All language subtitles for The Life of Mammals 1of9 A Winning Design 720p HDTV x264 AAC MVGroup org_Subtitles01.ENG

This is one of the coldest places
on Earth - the high Arctic.

Here, the temperature drops
to 50 degrees below freezing.

If I didn't have
all this specialist clothing on,
the cold would kill me in minutes

and yet there are animals
that live here all the time.

And one of the most remarkable
is hunting just over there.

An arctic fox.

The only reason
that it and I don't freeze solid
is that we're both mammals,

and have the mammal's ability
to use our food to heat our bodies.
We're warm-blooded.

The reason that it is more at home
up here than I am

is it has more of another mammalian
characteristic, hair, than I have.

Its body is insulated with fur.

Warm-bloodedness is one of
the key factors that have enabled
mammals to conquer the Earth,

and to develop the most complex
bodies in the whole animal kingdom.

In this series, we will travel the
world to discover just how varied
and how astonishing mammals are.

We go to Africa - where the mammals
are at their most spectacular.

Here the plains are thronged

with specialist grass eaters.

And there are other mammals here
too, with different tastes.

Some hunting mammals have become
the fastest creatures on Earth...

..and those they hunt
have had to respond or die.

Some mammals have become
fearsomely strong and aggressive.

They fight for mates.

They fight for food.

Some even have to fight
for a place to live.

Wherever you go, you find
a bewildering variety of mammals.

Some are miniatures -

a few inches long.

Others are massive.

And the biggest of those on land
are dwarfed by those in the sea.

I can see its tail -

just under my boat here.
And it's coming up.

There! The blue whale!

It's the biggest creature
that has EVER existed on the planet.

Mammals are as at home in the water

as they are on land.

Some lounge around on the surface...

..others prefer to do so
on the beach.

We will go underground
to track them,

and up into the tops
of the tallest trees.

Mammals have even taken to the air
and challenged the birds.

In some places, they congregate
in astronomical numbers.
They thrive almost everywhere.

And how they do so depends,
as does so much in the life
of mammals, on what they eat.

Between them, they tackle
everything that's edible.

Some are very particular
about their food.

Others will simply take the best
of whatever's around at the time.

On top of the menu, right now,
is salmon.

We will look at the lives
of our closest relatives...

LAUGHS

..and they will lead us
to ourselves...

..perhaps,
the most successful variation

of the mammal's winning design.

To catch a glimpse of the very
beginnings of the mammalian dynasty,
we must travel to Australia.

I'm looking for one
of the most ancient of all mammals.

It's so ancient, it shares at least
one characteristic with reptiles.

It's a very elusive creature,
but here, in South Australia,

there's a population that have been
fitted with radio transmitters, and
I can track them with this aerial.

And I've got a very strong signal.

At first glance,
you might think that this mammal
is some sort of hedgehog

or perhaps a porcupine,

but actually it's weirdly different

from a hedgehog, a porcupine
or almost any other kind of mammal.

It's an echidna.

And you can tell that it's a mammal
because it's got hair.

And only mammals have hair.

Indeed, some of its hairs
have been enlarged and strengthened

and then turned into big spines,

which give it
such an effective armour.

This hair
helps to keep the echidna warm,

making sure that it doesn't lose
valuable body heat to the cold air.

The fuel with which the echidna
and every other mammal generates
that heat is, of course, food.

On a cold winter's day like this,
the echidna spends most of its time
searching for its next meal.

Although echidnas have
good eyesight and excellent hearing,

it's their sense of smell
which guides them to food.

They sniff out insects and grubs,

and get at them by ripping open the
nests and tunnels with their claws.

That beak-like snout
pokes into holes, and then
out comes a long sticky tongue

that flicks into cracks and crevices
to lick up whatever's worth eating.

Echidnas are particularly fond
of ants and termites,

and will even climb trees
to find them.

This particular female
has an unusually healthy appetite
because she's about to breed.

And the way she does so
is the reason why the echidna
is such a truly weird mammal.

The echidna doesn't give birth
to live babies. She lays an egg.

It's hidden in her fur in a shallow
depression on her underside.

It's no bigger than a marble.

Inside it, a young echidna
is slowly developing.

After her baby hatches,
she carries it around on her
underside for about 50 days,

until it begins to develop spines.
She then deposits it in a burrow,

where it stays and grows
for nearly seven months.

But how does she feed it
during this long time?

To answer that question, we need
to find the only other egg-laying
mammal in the world today.

And it too lives here in Australia.

Just surfacing beside me here

is one of the most
extraordinary animals.

So bizarre
that, when specimens of it were
first sent from Australia to Europe,

people thought it must be a fake.

But it's not.

It's real... It's alive...

It's a platypus.

That bill looks as though
it should belong to a duck,

but it's not hard
like a bird's beak - it's rubbery.

Like the echidna, the platypus
feeds on small invertebrates,

but it looks for them underwater.

Once it's collected a mouthful,
it takes them up to the surface
and grinds them to a pulp.

It doesn't have teeth, but horny
plates inside the bill do the job.

But how does it find that food?

Underwater,
it closes its white eyelids tight,
so it can't see anything.

But it has a remote-sensing device -
its bill.

As it sweeps it from side to side
like a metal detector,

sensors in it pick up
the infinitesimal electric currents

that are given off
by ALL living things.

There were very few other mammals
on Earth 100 million years ago
when the first platypus appeared,

but there was another animal
hunting in rivers.

Birds.

As the platypus grubs around
on the riverbed, it attracts fish,
which the cormorant then snaps up.

Water birds are among
the most ancient bird families,

so this could be a scene just
after the death of the dinosaurs,

when a new kind of animal
had appeared on Earth -
one with warm blood and fur.

The platypus has had enough.

She's heading back home
for her breeding burrow.

For there, at the end of a tunnel
that may be 20 yards long,

safe in a leaf-lined
nesting chamber, she's laid an egg.

Exactly what goes on
inside her nest no-one really knew.

No-one had even succeeded
in breeding platypus in captivity
until very recently,

and, certainly, no-one at all
had ever seen inside an occupied
platypus's nest...until now.

We have bored, very carefully,
a hole into the nest that lies
below here and inserted this tube.

This is an optical probe
with a little light on the end,
and I can manipulate it like this...

..so that I can scan it.

If I then insert that inside this
tube, I'll be able to see something

that no-one has ever seen before.

Aha. That's her in close-up.

There's her eye, her ear.
It looks as though she's seen us.

Yeah, she's... She's nibbling it.

Oh, not worth eating.

She doesn't seem
particularly disturbed by it.

But has her egg hatched?

I think that quivering may
have something to do with feeding.

I'll move the camera
and see what's going on.

Yes. And there it is - its milk.

Milk is the perfect food.
It provides the growing youngster
with everything it wants,

and only mammals produce milk.
In most mammals, of course,
it comes from a nipple,

but in this very primitive mammal,
it simply oozes through the skin.

She's leaving.

Off she goes.

The end of her furry tail.

But what's that among the leaves?

And there it is.
Yes. That's her baby.

I'll zoom in on it.

Now, you can see it.
A tiny little grub-like creature.
It's naked and blind.

On its bill is a tiny spike.
That's an egg tooth that it used
to cut its way out of its shell,

in just the same way
as reptiles and birds do.

It can only be a few days old.

The platypus and echidna are the
only mammals alive that lay eggs -

living links
with the egg-laying reptiles
from which mammals are descended.

They're both so well-adapted
to their ways of life

that they're still very successful
and are widespread in Australia.

That's an achievement - for they've
been around for 100 million years,

as the fossil evidence makes clear.

Most of that evidence
is just tiny fragments,

but at Riversleigh, in Northern
Australia, it's a different story.

50 million years ago, Australia was
much wetter than it is today, and
just here was then a swampy area.

The bones of animals
that died in or around those swamps

became buried in limey mud
at the bottom of the pools
and are now preserved in limestone.

This rock is full of bone.
Here's the rectangular boney plate
from the back of a crocodile.

The rest of it
looks as though it's bird bone.

But the limestone in which these
bones are embedded is so hard,

that the only way to get them out
is to put the whole block
in a bath of acid for a few weeks.

The limestone then dissolves away,
and what is left is sometimes
the most extraordinary bones -

beautifully preserved.

This is the skull

of an extinct platypus -
about 15 million years old.

It's been called Obdurodon,
which means enduring tooth,

because unlike today's platypus,
which has no teeth,

this one still has them. They're
the empty sockets of the molars.
They're two little premolars.

But what was this place like
15 million years ago,
when Obdurodon was alive?

The night sky would have been
full of the calls of animals

in the surrounding
lush tropical forests.

Obdurodon would have spent
much of its time swimming in pools.

But in the trees there were other
mammals of a rather different kind.

Marsupials.

There were many different kinds
of possums - very similar
to those alive today.

Down on the ground, though, there
were less familiar creatures - like
this large marsupial leaf eater.

Nothing like it is alive today.

There were great numbers of small
mouse-sized animals which, judging
from their teeth, ate insects.

Others had a taste for flesh.

Preying on these small animals -

a marsupial lion...
LION GROWLS

..which was certainly big enough to
make a meal of an unwary Obdurodon.

As the millions of years passed,
Australia began to dry out.

The rainforests retreated
and were replaced by grassy plains.

And as the landscape changed,
so did the marsupial mammals.

They thrived and diversified
into many different species,

and are still abundant today.

They differ from the platypus and
echidna in the way they reproduce.

Instead of laying eggs,
they produce young

without protective shells. And this
grey kangaroo is about to do so.

Out comes not a shelled egg, but
a tiny underdeveloped little worm.

It weighs less than a lump of sugar,

it has no back legs,
but it has forelegs,

and they are just strong enough
to pull it through its mother's fur.

It's started on
an extraordinary journey.

To survive, it must get to a pouch
higher up on its mother's belly.

Instinctively, this tiny
living particle climbs upwards

against the pull of gravity
and towards the smell of the pouch.

After about three minutes,
it reaches the lip of the pouch
and clambers down to safety inside.

There, it clamps its tiny mouth
on its mother's nipple

and takes its first meal of milk.

As it grows, the ingredients of the
milk coming from the nipple change

to ensure that the infant gets
exactly the nutrients it needs

for each stage of its development.

By the time it's nine months old,
it's getting a bit cramped - it's
time to enter the outside world.

It's almost like a second birth.

He's a little unsteady at first,
but Mum offers a helping hand.

Now, he's known as a joey.

It's all a bit much for one day,
and he heads back to mother's pouch.

It will be another year
before he's fully independent.

Other marsupials
have taken to the trees - koalas.

They too have pouches.

Indeed, it's the Latin word
marsupial, meaning pouch or purse,
that gives the whole group its name.

When a koala joey emerges,

it clings tight to Mother
for several days

before it risks going solo.

Koalas feed on gum tree leaves -
eucalyptus.

But they're hardly an ideal food.
They're tough, indigestible

and full of unpleasant chemicals.

The youngster learns from Mother
how to pick the palatable leaves.

But even these contain little
nourishment, so koalas eat a lot

and spend almost all
their waking hours doing so.

And when they're not feeding, they
conserve energy - they go to sleep.

Only koalas can live on a diet
of these particular gum leaves.

Australia seems to be full of
difficult diets in awkward places,

but there are marsupials that can
deal with almost every one of them.

The vast continent of Australia
stretches from the temperate
and sometimes chilly south,

right up into the tropics.

In the centre
there are dry sun-baked deserts,

where it's only too easy to die
from thirst.

There are mountain ranges, which
in winter are crested with snow.

But the mammalian characteristics
of warm blood and insulating fur

enables marsupials
to cope with almost anything.

The wombat has fur so thick that it
can remain active throughout winter,

even in the coldest parts
of Australia.

It feeds on grass and other plants,

and the strong front limbs,
with which it digs itself burrows,

are equally good
at clearing away snow to find food.

Its pouch opens backwards,
so that the youngster doesn't get
a face full of snow, as Mum digs.

Numbats live in woodland.

But, even there,
it can get quite cold at nights,

and this family are warming
themselves in the early morning sun.

Fur needs to be kept
in prime condition,

if it's to function as an insulator,

so grooming is essential.

These dry eucalyptus forests
may look unpromising
as a source of food,

but there are plenty of termites.

Numbats have just the right
equipment to collect them.

That spectacular tongue
has to be kept well-anointed
with sticky saliva,

and numbats spend some time
making quite sure that it is.

With gear like that, a numbat can
collect 20,000 termites in a day.

This creature's ancestors
might also have used their tongues
to collect insects,

but the mammal tongue
is a highly-adaptable instrument.

and now, the honey possum uses it
to gather pollen and nectar.

It's one of the most
specialised feeders of all mammals.

Its tongue has a brush on its tip,

which soaks up nectar
from even the deepest flowers.

These boulders are home to
a less-fussy marsupial, which will
collect whatever food is around.

At the moment,
there's an unusual delicacy -

these moths sheltering
from the summer sun.

The mountain pygmy possum might be
small, but it has a huge appetite.

Moths provide a fast-food snack,
high in energy-rich fat,

and the pygmy possum will eat
as much as it can, and put on fat
to see it through leaner times.

Only the indigestible wings
are discarded.

At other times, the pygmy possum
lives on berries and seeds -

picking them off
with its nimble fingers.

The striped possum
has a particular taste for grubs.

It lives in the few fragments
of rainforest

that survive
in North-Eastern Australia.

It's got all that's necessary
to collect them -

an excellent sense of smell,
strong teeth to chew away the bark
and a long sticky tongue.

But perhaps the most challenging
of all Australian environments

is the arid hot desert
at the continent's heart.

There is little to eat, little
to drink and few places to hide...

..but marsupials
have colonised this country, too.

Everybody would recognise those
as kangaroos...

..but the kangaroos belong
to a very big family - there are
kangaroos, wallaroos and wallabies,

big ones and small ones.
These are red kangaroos -

the biggest of the family.
They're particularly at home
in this dry country.

This can be
one of the hottest places on earth,

so red kangaroos don't
have to worry about keeping warm.

Their problem is overheating.
All mammals can sweat to lose heat,

but water is in short supply here,

and red kangaroos only do so
when they are on the move.

Instead, during the hottest
part of the day, they make use
of whatever shade they can find.

Wiping saliva on their forearms

helps to lose unwanted heat.

Blood vessels are close to the
surface of the skin - and as the
saliva evaporates, the blood cools.

They only feed in the morning
and evening, when it's cooler.

When they do, it's hard
not to notice the extraordinary way
by which they get about.

The tail acts
rather like a fifth leg,

propping up the kangaroo as it
swings forwards its huge hind limbs.

It looks ungainly
when they're moving slowly,
but when a kangaroo senses danger,

the advantage of these unusual
proportions becomes very obvious.

Hopping at full speed

a kangaroo can outpace a racehorse.

They're the only large mammals
in the world that have developed
this way of getting about,

but it's a very efficient way
of doing so.

Tendons in the back legs act like
giant springs - storing energy
as the kangaroo lands

and then releasing it
to propel the animal forward.

By recycling energy like this,

kangaroos can quickly cover
vast distances to escape predators
or to search for food and water.

It's not just out on the flat
that hopping works well - some
marsupials hop around on cliffs.

The rock wallaby's key to success
lies in its feet.

The soles have thick corrugated
skin - pads which give them a grip
on every kind of surface.

The wallaby can bounce about this
difficult terrain with confidence.

There's little to drink here,

and though adults get the fluid
they need from their diet, growing
youngsters may find that difficult.

This youngster is after an extra
drink. Rock wallabies are able
to bring up fluid from the stomach

to ensure that their young don't go
thirsty. It's a special adaptation
to this arid environment.

Grey kangaroos
live out on the relatively
well-watered grassy plains.

They are among the most sociable
of all Australian marsupials,

but living in groups can lead
to problems in getting on together.

Last season's joeys
are fast approaching independence,

which means that their mothers
will soon be ready to mate again.

Males use their sense of smell
to find out
if a female is sexually available,

and will court her for several days.

Having found one
who seems to be promising,

a male stays close to her side
to try and ensure that HE,
and no other male, mates with her.

The most dominant male

is likely to be the one to father
most of the next generation,

and that is worth fighting for.

Joeys also fight,
but it's just play boxing -

a way of learning skills that
will be important in later life.

But it's not always a fair fight.

Fortunately,
this little one still has Mother
to see off the neighbourhood bully.

Marsupials first appeared
about 100 million years ago,

towards the end
of the age of the dinosaurs.

Then, Australia
was part of a great supercontinent,

but as the millions of years rolled
by, that continent began to split
apart. One fragment drifted south -

Antarctica. As it got closer
to the South Pole, so it got colder,
became covered with snow and ice

and its animal inhabitants died out.

A second part was Australia.

It drifted north and got warmer.

And here marsupials flourished.

But there was a third part.
It too drifted north.

It too had a population of
marsupials. And they're still there.

That was South America.

It may well have been in
this region of the supercontinent

that the marsupial mammals
first appeared. Many died out, but
there are STILL a lot of survivors.

This is one
of the most elusive of them.

It lives in the streams
of the Amazon forest

and operates only at night -

getting around in the blackness
by feeling its way with its front
paws and luxuriant whiskers.

It's the yapok or water opossum.

These pictures,

taken with infra-red cameras, may
well be the first time it's been
filmed in its natural environment.

It's hunting for fish
and crustaceans.

Its fur is so thick
that its skin doesn't get wet.

It has webbed feet
to propel it through the water.

It's too dark
for even the sharpest eyes

to see very much.

The yapok relies on its
acute sense of smell and hearing
to locate its food.

It swims with its arms apart,
groping for its prey
with its highly-sensitive fingers.

It usually takes its catch

to the shelter of nearby vegetation
to devour it.

But it doesn't only feed
in the shallows.

The yapok has a large territory,

and there are many deeper pools
in which to swim.

Underwater, it swims with its eyes
shut, like the platypus,

and hunts entirely by feel.

The female yapok can also
shut her pouch, and does so
with such muscular strength

that water doesn't get in and
drown her babies, though, no doubt,
they must be close to suffocation

after a few minutes of fishing.

It's been a good night's hunting,

and the yapok retreats
to its burrow as day breaks.

The yapok is the only
aquatic marsupial in the world.

Most of the marsupials in
Central and South America live high
in the canopy of the rainforest.

Just how many there are up there
no-one really suspected,

until scientists
started using cranes, like this one.

Apparatus like this gives such
easy access to this high canopy

that it's now possible
to get an accurate idea

of just how rich wildlife is
up here.

While we might think of Australia
as the land of the marsupials,
in places, this rainforest

may have more of them
than any other kind of mammal.

Most of them are strictly nocturnal.

And though they are abundant,
they, like everything else in these
forests, can be difficult to spot.

Many are similar
to this woolly opossum -

tree dwellers with few
specialisations and a broad diet,

which can include flowers, fruit
and insects.

These marsupial mammals, of course,

reproduce in just the same way
as their Australian relatives.

They give birth to babies at a very
early stage in their development.

Their pouch isn't as well formed

as that of a kangaroo or a koala,

but their young survive, clinging
to their mother's underside.

Marsupial mammals
dominate Australia,

and flourish in the forests
of Central and South America,

but, alongside them, are living
a different kind of mammal -
a kind to which we ourselves belong.

And it's only that kind that you
find everywhere else in the world.

The plains of Africa, for example,
have an abundance of mammals,

but not one of them is a marsupial.

They all reproduce
in a fundamentally different way.

This wildebeest has nourished her
baby within her

by means of a remarkable organ on
the wall of her womb - a placenta.

It's a circular pad, rich in
blood vessels, that is connected
to her baby by the umbilical chord,

through which she has fed
her growing youngster.

Blood vessels from the baby run up
through the chords of the placenta,

and pass so close
to those of its mother,

that they're able to
absorb nutrient from her blood and
carry it back to the unborn infant.

But all this is about to change.

Giving birth to
such a large highly-developed baby
places great strains on the mother.

It's pretty traumatic
for the baby, too.

There's a great advantage
in being born this way.

There are plenty of animals around
for whom a new-born calf

would make a welcome meal.

But this mammal baby, reared
with the help of a placenta,
is able to get to its feet

within minutes of its birth.

And while it's finding its balance,
its mother is there to defend it.

Now, the baby can be fed,

in the same way as all mammal
babies, with its mother's milk.

Placental babies may still have
months, even years to go,

before they are fully independent.

Those early months, when they were
protected in their mother's body,

have given these babies
an invaluable start in life.

So whether mammals lay eggs
or give birth to live young,

whether their babies
develop in a womb or in a pouch,

they've managed to live
almost everywhere.

The warm-blooded, furry,
milk-producing, mammalian body,
in all its multitudinous variations,

really is a winning design.

The duck-billed platypus
seems to me

just about the most extraordinary
animal alive in the world today.

I first tried to film it some
25 years ago for Life On Earth.

We offered a generous grant
to any scientist who could work out

how we could peek inside
the breeding burrow of a platypus.

There were no takers. Everyone
said it was quite impossible.

This time, with new technology,
we've managed to do just that.

Europeans first encountered the
extraordinary platypus in 1798.

200 years later,
we barely understand even
the simplest aspects of its life.

Piecing the evidence together
has proved
a fascinating detective story.

Helping us unravel the mystery
is platypus scientist Tanya Rankin.

When the first platypus skin
was sent to England,
scientists thought it was a hoax.

And they poked and prodded
and jabbed at this thing

thinking that it was a bill attached
to a skin, but it was a real animal.

Some scientists took it personally
that there was this mammal that
did not fit their classification.

They had this rigorous idea of what
a mammal, a reptile and a bird was,

and the platypus was a bit of each.

It took at least 100 years before
it was confirmed that they laid eggs.

Egg-layers like the platypus or
echidna, and the possums, both have
a quite extraordinary birth process.

25 years ago, when filming
Life On Earth, we may have failed
to film the platypus birth,

but we did make progress. For the
first time ever, we filmed this -

new-born opossums moving from the
birth canal to the mother's pouch.

But the birth itself happens
so quickly, and the babies are
so small, we thought we'd missed it.

Only when we looked at the film
frame by frame did we see the moment
of birth in this Australian possum.

But this is a scientific image,
not a natural one. That
was the challenge this time around.

We've been getting pictures
of what goes on in a breeding
burrow or nest hole for some time.

The standard way is to set up
a breeding colony, and then provide
them with an artificial nest hole

in which you have preformed holes
in which you can put your camera.

But that wouldn't work with
duck-billed platypus. Platypus
had never been bred in captivity.

It would have to be in the wild.
One of the first people
to do such a thing was Simon King,

who worked with another creature
that lives beside rivers
and burrows holes in the bank.

Not a mammal, but a bird -
the kingfisher.

How do the two compare?
Kingfishers are brightly-coloured
spectacular birds -

not common, but very conspicuous.
Not so, the platypus.

Platypuses are really difficult
to see in the wild. They're brown,
they come out at dusk -

very low profile in the water.
So you could be walking past one
and you wouldn't even know it.

They live in similar places.
This a typical platypus river,

while Simon found his kingfishers
in a Somerset peat cutting.

When an adult bird
flies into a hole carrying a fish,
you know she's got young inside,

but that's not possible
with a platypus. Because
a female feeds her young with milk,

you can't tell whether one
is a mother or not. Tanya needed
technology to locate a nest burrow.

I work with radio tracking -
looking at their movements

and what sort of habitat use
they have of the river.

I track them to their burrows
during the day and find out
where the nesting chambers are.

Once Tanya had located a burrow,

Mark Lamble handled the camera work.

Birds are a joy. Once they have
chicks, their bond is very strong

and they'll return to the nest.

With patience and care,
you can use large-scale methods
to look inside that nest.

The platypus would be
far more sensitive to disturbance.

This meant that it was
one turn at a time for Mark.

It took 10 hours in the sun
before they could insert the probe.

The first burrow
wasn't used as a nest.

It's painstaking work. The final
stages are similar for both teams.

Finally, Simon filmed the behaviour
he was looking for.

And after three nests,

I saw inside a burrow
for the first time

thanks to Mark and Tanya.

It was an incredible experience,

because it was something that had
never been done before - to actually
look inside a living, active burrow.

It's so hard to describe.
It was just incredible.

And, finally, I saw the image
I had waited 25 years to see.

Ah!

That little baby platypus,
that we caught on camera,

could not have been more than
3cm long - shorter than my thumb.

The colour of it just amazed me.

It never occurred to me
that you'd get a magenta platypus.
It was astounding.

I learnt a lot
about the workings inside a burrow.

Even the structure of the nest,
with the way the leaves lie,
what they're made of,

gave me a better understanding
of the ingenuity of these animals.

Although we've discovered
a great deal about the platypus
in recent years,

we still don't fully understand
the function of that
extraordinary feature, its bill.

It's rubbery, covered in skin
with a good blood supply
and a lavish network of nerves.

The platypus brain has a larger
area receiving nerves from the bill
than either its eyes or ears.

So what is the bill detecting?

An early naturalist, Harry Burrell,
always thought that platypuses had
to use some sort of a sixth sense,

because they close their eyes,
ears and nostrils underwater,

yet they can capture tiny prey,
such as insects and shrimp.

It wasn't until 1986 that scientists
ran experiments with platypuses

just using a nine-volt battery, to
see if platypuses could sense that.

They were astonished at the results.
This sensory system has
not been found in any other mammal.

It's called electroreception -

and the detectors are tiny pits
on the bill.

Magnified 1,000 times,
this is what they look like.

They're incredibly sensitive -

detecting electrical currents that
are given off by muscle activity

and that carry very well in water.

The tail flick of a shrimp
can be picked up by the platypus.

They use electroreception
for hunting prey,
but also for navigation underwater.

They do this triangulation thing
with the electrical sense

and then this delayed physical
movement of the water, and
they pick that up with these bills

and they manage to collect up
enormous amounts of food.

They can eat up to 25-30% of their
body weight every night. It's tiny
insects that they are picking up.

The platypus can read a riverbed
in a very different way to us.

Even trying to visualise how
the system works is a challenge.

It shows that, far from a joke,
the platypus is a unique animal

that's developed some very special
and very successful features

at the dawn of the life of mammals.

In the next programme of The Life
Of Mammals, we meet insect hunters.

These mammals
race to conquer the planet,

and they now include the most
bizarre mammals ever to walk
the Earth or to take to the sky.