Plant Predators The Life of Mammals

The biggest predator to walk the Earth today faces a continuous struggle.

Its prey is heavily armoured,

often indigestible, sometimes even poisonous.

What makes this struggle between predator and prey surprising

is that the predators are elephants and the prey are plants.

These herds are the task force

in a war that has been fought for millions of years

and has produced some of the most complex and highly evolved relationships in the natural world.

In this tree, there is one of the most extraordinary plant predators.

It's one animal that I don't need to sneak up on.

Boo!

This extraordinary creature is half-blind, half-deaf,

and this is just about as fast as it can move.

That's what can happen to you if you live on nothing but leaves.

It's a sloth.

It's not exactly an enthusiastic leaf-eater.

A couple of half-hearted chews and the leaves go straight down to its stomach.

Leaves, however, are not easily digested.

The sloth's technique is to give them time.

Then eventually, this mobile compost heap pulls itself together

and starts on a long and dangerous journey.

This is a very unusual sight - a sloth in a hurry.

It wants to defecate and the only place it is happy doing that - oddly enough - is down on the ground.

It only does it about once a week,

but why does it come down to the ground to do it?

And why does it nearly always choose to do so in exactly the same place?

Whatever the reason, it must be very important, for a sloth on the ground is almost helpless.

Any predator could attack it and it doesn't have the speed to escape.

Why it comes down in this way is a mystery. Nobody knows.

Now it's finished

and back it goes, up to the safety of the canopy.

Leaves are not very nutritious.

The sloth's way of compensating for that is not to eat more but to do less.

Its claws hook over the branches, so that the sloth can hang

without any effort of its muscles, which have been reduced to thin ribbons.

And to save energy, it spends most of its time hanging around,

half-asleep, in the tree-tops.

So with very little muscle, and a reaction time only a quarter as fast as ours,

how does a sloth's day compare with our day?

In the time it takes me to write a few letters, the sloth just about manages to groom itself.

While we have our lunch, the sloth nibbles a few leaves.

And then, as we film a sequence for the series, it's time for another nap.

Not surprisingly, many mammals in the world are dependent upon plants.

We live, after all, on a green planet.

Plants capture the energy they need to grow from the sun

and turn much of the Earth's surface into a vast and varied salad bowl.

But the leaves' nutriment is locked away within a mesh of cellulose walls.

No mammal, by itself, can digest cellulose

and those that eat leaves rely on bacteria in their stomachs to break through this dense lattice.

Broad-leaved trees first appeared on Earth about 100,000,000 years ago.

Gradually they spread, eventually forming lush rainforests, like this one in South America.

And it was in places like this

that the early mammals first started to eat leaves in a wholesale way.

One of those primitive plant predators, with very little change, still survives here today.

There's its track.

The prints are very fresh, so it could be quite close.

The animal I'm following is said to be as difficult to see as a jaguar.

And I must be careful because it's also said to be quite dangerous.

There it is.

This is the largest animal in the whole of the South American rainforests.

It's a tapir.

There's a female on the left and a small half-grown calf on the right.

With a calf there, she could be a bit aggressive.

I'd better not get too close.

They're feeding on leaves.

In fact, most of their meals are made on leaves.

You would think they've got more than enough to choose from,

but they are extremely selective about which leaves they choose.

And you can see why.

Many of the leaves are protected by spines.

Branches and trunks are armoured, too, and spikes like these can inflict real damage.

Even plants which appear harmless may have such defences, if you look close enough.

Their tissues are loaded with poison,

some of which are really powerful, such as strychnine.

But tapirs have found ways of dealing with THAT problem.

They eat only a little of any one kind of leaf, then move onto another,

so that they don't get a lethal dose of any particular one.

And they have another defence against poison.

This river bank is a special place that has been visited by tapirs over many generations.

It's eating earth -

kaolin, a special kind of clay, that binds to poisons,

neutralising them before they cause any harm.

The kaolin is a medicine. We ourselves use it for the same purpose when we have stomach-ache.

So, in spite of all the defences that plants have evolved,

tapirs manage to find all the food they need in these forests.

This struggle between mammals and the plants they feed on is waged all over the world.

The Canadian Rocky Mountains, and the beginning of an autumn day.

A pika, a member of a small community

that lives among the tumbled boulders bordering a mountain meadow where they all feed.

SQUEAK! SQUEAK!

That's a warning call, telling other pikas that this patch is now taken.

Pikas start their foraging early in the morning.

They eat all parts of a plant, not just leaves, but the flowers as well.

Grazing out in the open is dangerous.

There are eagles around, so the pikas never stray very far from the safety of the rocks.

There may seem to be plenty of food now,

but soon there will be the first flurries of snow, the flowers will die back and winter will be upon us.

What happens then when little is growing?

Well, watch what happens to these if I leave them just there.

It's not eating my flowers - at least, not yet.

It's stacking them in its larder,

creating a store that will last it through the hard days to come, when this valley will be covered in snow.

It will need a stack several feet thick if it's to survive the winter.

The strange thing is that many of these leaves are extremely poisonous.

So, why does the pika collect them?

Well, the poison acts as a natural preservative,

and the leaves remain fresh until midwinter, so in the end the poison works to the pika's advantage.

But the pika's preparations are more subtle than they might seem.

It collects a variety of plants.

Those with only a little poison will become edible quite quickly,

whereas those with a lot will remain fresh until almost the end of winter.

Each little pika may make several hundred trips a day, literally making hay while the sun shines.

Sometimes the problem is not what's in your food, but what is not.

Dealing with dietary deficiencies has had a dramatic outcome

here on the flanks of Mount Elgon in East Africa.

The first Europeans to visit these caves noticed marks like these in the walls

and they imagined that maybe they had been made by ancient Egyptians

who came here to mine for gold and precious stones.

These grooves do look like the marks made by a pick-axe,

but to discover what actually made them, you have to wait until nightfall.

We've set up infrared lights that the animals can't see, but our cameras can.

I will be able to keep watch from the safety of a side chamber.

The bats are preparing to leave to search for their food in the night skies outside.

In a few minutes' time, it will be as dark outside as it is in here.

Something is moving.

Bushbuck.

They're looking extremely nervous.

And that's why. There's a buffalo close by.

They're only a few feet apart, but they can't see one another.

You've got to remember that, as far as it is concerned, it's in pitch blackness.

It seems to be searching for something.

It's eating.

I can see its throat as it swallows,

and it's understandably very nervous and apprehensive.

It's licking salt.

The bushbuck has heard something.

It sounds like distant thunder.

It's an elephant.

IT TRUMPETS SOFTLY

Every foot's being placed very carefully.

THUD

Oh!

He bumped his head, Well, no-one's perfect.

This deep rumble, this resonating noise that's coming from him,

that's probably a signal to others waiting outside the cave, because he's by himself at the moment.

RUMBLING SOUND

That's the picture from our cave-mouth camera.

The rest of the herd have arrived and are climbing up to the entrance.

How they are managing this steep slope, I just don't know.

There's even a young calf among them.

Maybe the male's rumbles were messages to say that all is safe.

They are following exactly the same path that the male took.

Look how the female is using her trunk to guide her calf over the cave floor.

Has she detected one of our cameras?

Maybe not.

But they clearly know where they are going.

The passage here is so narrow, the big male can only just squeeze through.

SCRAPING

And now I can hear that noise. He's using his tusks to gouge out the salt.

And of course it's falling to the ground.

So what he does now is use his trunk to sniff it up

and then blow it into his mouth. You can hear that, too.

Elephants must have been coming here like this for centuries,

each generation deepening the cave a little

and passing onto the next its knowledge of the route through the darkness to the precious salt.

So the marks near the cave entrance were not made by ancient Egyptians but by elephants.

Could this great cavern have been created by them?

It's surely an extraordinary thing that elephants should choose to come to a cave,

go into its depths, then travel for hundreds of yards through total blackness.

It's a dramatic demonstration of how important a mineral can be to an animal.

So the demands of diet have had the extraordinary effect of turning elephants into salt miners.

Plants make themselves indigestible, defend themselves with spines and poisons and are so poor in nutriment

that their predators have to go to great lengths to get dietary supplements.

Yet despite all this, plant-eating mammals are a great success story,

and nowhere more spectacularly so than out here on the open plains of Africa.

Here plant predators gather in unparalleled numbers,

the greatest concentration of mammals to be found on Earth.

The leaves they seek are those of one particular kind of plant - grass.

The relationship between them and their prey is very complex.

Grass is not as passive as it might appear.

The edges of its leaves are armoured with tiny spines.

And inside its tissues there are needles of silica.

Grazers, in response, have developed countermeasures.

They have teeth that grow continuously up just as fast as they are worn down.

And they digest everything twice.

Each mouthful, after being chewed, goes down into a multi-chambered stomach for a first processing

and is then brought up again for further mastication.

This second chewing can be done at leisure and in relative safety,

for instead of having your head down to graze, you can now keep it up, watching out for danger.

The leaves go back for a final treatment in a different chamber of the stomach.

What nutriment is left is returned to re-fertilise the plants from which it came.

But there is a season each year when the rains stop and the grass shrivels.

The grazers have to find food elsewhere.

The annual migration has started.

Such yearly compulsions grip grazers all over the world.

In Alaska, caribou also have to move to escape the worst privations of the Arctic winter.

But wherever the migrating plant predators travel, they are beset by animal predators.

Only from the air can you get a real impression of the vast scale of these annual upheavals.

Every year, millions of animals travel hundreds of miles

across burning hot plains and freezing cold tundra.

But what is the real reason for these extraordinary, risky journeys?

Speed up the movements of the herds and a pattern appears.

The wildebeest are following special trails in the grass.

Grass may all look the same, but in fact it varies in one particular component

that we now know is essential for the survival of the wildebeest - phosphorus.

Wildebeest can tell which grass is rich in phosphorus and which is not,

so they graze some parts and ignore others.

They time their migration to arrive on the short-grass plains of the Serengeti

just as phosphorus-rich grasses are beginning to sprout.

But before long this grass will also dry out and then the herds will be forced to move again.

Although the wildebeest rob the grass of its leaves,

they don't damage the stems, so the grass continues to sprout.

A greater threat to its survival comes not from an animal, but another plant - small acacia bushes.

In due course, it may grow into a big tree.

If it does, it will compete so effectively with grass for natural resources

that grass and therefore grazers are driven away and the trees will extend their territory.

But every plant has its predator.

The dik-dik is the smallest antelope on the plains and it browses on the acacia's lowest leaves.

Its delicate pointed muzzle enables it to avoid the hooks and spines

that protect the acacia's branches from clumsier, more wholesale browsers.

The dik-dik is so small, it can't reach leaves that are more than a couple of feet above ground.

Others attack the higher branches.

The impala, with its larger muzzle and longer neck, can reach three times higher than the dik-dik.

Having taken what they need, the impala herd moves on.

But the acacia has to withstand the assault of yet another attacker.

The gerenuk is able to crop leaves that are far beyond the reach of even an impala.

Its head is very small for its height, so it can get in between the thorny branches.

And its lips and tongue are particularly mobile.

Standing erect demands special adaptations.

The gerenuk's hip joints swivel so far

that its backbone can swing up and continue the line of its hind legs.

A feeding group may have all the grace of a corps de ballet standing on their points.

But even gerenuks have to step aside when the world's tallest plant predator appears.

The giraffe.

They travel in groups of up to 30

and launch their attacks from necks that are seven-feet long.

The acacia's defences on its upper branches would deter most browsers.

But the giraffe's weaponry is formidable indeed.

Its tongue is 18 inches long and so muscular that it has a grasp.

Its neck joint is so mobile that its head can tip vertically upwards.

And its lips are so leathery, they are impervious to thorns.

The acacia is under attack from bottom to top.

With such a diversity of predators, you might think that the march of the acacia would be held in check.

But the acacia has other plans, and they're revealed during the dry season.

Throughout the year, the acacia has tantalised animals

with the chance of eating some but not all of its leaves.

Now that the time has come to shed its seeds,

that has ensured that there's a wide range of animals around to pick them up and disperse them.

Impala and other browsers crunch the pods,

but the seeds are indigestible and they will emerge unharmed with the eater's droppings.

Dik-dik might take them just a few hundred yards, impala - for a mile or so.

Giraffe can transport seeds for ten miles or even more.

But there is one predator against which the acacia has no defence.

Even the stoutest, sharpest spines don't deter an elephant

and it has a simple but devastating way of getting the branches that even a giraffe can't reach.

Its reward is a relatively spine-free meal,

for the acacia neglects to grow spines on its topmost branches

since they are beyond the reach of most browsers.

Elephants have a range of power tools with which to collect their meals.

Tusk and trunk together can cut up anything their owner fancies.

The woodier a branch, the more difficult it is to digest,

but elephants have such vast stomachs that they can allow their meals to stew for about three days.

The need for a big stomach may be one of the reasons why elephants have grown so large.

But being jumbo-sized brings other advantages as well.

Wherever there are plant-eaters, there are meat-eaters.

But even the biggest of them is not big enough to tackle an elephant.

Smaller plant-eaters are more vulnerable.

How can they defend themselves?

One way is to gather together in large numbers.

And that's what grazers do, all over the world.

If you live in a herd, there are many others around to help you in detecting danger.

Ears can be rotated to detect sound from all directions.

Sensitive noses can pick up the first faint whiff of an enemy.

Eyes with elongated pupils can keep watch across the whole horizon.

And when heads go down,

eyes swivel in their sockets to ensure that the pupil stays horizontal.

So, even when you are grazing, you can still keep an eye on what is watching YOU.

With eyes on the side of your head,

you can see both in front and behind at the same time.

This really is wrap-around vision.

Hunters' eyes point directly ahead, giving them the ability to assess range.

The targets, on the other hand, have to hold their heads sideways if they are to keep an eye on the hunter.

Sometimes the prey appears to be stalking the predator.

Grazers even taunt a hunter to make quite sure that there is no way it can launch a surprise attack.

And at this point, many hunters would give up...

but not always!

An attack is now imminent.

Sound the alarm!

VARIOUS ANIMAL CRIES

Now the time has come to run.

Herbivores have powerfully muscled hind legs that give them superlative acceleration,

invaluable if you are caught unawares.

Once again, numbers bring safety.

The North American pronghorn is the second fastest sprinter on the planet,

but over long distances it's the world champion.

But all large herbivores have to be able to run fast.

They run on tip-toe, so that they cover more ground with each stride.

Muscles are bunched at the top of the legs, so that the limbs are streamlined.

Some grazers flaunt their athleticism,

as if to say, "I'm fit, so save your energy and pick on someone weaker."

Cheetahs may be the fastest sprinters, but gazelles are better at dodging and jinking.

Slimline legs, however, trip only too easily.

And having eyes on the side of your head, so that you can't see directly forward, can be catastrophic.

Even so, herbivores manage to outmanoeuvre their enemies more often than you might suppose.

Kicking hooves and thrusting horns are formidable weapons.

This mother is going to defend her fawn, come what may.

A buffalo has incautiously strayed away from its herd.

It surely can have no defence against a group of lions.

But the rest of the herd have noticed.

Faced with the threat of hundreds of tons of massed anger, the lioness turns tail.

The male lion, however, seems unwilling to give up.

The buffalo, with their heavy armament, have won this particular battle.

But the war on the plains is a never-ending one.

You might think that these weapons are just a defence against carnivores, but not so.

Their primary use is to fight one another.

And that's the drawback of living in herds.

The Badlands of North America.

Bull bison are preparing for the annual rut.

There are only a few females on heat at any one time,

so each male tries to sniff them out before rivals approach.

The males walk in parallel, assessing one another.

Pumped up with testosterone, they paw the ground to show off their strength.

They spray the earth with their urine and then roll in it, so that they reek of their own hormones.

This combination of rolling and roaring is a clear sign that there will be a fight.

Most contests are resolved in seconds.

A few, however, escalate into full-scale battle.

The attack is usually head-on. At full gallop, the impact is titanic.

One ton moving at 30mph meeting another coming in the opposite direction.

This male is lucky to escape a fatal stabbing.

The largest horns in proportion to body size are carried by American bighorn sheep.

When armaments reach this size,

their indiscriminate deployment could be catastrophic.

Smaller males can be warned off with a simple kick.

But closely-matched males will have to fight.

The rules are strict. Contestants must meet head-on.

If contact is unbalanced, both fighters could break their necks.

An impact like that would crush a human skull like an eggshell.

So, how does the bighorn survive?

Well, its skull is heavily reinforced internally with bone,

but it also has a number of hairline cracks in it

and these flex, so acting like shock absorbers.

The bighorn's weapon is a battering ram, but there are also swords, scimitars and daggers.

All are ridged and pointed at the tips and both those characteristics have important functions.

Before any physical contact is made, the males, no matter what their species, size one another up.

If neither retreats, horns will clash.

The V-shaped gap between the horns is always narrower than the width of a single horn,

so that it is not possible for a fighter to strike his opponent directly on the skull.

Having made contact,

the contestants wrestle and now the function of the ridges becomes clear.

They prevent the horns from slipping and enable the contestants to test each other's strength.

Now if there is a chance, the pointed tips will be used to stab a rival in the flank or belly.

A competitor will not waste his energy in starting a fight if he is obviously outgunned,

so horns are continually flaunted.

These male topi are even putting on war paint.

By plastering their horns with mud,

they make themselves more intimidating to other males, and more attractive to females.

Each in this gathering of several hundred must establish a small patch of territory for himself.

At first, the females wander through the pasture, perhaps sizing up the males.

And the males are torn between pursuing particular females

and battling with one another to establish their individual stamping grounds.

Again and again, a male has to fight.

Eventually each male has his own patch.

The females decide which they like best and present him with his reward.

The mating rituals go on for many days.

Males dare not leave their territory in case rivals claim it

and they have to fight repeatedly to maintain their ownership.

As the days pass, they become more exhausted and eventually they can barely stand.

They are so tired that their normal defences are down.

The most powerful males have claimed territories in the centre of the breeding ground.

The less strong have to accept those on the fringes.

And that is not a good place to be.

In spite of the circling hyenas, the males won't leave their territories.

If they did, they would have no chance of mating.

But they no longer have the will or the strength to confront the hyenas, unless they are attacked.

For most of the year, when the topi grazed in the herd, they kept watch for one another,

but the competition to breed has changed all that.

The dangers of eating grass out on the open plain led the topi to live in herds.

Now the price of doing so is being paid...

by the weaker males.

From the topi's battle to breed to the great migrations of the world,

the underground mines of Mount Elgon

and the extraordinary shape and size of the wonderful creatures that made them,

all these stem from the apparently simple act of eating leaves.

So, as always in the Life of Mammals,

what you eat determines what you are.

Elephants are surely the most impressive, the most formidable of all plant predators.

They are, after all, the biggest of all land animals.

And yet they can suddenly appear or disappear absolutely silently in the bush.

They're so powerful, they can flatten your Land Rover, if they have a mind to do so.

And they're so intelligent, they have such long memories,

and they communicate within their families in ways which we are only beginning to understand.

Sitting in a canoe, watching elephants coming down to the river to drink is a marvellous experience.

But to be in a cave in the pitch blackness where you can't see them,

and yet you can hear the creak of their bodies, and that low, rumbling call, that is something else.

And to tell you about that,

here is Justine Evans,

who has spent night after night in that cave in Mount Elgon with her cameras.

It was not so much scary... I don't know even if it was dangerous,

but it felt intimidating

and quite overwhelming. It sounded worse than it was because of the cave walls.

They made the sound of the elephants resonate, so I felt that they were roaring right next to me.

There's...one, two, three, four, five...at least five in here at once, which is amazing.

They came all the way to the back and I got all sorts of shots.

The baby was standing in the dark, obviously really bored because it doesn't know how to tusk yet.

He was just doing this with his trunk and going round in circles!

The cave elephant families follow ancient traditional pathways used by many previous generations.

There's some kind of inherited culture.

Young calves, following in their mother's footsteps, may be too young to dig for salt,

but they're here to learn the traditions of Mount Elgon's elephants.

The notion that elephants might have traditions would have been unthinkable only a few decades ago.

But since then, scientists have started to study elephants by living alongside them in the field

and recognising each individual one.

No-one knows them better than Cynthia Moss who's lived in Amboseli for the past 30 years

and recognises every member of 50 families, the most famous of whom, perhaps, is Echo.

We first filmed Echo in 1993.

Since then, we've followed her reign as head of the herd.

Echo is now a grand old matriarch.

Her crossed tusks make her unmistakable.

This is her latest grandson.

Ella, with ragged ears, is her second in command.

Initially, ears identified individuals.

Their ears are never absolutely smooth along the edge.

There's usually little nicks or holes or whatever.

But after a while, you recognise the whole elephant.

Wildlife cameraman Martyn Colbeck has worked alongside Cynthia.

Together, they gained a deeper insight.

Cynthia Moss's knowledge of individual elephants

has been very significant for us.

It would have been difficult for me to do it on my own

as I did not know the individuals and how they related to each other.

Cynthia and Martyn were accepted as part of the family.

I think one of the most exciting things I've ever seen and filmed with the elephants

was the birth of a calf, the matriarch's calf, in fact.

I just never thought that we'd ever be able to film it.

For the matriarch to trust us enough to give birth right next to us in the middle of the night

was quite a privilege.

And it took us several years to get ourselves into this situation.

When the delivery finally happened, the whole family went crazy.

They made sounds that I'd never heard elephants make before.

They all crowded around Echo

and it was extraordinary.

It was a magical moment.

When there's such a bond of mutual trust and understanding,

the detail of the elephants' behaviour emerges

and the drama of their lives is revealed.

Usually, Cynthia Moss was there interpreting behaviour.

There's a very good example of that when one of our family's calves was kidnapped by another family.

That's a very rare bit of behaviour and I would have had no idea that that was about to happen.

Echo gets a vicious poke in the backside when she tries to rescue Ebony from this larger family.

The other matriarch, called Vee, is using Ebony

to emphasise her dominance.

But help is on the way.

Reacting to Ebony's distress calls and Echo's alarms, the rest of the family arrive in tight formation

and plunge into the kidnappers.

FRANTIC TRUMPETING

Ebony was rescued by her family.

For some elephants, the strength of the family is even more important

and inherited traditions are the difference between life and death.

This is most clearly the case for the elephants of Namibia.

They live in desert and so they're having to move over enormous distances to find food and water.

The matriarch is like a repository of knowledge for the whole family.

They know exactly where they need to go in order to be able to feed.

They must have complex mental maps of an enormous area

because the water holes are extremely isolated and they're only there at certain times of year.

So their intelligence and mental mapping ability must be phenomenal.

And that knowledge is passed down through generation after generation.

So, now we know that tradition is an essential for the survival of the elephants.

But long migratory journeys are part of the annual cycle of many plant predators.

And it's group memory that enables some of them to make the longest journey of any land animal.

This is perhaps the most impressive migration of all.

Huge herds of caribou on their annual movements across Alaska and Canada.

And using the same principle of identifying and studying known individuals,

we can understand and film an animal tradition on a vast scale.

Very little is known about them,

although there's millions of them in Northern America and Canada.

There's a scientist working with one herd of about 900,000 animals.

25 of them are satellite collared, so that you can locate an animal in the most difficult situation.

Once a week, he got a read-out of where those 25 animals were.

From that, we'd look at this map about an area the size of France

and we'd be able to tell exactly where the animals were, so we could fly ahead and land

and film them migrating them through an area.

Technology's opening up a whole new field of behaviour that we can film.

One caribou tracked by satellite moved over 3,000 miles in one year,

the record for any land mammal.

Like some migratory birds,

caribou may have a built-in compass to help them cross unfamiliar land on the way to their calving grounds.

But, as with the elephants, herd traditions shape the movement.

What they gain from living in the herd seems to be a key factor in their survival.

In our next programme, we meet the most numerous mammals of all,

the rodents.

They use their chisel-like teeth in the most extraordinary ways and manage to live almost everywhere.

Subtitles by Dorothy Moore BBC Broadcast 2002

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