one degree a minute.

The rattlesnake simply can't compete.

It has to find shelter

to avoid overheating.

With the coast now clear,

the squirrel can continue his search

for the fruit of the spiny cholla cactus.

But this one

has already lost all of its low-hanging fruit.

There's only one thing for it.

He will have to clamber up

the spine-covered branches.

He must be very cautious.

But this fruit...

..is a stretch...

..too...far.

Try again.

But the price of success

can be painful.

He has to remove

some very sharp spines.

A final heat-dump

before enjoying the fruit

of his labour.

This tiny squirrel

has found a clever way to deal with the heat.

But when you're nearly six metres tall

and weigh almost two tonnes...

..it's altogether a much bigger problem.

The Hoanib Valley

on Namibia's Skeleton Coast.

Home to some of nature's real giants.

Giraffes.

This herd is guarded by a dominant bull.

They spend much of their day out in the open,

searching for food.

Their tongues are black

with a pigment that acts as a sunblock.

But this is only one of the ways

by which a giraffe beats the heat.

It's now about to use

another of its heat-beating adaptations.

A rival male.

He approaches the females.

The dominant bull moves to intercept.

The bulls square up.

These blows are violent enough

to tear skin and break bone.

They're now pushing themselves to the limit.

Their core temperatures

are rising to near-lethal levels.

The reason they don't overheat

is connected to their distinctive skin pattern.

A thermal camera reveals

that below each brown spot

there is a dense network of blood vessels.

As the giraffes' body temperatures rise...

..these blood vessels expand...

..releasing body heat...

..so enabling them to fight on.

The force of each blow

is visible as a white-hot slash.

The dominant bull wins...

..and his rival retreats.

In Trinidad lives a mammal

that detects the heat that animals produce...

..and uses it to guide them

to a drink of their victim's blood.

The white-winged vampire bat.

On the prowl

for its next victim.

This cockerel is fast asleep.

But the bat must be careful.

Cockerels are light sleepers.

The bite must be delivered

with precision.

Heat-sensitive receptors

enable vampire bats

to detect subtle differences

in temperature...

..so it can pinpoint exactly

where the warm blood flows close to the skin.

She bites.

Her saliva contains a powerful anticoagulant

known as draculin.

It ensures that the blood

continues to flow freely.

This helps her feed quickly

and avoids her being noticed.

But blood isn't, in fact, very nutritious,

so the bats have to drink

over half their own body weight

in one sitting.

As a result,

flight becomes nearly impossible.

But her kidneys are remarkable...

..and quickly extract the water from her meal.

So, within minutes,

she vanishes into the darkness...

..leaving the cockerel none the wiser.

While vampire bats use heat

from the blood of their victims to find their meals,

one mammal uses the heat from the sun.

Uganda, in Africa,

on the banks of the River Nile.

A troop of baboons has gathered

at the end of the long, hot dry season.

They are waiting

for a very special seasonal opportunity.

It begins

with the annual emergence of flying termites.

They provide the baboons

with a small but much-needed treat.

But the older members of the troop

know there is another delicacy to be found here...

..one that provides them

with a far more nourishing meal.

A Nile crocodile.

She laid her eggs...

..in the warm sand.

The baboons would steal them if they could.

But the crocodile,

weighing nearly a quarter of a ton,

is one of Africa's most formidable predators

and well able to kill a baboon...

..so the utmost caution is required.

Their plan is simple.

They wait.

Whilst the crocodile must stay in the sun,

guarding its nest...

..the baboons keep their cool in the shade...

..waiting for just the right moment.

The crocodile begins to gape.

It's a way of losing heat.

The sun

gets stronger.

But the crocodile stays on guard

and risks overheating.

Eventually, it gets so hot...

..that it takes to the water to cool down.

But the baboons still do...

..nothing.

Their waiting game has not yet finished.

There's no sense

in overexerting yourself in the heat...

..when you can let hungry monitor lizards

do the hard work.

Finally,

the moment they have been waiting for.

Now they need to move fast.

The crocodile won't be away for long.

The oppressive heat

has allowed the baboons to get the food they want.

But there are few places in Africa

where the battle to find food

is more demanding

than the Etosha salt pan in Namibia.

As temperatures rise across this vast wilderness,

mammals of many kinds

are gathering around a shrinking water hole.

For a female jackal...

..this is a good place to hunt.

But it's almost too crowded.

For a jackal to be successful,

it needs to be clever.

Just a ghost

in the background.

Some of the largest mammals on Earth

dominate the water's edge.

The jackal must bide her time.

She spots possible prey.

Guinea fowl.

Thirst, however,

dominates everything else.

And hunters and hunted

drink alongside one another.

Temperatures are still rising.

The drinkers start to quarrel...

..and she retreats.

But then...

..things get even more difficult.

A hyena.

More than capable

of killing a jackal.

But driven by hunger and thirst...

..this female holds her ground...

..and now can get back to hunting.

This time, she sets her sights

on a flock of doves...

..and tries a more subtle approach.

Hiding in plain sight.

Lulling the birds

into a false sense of security.

She waits for the perfect moment.

But they aren't so easily caught.

Nonetheless...

..she's determined.

Success at last.

Her mate arrives...

..and he has brought their hungry pups with him.

With so many mouths to feed...

..she will have to be hunting again soon.

Mammals have an extraordinary ability

to find water...

..stay cool...

..and use heat

to their advantage.

That has enabled them to flourish

in some of the harshest and hottest environments

on the planet.

But if the world is indeed to become even hotter,

as is predicted...

..then the challenges facing mammals

will become greater than they have ever been.

In Madagascar,

the Mammals team hoped to be the first to film

some recently discovered behaviour...

..sifaka lemurs tree-hugging.

But to get there,

it's a three-day drive over rough terrain.

A little too much for producer Rob Pilley.

Happy to be back on terra firma,

the team set off on foot

through the spiny forest.

They've joined forces

with local scientists

from the ESSA research group.

And thanks to their expertise,

it doesn't take long to find the sifaka.

They're a little wary of humans,

so we have to go really slowly, approach them slowly.

They're quite skittish.

The sifaka are much more nimble

moving through the forest

than the crew carrying bulky kit.

Keeping up with the troop

is not without its snags.

Ah, everything is out to get you,

it's just this giant cactus forest.

They are everywhere, the spines.

And the dense scrub

makes getting any shots a challenge.

Yeah, it kind of makes you almost forced to shoot

such high-angle shots when it's so dense

cos we can't get further back.

Also just manoeuvring around the forest,

it's pretty hectic.

Trying to go quietly without snagging your camera

or your lens or a cable or...

..is, uh, not easy.

Over the following days,

the team struggle through the heat,

with the lemurs giving them the run-around.

We just found a group and they've just disappeared off.

This is going to be a marathon, not a sprint.

Lemurs Behaving Badly!

As temperatures rise,

the lemurs finally seem to settle.

This could be a breakthrough for the team.

Stu is up front.

It's just possible

that we have found

the perfect tree-hugging group.

Fingers crossed.

Not this time.

Just been given the run-around all morning by these lemurs -

starburst, every direction.

Couldn't get a single shot.

It's like the worst day ever!

Back at camp,

it's 45 degrees in the shade.

While Stuart finds a way to cool himself off...

Whew! That's good!

..Jeandre is more worried about the equipment.

We raised the laptop up on these hard drives

to give it some cooling. It's just too hot.

The cameras are melting.

The little metal pins in the camera

have literally melted. It's...

I've never had that on a shoot.

Despite the heat,

the team are forced to work

during the hottest part of the day

if they want to film

this unique tree-hugging behaviour.

But as the lemurs lead them deeper into the forest,

they notice something is amiss.

In the heart of this protected area,

there are signs that trees have been felled.

We see for the last two, three years

increasing cutting within the forest

and we believe that it's because

these people are so desperate

and cut the trees for the forage for their animals

and then for their daily needs.

With ongoing drought,

crops are failing,

and local people are forced

to turn to the forest to make ends meet.

Across Madagascar,

deforestation and the effects of climate change

are only making life harder

for both wildlife and people.

It's a sobering reminder to the team

of the problems faced by these lemurs,

who are having to adapt to a rapidly changing world.

Back on the trail,

the team split up to cover more ground.

Now separated,

the researchers have a special way to keep in touch.

Using calls similar to the animals

lets them maintain a low profile.

But as they push forward,

the heat of the day

is taking its toll on Jeandre and Rob.

We...we all just have to stop for a bit,

have a breather.

And when they start moving again,

they quickly realise they're lost.

It all looks the same.

I think it's up here.

We're not really quite sure...

..where we are.

Ow!

In these conditions,

it only takes a few hours for heatstroke to set in.

Yeah, OK, they're ahead, they're ahead. That's good.

There's a friendly face!

So nice to see you.

Somebody wandered off that way...

Quickly, things can go really pear-shaped

unless you're on your game, so...

A lesson learned, definitely.

Despite this close call,

the team are determined to continue.

It's the hottest day so far,

which should work in their favour.

At last,

they find a group that is settling.

Lemurs only tree-hug in the hottest conditions.

All the crew can do now is wait.

Finally...

..what they came for.

Thanks to the work of this research team,

the efforts to protect the sifakas' home

will continue.

With the education

and working together at different levels,

from locals to national,

to international levels,

for common goals,

then I be very optimistic, the future of Madagascar.

Next time...

..forests, where we

discover how nearly three quarters of all mammal species

have made their home in this,

the richest and most diverse habitat...

..on Earth.

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