0:00:39 > 0:00:46The biggest predator to walk the Earth today faces a continuous struggle.
0:00:46 > 0:00:48Its prey is heavily armoured,
0:00:48 > 0:00:51often indigestible, sometimes even poisonous.
0:00:51 > 0:00:56What makes this struggle between predator and prey surprising
0:00:56 > 0:01:01is that the predators are elephants and the prey are plants.
0:01:01 > 0:01:04These herds are the task force
0:01:04 > 0:01:08in a war that has been fought for millions of years
0:01:08 > 0:01:14and has produced some of the most complex and highly evolved relationships in the natural world.
0:01:32 > 0:01:37In this tree, there is one of the most extraordinary plant predators.
0:01:40 > 0:01:44It's one animal that I don't need to sneak up on.
0:01:45 > 0:01:47Boo!
0:01:49 > 0:01:54This extraordinary creature is half-blind, half-deaf,
0:01:54 > 0:01:58and this is just about as fast as it can move.
0:01:58 > 0:02:04That's what can happen to you if you live on nothing but leaves.
0:02:04 > 0:02:07It's a sloth.
0:02:07 > 0:02:10It's not exactly an enthusiastic leaf-eater.
0:02:10 > 0:02:17A couple of half-hearted chews and the leaves go straight down to its stomach.
0:02:17 > 0:02:20Leaves, however, are not easily digested.
0:02:20 > 0:02:24The sloth's technique is to give them time.
0:02:27 > 0:02:32Then eventually, this mobile compost heap pulls itself together
0:02:32 > 0:02:36and starts on a long and dangerous journey.
0:02:37 > 0:02:42This is a very unusual sight - a sloth in a hurry.
0:02:42 > 0:02:49It wants to defecate and the only place it is happy doing that - oddly enough - is down on the ground.
0:02:51 > 0:02:53It only does it about once a week,
0:02:53 > 0:02:57but why does it come down to the ground to do it?
0:02:57 > 0:03:02And why does it nearly always choose to do so in exactly the same place?
0:03:02 > 0:03:09Whatever the reason, it must be very important, for a sloth on the ground is almost helpless.
0:03:10 > 0:03:15Any predator could attack it and it doesn't have the speed to escape.
0:03:15 > 0:03:20Why it comes down in this way is a mystery. Nobody knows.
0:03:20 > 0:03:22Now it's finished
0:03:22 > 0:03:27and back it goes, up to the safety of the canopy.
0:03:27 > 0:03:29Leaves are not very nutritious.
0:03:29 > 0:03:35The sloth's way of compensating for that is not to eat more but to do less.
0:03:35 > 0:03:38Its claws hook over the branches, so that the sloth can hang
0:03:38 > 0:03:42without any effort of its muscles, which have been reduced to thin ribbons.
0:03:42 > 0:03:48And to save energy, it spends most of its time hanging around,
0:03:48 > 0:03:50half-asleep, in the tree-tops.
0:03:51 > 0:03:57So with very little muscle, and a reaction time only a quarter as fast as ours,
0:03:57 > 0:04:01how does a sloth's day compare with our day?
0:04:01 > 0:04:08In the time it takes me to write a few letters, the sloth just about manages to groom itself.
0:04:08 > 0:04:13While we have our lunch, the sloth nibbles a few leaves.
0:04:14 > 0:04:20And then, as we film a sequence for the series, it's time for another nap.
0:04:22 > 0:04:27Not surprisingly, many mammals in the world are dependent upon plants.
0:04:27 > 0:04:31We live, after all, on a green planet.
0:04:31 > 0:04:36Plants capture the energy they need to grow from the sun
0:04:36 > 0:04:40and turn much of the Earth's surface into a vast and varied salad bowl.
0:04:45 > 0:04:51But the leaves' nutriment is locked away within a mesh of cellulose walls.
0:04:51 > 0:04:54No mammal, by itself, can digest cellulose
0:04:54 > 0:05:02and those that eat leaves rely on bacteria in their stomachs to break through this dense lattice.
0:05:03 > 0:05:08Broad-leaved trees first appeared on Earth about 100,000,000 years ago.
0:05:08 > 0:05:15Gradually they spread, eventually forming lush rainforests, like this one in South America.
0:05:17 > 0:05:20And it was in places like this
0:05:20 > 0:05:25that the early mammals first started to eat leaves in a wholesale way.
0:05:25 > 0:05:31One of those primitive plant predators, with very little change, still survives here today.
0:05:31 > 0:05:34There's its track.
0:05:34 > 0:05:38The prints are very fresh, so it could be quite close.
0:05:41 > 0:05:46The animal I'm following is said to be as difficult to see as a jaguar.
0:05:48 > 0:05:52And I must be careful because it's also said to be quite dangerous.
0:05:55 > 0:05:57There it is.
0:06:09 > 0:06:15This is the largest animal in the whole of the South American rainforests.
0:06:15 > 0:06:18It's a tapir.
0:06:19 > 0:06:24There's a female on the left and a small half-grown calf on the right.
0:06:24 > 0:06:28With a calf there, she could be a bit aggressive.
0:06:28 > 0:06:32I'd better not get too close.
0:06:34 > 0:06:36They're feeding on leaves.
0:06:36 > 0:06:41In fact, most of their meals are made on leaves.
0:06:41 > 0:06:46You would think they've got more than enough to choose from,
0:06:46 > 0:06:51but they are extremely selective about which leaves they choose.
0:06:57 > 0:07:00And you can see why.
0:07:00 > 0:07:04Many of the leaves are protected by spines.
0:07:04 > 0:07:10Branches and trunks are armoured, too, and spikes like these can inflict real damage.
0:07:15 > 0:07:21Even plants which appear harmless may have such defences, if you look close enough.
0:07:24 > 0:07:27Their tissues are loaded with poison,
0:07:27 > 0:07:31some of which are really powerful, such as strychnine.
0:07:31 > 0:07:36But tapirs have found ways of dealing with THAT problem.
0:07:36 > 0:07:41They eat only a little of any one kind of leaf, then move onto another,
0:07:41 > 0:07:45so that they don't get a lethal dose of any particular one.
0:07:45 > 0:07:49And they have another defence against poison.
0:07:49 > 0:07:55This river bank is a special place that has been visited by tapirs over many generations.
0:08:01 > 0:08:03It's eating earth -
0:08:03 > 0:08:07kaolin, a special kind of clay, that binds to poisons,
0:08:07 > 0:08:11neutralising them before they cause any harm.
0:08:11 > 0:08:18The kaolin is a medicine. We ourselves use it for the same purpose when we have stomach-ache.
0:08:18 > 0:08:23So, in spite of all the defences that plants have evolved,
0:08:23 > 0:08:27tapirs manage to find all the food they need in these forests.
0:08:31 > 0:08:38This struggle between mammals and the plants they feed on is waged all over the world.
0:08:41 > 0:08:46The Canadian Rocky Mountains, and the beginning of an autumn day.
0:08:58 > 0:09:02A pika, a member of a small community
0:09:02 > 0:09:09that lives among the tumbled boulders bordering a mountain meadow where they all feed.
0:09:10 > 0:09:13SQUEAK! SQUEAK!
0:09:17 > 0:09:22That's a warning call, telling other pikas that this patch is now taken.
0:09:25 > 0:09:28Pikas start their foraging early in the morning.
0:09:28 > 0:09:33They eat all parts of a plant, not just leaves, but the flowers as well.
0:09:33 > 0:09:36Grazing out in the open is dangerous.
0:09:36 > 0:09:43There are eagles around, so the pikas never stray very far from the safety of the rocks.
0:09:43 > 0:09:46There may seem to be plenty of food now,
0:09:46 > 0:09:53but soon there will be the first flurries of snow, the flowers will die back and winter will be upon us.
0:09:53 > 0:09:56What happens then when little is growing?
0:09:56 > 0:10:01Well, watch what happens to these if I leave them just there.
0:10:13 > 0:10:17It's not eating my flowers - at least, not yet.
0:10:17 > 0:10:20It's stacking them in its larder,
0:10:20 > 0:10:27creating a store that will last it through the hard days to come, when this valley will be covered in snow.
0:10:31 > 0:10:36It will need a stack several feet thick if it's to survive the winter.
0:10:41 > 0:10:46The strange thing is that many of these leaves are extremely poisonous.
0:10:46 > 0:10:48So, why does the pika collect them?
0:10:48 > 0:10:52Well, the poison acts as a natural preservative,
0:10:52 > 0:10:59and the leaves remain fresh until midwinter, so in the end the poison works to the pika's advantage.
0:10:59 > 0:11:05But the pika's preparations are more subtle than they might seem.
0:11:05 > 0:11:07It collects a variety of plants.
0:11:07 > 0:11:12Those with only a little poison will become edible quite quickly,
0:11:12 > 0:11:17whereas those with a lot will remain fresh until almost the end of winter.
0:11:17 > 0:11:23Each little pika may make several hundred trips a day, literally making hay while the sun shines.
0:12:07 > 0:12:13Sometimes the problem is not what's in your food, but what is not.
0:12:13 > 0:12:18Dealing with dietary deficiencies has had a dramatic outcome
0:12:18 > 0:12:22here on the flanks of Mount Elgon in East Africa.
0:12:33 > 0:12:40The first Europeans to visit these caves noticed marks like these in the walls
0:12:40 > 0:12:45and they imagined that maybe they had been made by ancient Egyptians
0:12:45 > 0:12:49who came here to mine for gold and precious stones.
0:12:49 > 0:12:53These grooves do look like the marks made by a pick-axe,
0:12:53 > 0:12:59but to discover what actually made them, you have to wait until nightfall.
0:12:59 > 0:13:05We've set up infrared lights that the animals can't see, but our cameras can.
0:13:05 > 0:13:09I will be able to keep watch from the safety of a side chamber.
0:13:12 > 0:13:18The bats are preparing to leave to search for their food in the night skies outside.
0:13:20 > 0:13:25In a few minutes' time, it will be as dark outside as it is in here.
0:13:28 > 0:13:31Something is moving.
0:13:31 > 0:13:33Bushbuck.
0:13:34 > 0:13:37They're looking extremely nervous.
0:13:37 > 0:13:41And that's why. There's a buffalo close by.
0:13:41 > 0:13:46They're only a few feet apart, but they can't see one another.
0:13:55 > 0:14:02You've got to remember that, as far as it is concerned, it's in pitch blackness.
0:14:03 > 0:14:07It seems to be searching for something.
0:14:10 > 0:14:12It's eating.
0:14:12 > 0:14:15I can see its throat as it swallows,
0:14:15 > 0:14:19and it's understandably very nervous and apprehensive.
0:14:21 > 0:14:24It's licking salt.
0:14:27 > 0:14:29The bushbuck has heard something.
0:14:31 > 0:14:34It sounds like distant thunder.
0:14:39 > 0:14:41It's an elephant.
0:14:44 > 0:14:47IT TRUMPETS SOFTLY
0:14:52 > 0:14:55Every foot's being placed very carefully.
0:15:01 > 0:15:03THUD
0:15:03 > 0:15:04Oh!
0:15:04 > 0:15:07He bumped his head, Well, no-one's perfect.
0:15:17 > 0:15:22This deep rumble, this resonating noise that's coming from him,
0:15:22 > 0:15:30that's probably a signal to others waiting outside the cave, because he's by himself at the moment.
0:15:30 > 0:15:32RUMBLING SOUND
0:15:35 > 0:15:39That's the picture from our cave-mouth camera.
0:15:39 > 0:15:44The rest of the herd have arrived and are climbing up to the entrance.
0:15:44 > 0:15:48How they are managing this steep slope, I just don't know.
0:15:48 > 0:15:51There's even a young calf among them.
0:16:00 > 0:16:05Maybe the male's rumbles were messages to say that all is safe.
0:16:09 > 0:16:14They are following exactly the same path that the male took.
0:16:14 > 0:16:21Look how the female is using her trunk to guide her calf over the cave floor.
0:16:28 > 0:16:31Has she detected one of our cameras?
0:16:34 > 0:16:36Maybe not.
0:16:36 > 0:16:40But they clearly know where they are going.
0:16:45 > 0:16:51The passage here is so narrow, the big male can only just squeeze through.
0:16:56 > 0:16:58SCRAPING
0:17:01 > 0:17:07And now I can hear that noise. He's using his tusks to gouge out the salt.
0:17:07 > 0:17:11And of course it's falling to the ground.
0:17:12 > 0:17:16So what he does now is use his trunk to sniff it up
0:17:16 > 0:17:20and then blow it into his mouth. You can hear that, too.
0:17:31 > 0:17:36Elephants must have been coming here like this for centuries,
0:17:36 > 0:17:40each generation deepening the cave a little
0:17:40 > 0:17:46and passing onto the next its knowledge of the route through the darkness to the precious salt.
0:17:49 > 0:17:56So the marks near the cave entrance were not made by ancient Egyptians but by elephants.
0:18:10 > 0:18:14Could this great cavern have been created by them?
0:18:18 > 0:18:22It's surely an extraordinary thing that elephants should choose to come to a cave,
0:18:22 > 0:18:28go into its depths, then travel for hundreds of yards through total blackness.
0:18:28 > 0:18:35It's a dramatic demonstration of how important a mineral can be to an animal.
0:18:37 > 0:18:44So the demands of diet have had the extraordinary effect of turning elephants into salt miners.
0:18:46 > 0:18:53Plants make themselves indigestible, defend themselves with spines and poisons and are so poor in nutriment
0:18:53 > 0:18:59that their predators have to go to great lengths to get dietary supplements.
0:18:59 > 0:19:05Yet despite all this, plant-eating mammals are a great success story,
0:19:05 > 0:19:12and nowhere more spectacularly so than out here on the open plains of Africa.
0:19:15 > 0:19:20Here plant predators gather in unparalleled numbers,
0:19:20 > 0:19:24the greatest concentration of mammals to be found on Earth.
0:19:24 > 0:19:29The leaves they seek are those of one particular kind of plant - grass.
0:19:31 > 0:19:36The relationship between them and their prey is very complex.
0:19:36 > 0:19:40Grass is not as passive as it might appear.
0:19:45 > 0:19:50The edges of its leaves are armoured with tiny spines.
0:19:52 > 0:19:57And inside its tissues there are needles of silica.
0:20:05 > 0:20:10Grazers, in response, have developed countermeasures.
0:20:10 > 0:20:16They have teeth that grow continuously up just as fast as they are worn down.
0:20:17 > 0:20:19And they digest everything twice.
0:20:19 > 0:20:26Each mouthful, after being chewed, goes down into a multi-chambered stomach for a first processing
0:20:26 > 0:20:30and is then brought up again for further mastication.
0:20:30 > 0:20:34This second chewing can be done at leisure and in relative safety,
0:20:34 > 0:20:41for instead of having your head down to graze, you can now keep it up, watching out for danger.
0:20:43 > 0:20:49The leaves go back for a final treatment in a different chamber of the stomach.
0:20:49 > 0:20:56What nutriment is left is returned to re-fertilise the plants from which it came.
0:20:56 > 0:21:02But there is a season each year when the rains stop and the grass shrivels.
0:21:02 > 0:21:06The grazers have to find food elsewhere.
0:21:13 > 0:21:16The annual migration has started.
0:21:30 > 0:21:34Such yearly compulsions grip grazers all over the world.
0:21:34 > 0:21:41In Alaska, caribou also have to move to escape the worst privations of the Arctic winter.
0:21:48 > 0:21:55But wherever the migrating plant predators travel, they are beset by animal predators.
0:22:13 > 0:22:20Only from the air can you get a real impression of the vast scale of these annual upheavals.
0:22:21 > 0:22:26Every year, millions of animals travel hundreds of miles
0:22:26 > 0:22:30across burning hot plains and freezing cold tundra.
0:22:30 > 0:22:34But what is the real reason for these extraordinary, risky journeys?
0:22:34 > 0:22:39Speed up the movements of the herds and a pattern appears.
0:22:42 > 0:22:47The wildebeest are following special trails in the grass.
0:22:54 > 0:23:01Grass may all look the same, but in fact it varies in one particular component
0:23:01 > 0:23:07that we now know is essential for the survival of the wildebeest - phosphorus.
0:23:10 > 0:23:15Wildebeest can tell which grass is rich in phosphorus and which is not,
0:23:15 > 0:23:19so they graze some parts and ignore others.
0:23:19 > 0:23:26They time their migration to arrive on the short-grass plains of the Serengeti
0:23:26 > 0:23:30just as phosphorus-rich grasses are beginning to sprout.
0:23:31 > 0:23:39But before long this grass will also dry out and then the herds will be forced to move again.
0:23:41 > 0:23:46Although the wildebeest rob the grass of its leaves,
0:23:46 > 0:23:50they don't damage the stems, so the grass continues to sprout.
0:23:50 > 0:23:58A greater threat to its survival comes not from an animal, but another plant - small acacia bushes.
0:23:58 > 0:24:02In due course, it may grow into a big tree.
0:24:02 > 0:24:08If it does, it will compete so effectively with grass for natural resources
0:24:08 > 0:24:14that grass and therefore grazers are driven away and the trees will extend their territory.
0:24:17 > 0:24:20But every plant has its predator.
0:24:20 > 0:24:27The dik-dik is the smallest antelope on the plains and it browses on the acacia's lowest leaves.
0:24:30 > 0:24:34Its delicate pointed muzzle enables it to avoid the hooks and spines
0:24:34 > 0:24:40that protect the acacia's branches from clumsier, more wholesale browsers.
0:24:40 > 0:24:47The dik-dik is so small, it can't reach leaves that are more than a couple of feet above ground.
0:25:00 > 0:25:03Others attack the higher branches.
0:25:04 > 0:25:12The impala, with its larger muzzle and longer neck, can reach three times higher than the dik-dik.
0:25:18 > 0:25:23Having taken what they need, the impala herd moves on.
0:25:31 > 0:25:37But the acacia has to withstand the assault of yet another attacker.
0:25:42 > 0:25:48The gerenuk is able to crop leaves that are far beyond the reach of even an impala.
0:25:57 > 0:26:04Its head is very small for its height, so it can get in between the thorny branches.
0:26:04 > 0:26:08And its lips and tongue are particularly mobile.
0:26:09 > 0:26:13Standing erect demands special adaptations.
0:26:13 > 0:26:17The gerenuk's hip joints swivel so far
0:26:17 > 0:26:22that its backbone can swing up and continue the line of its hind legs.
0:26:22 > 0:26:29A feeding group may have all the grace of a corps de ballet standing on their points.
0:26:56 > 0:27:03But even gerenuks have to step aside when the world's tallest plant predator appears.
0:27:09 > 0:27:11The giraffe.
0:27:12 > 0:27:15They travel in groups of up to 30
0:27:15 > 0:27:19and launch their attacks from necks that are seven-feet long.
0:27:23 > 0:27:28The acacia's defences on its upper branches would deter most browsers.
0:27:30 > 0:27:34But the giraffe's weaponry is formidable indeed.
0:27:35 > 0:27:41Its tongue is 18 inches long and so muscular that it has a grasp.
0:27:41 > 0:27:46Its neck joint is so mobile that its head can tip vertically upwards.
0:27:46 > 0:27:51And its lips are so leathery, they are impervious to thorns.
0:27:51 > 0:27:55The acacia is under attack from bottom to top.
0:27:57 > 0:28:04With such a diversity of predators, you might think that the march of the acacia would be held in check.
0:28:04 > 0:28:11But the acacia has other plans, and they're revealed during the dry season.
0:28:20 > 0:28:24Throughout the year, the acacia has tantalised animals
0:28:24 > 0:28:28with the chance of eating some but not all of its leaves.
0:28:28 > 0:28:32Now that the time has come to shed its seeds,
0:28:32 > 0:28:38that has ensured that there's a wide range of animals around to pick them up and disperse them.
0:28:38 > 0:28:42Impala and other browsers crunch the pods,
0:28:42 > 0:28:48but the seeds are indigestible and they will emerge unharmed with the eater's droppings.
0:28:48 > 0:28:55Dik-dik might take them just a few hundred yards, impala - for a mile or so.
0:28:56 > 0:29:01Giraffe can transport seeds for ten miles or even more.
0:29:04 > 0:29:09But there is one predator against which the acacia has no defence.
0:29:14 > 0:29:19Even the stoutest, sharpest spines don't deter an elephant
0:29:19 > 0:29:26and it has a simple but devastating way of getting the branches that even a giraffe can't reach.
0:29:43 > 0:29:47Its reward is a relatively spine-free meal,
0:29:47 > 0:29:52for the acacia neglects to grow spines on its topmost branches
0:29:52 > 0:29:56since they are beyond the reach of most browsers.
0:29:56 > 0:30:03Elephants have a range of power tools with which to collect their meals.
0:30:03 > 0:30:08Tusk and trunk together can cut up anything their owner fancies.
0:30:11 > 0:30:15The woodier a branch, the more difficult it is to digest,
0:30:15 > 0:30:22but elephants have such vast stomachs that they can allow their meals to stew for about three days.
0:30:24 > 0:30:30The need for a big stomach may be one of the reasons why elephants have grown so large.
0:30:30 > 0:30:35But being jumbo-sized brings other advantages as well.
0:30:36 > 0:30:41Wherever there are plant-eaters, there are meat-eaters.
0:30:43 > 0:30:48But even the biggest of them is not big enough to tackle an elephant.
0:30:48 > 0:30:52Smaller plant-eaters are more vulnerable.
0:30:52 > 0:30:55How can they defend themselves?
0:30:55 > 0:31:00One way is to gather together in large numbers.
0:31:00 > 0:31:03And that's what grazers do, all over the world.
0:31:03 > 0:31:10If you live in a herd, there are many others around to help you in detecting danger.
0:31:17 > 0:31:22Ears can be rotated to detect sound from all directions.
0:31:30 > 0:31:35Sensitive noses can pick up the first faint whiff of an enemy.
0:31:41 > 0:31:46Eyes with elongated pupils can keep watch across the whole horizon.
0:31:48 > 0:31:50And when heads go down,
0:31:50 > 0:31:57eyes swivel in their sockets to ensure that the pupil stays horizontal.
0:31:57 > 0:32:03So, even when you are grazing, you can still keep an eye on what is watching YOU.
0:32:06 > 0:32:09With eyes on the side of your head,
0:32:09 > 0:32:13you can see both in front and behind at the same time.
0:32:14 > 0:32:18This really is wrap-around vision.
0:32:29 > 0:32:35Hunters' eyes point directly ahead, giving them the ability to assess range.
0:32:37 > 0:32:44The targets, on the other hand, have to hold their heads sideways if they are to keep an eye on the hunter.
0:32:47 > 0:32:51Sometimes the prey appears to be stalking the predator.
0:32:58 > 0:33:05Grazers even taunt a hunter to make quite sure that there is no way it can launch a surprise attack.
0:33:05 > 0:33:09And at this point, many hunters would give up...
0:33:09 > 0:33:11but not always!
0:33:12 > 0:33:14An attack is now imminent.
0:33:14 > 0:33:17Sound the alarm!
0:33:17 > 0:33:20VARIOUS ANIMAL CRIES
0:33:28 > 0:33:31Now the time has come to run.
0:33:41 > 0:33:48Herbivores have powerfully muscled hind legs that give them superlative acceleration,
0:33:48 > 0:33:53invaluable if you are caught unawares.
0:34:05 > 0:34:09Once again, numbers bring safety.
0:34:19 > 0:34:24The North American pronghorn is the second fastest sprinter on the planet,
0:34:24 > 0:34:28but over long distances it's the world champion.
0:34:31 > 0:34:36But all large herbivores have to be able to run fast.
0:34:36 > 0:34:42They run on tip-toe, so that they cover more ground with each stride.
0:34:43 > 0:34:49Muscles are bunched at the top of the legs, so that the limbs are streamlined.
0:34:51 > 0:34:54Some grazers flaunt their athleticism,
0:34:54 > 0:34:59as if to say, "I'm fit, so save your energy and pick on someone weaker."
0:35:01 > 0:35:08Cheetahs may be the fastest sprinters, but gazelles are better at dodging and jinking.
0:35:10 > 0:35:14Slimline legs, however, trip only too easily.
0:35:22 > 0:35:29And having eyes on the side of your head, so that you can't see directly forward, can be catastrophic.
0:35:35 > 0:35:41Even so, herbivores manage to outmanoeuvre their enemies more often than you might suppose.
0:36:03 > 0:36:07Kicking hooves and thrusting horns are formidable weapons.
0:36:10 > 0:36:14This mother is going to defend her fawn, come what may.
0:36:28 > 0:36:32A buffalo has incautiously strayed away from its herd.
0:36:34 > 0:36:39It surely can have no defence against a group of lions.
0:36:39 > 0:36:43But the rest of the herd have noticed.
0:37:06 > 0:37:13Faced with the threat of hundreds of tons of massed anger, the lioness turns tail.
0:37:16 > 0:37:20The male lion, however, seems unwilling to give up.
0:37:37 > 0:37:43The buffalo, with their heavy armament, have won this particular battle.
0:37:43 > 0:37:48But the war on the plains is a never-ending one.
0:38:00 > 0:38:07You might think that these weapons are just a defence against carnivores, but not so.
0:38:07 > 0:38:11Their primary use is to fight one another.
0:38:11 > 0:38:16And that's the drawback of living in herds.
0:38:18 > 0:38:21The Badlands of North America.
0:38:21 > 0:38:25Bull bison are preparing for the annual rut.
0:38:28 > 0:38:33There are only a few females on heat at any one time,
0:38:33 > 0:38:37so each male tries to sniff them out before rivals approach.
0:38:37 > 0:38:42The males walk in parallel, assessing one another.
0:38:50 > 0:38:57Pumped up with testosterone, they paw the ground to show off their strength.
0:38:57 > 0:39:04They spray the earth with their urine and then roll in it, so that they reek of their own hormones.
0:39:30 > 0:39:36This combination of rolling and roaring is a clear sign that there will be a fight.
0:39:41 > 0:39:44Most contests are resolved in seconds.
0:39:44 > 0:39:49A few, however, escalate into full-scale battle.
0:39:50 > 0:39:55The attack is usually head-on. At full gallop, the impact is titanic.
0:39:55 > 0:40:02One ton moving at 30mph meeting another coming in the opposite direction.
0:40:08 > 0:40:12This male is lucky to escape a fatal stabbing.
0:40:16 > 0:40:23The largest horns in proportion to body size are carried by American bighorn sheep.
0:40:26 > 0:40:28When armaments reach this size,
0:40:28 > 0:40:33their indiscriminate deployment could be catastrophic.
0:40:33 > 0:40:38Smaller males can be warned off with a simple kick.
0:40:44 > 0:40:47But closely-matched males will have to fight.
0:41:01 > 0:41:05The rules are strict. Contestants must meet head-on.
0:41:06 > 0:41:11If contact is unbalanced, both fighters could break their necks.
0:41:20 > 0:41:25An impact like that would crush a human skull like an eggshell.
0:41:25 > 0:41:28So, how does the bighorn survive?
0:41:28 > 0:41:33Well, its skull is heavily reinforced internally with bone,
0:41:33 > 0:41:36but it also has a number of hairline cracks in it
0:41:36 > 0:41:41and these flex, so acting like shock absorbers.
0:41:44 > 0:41:51The bighorn's weapon is a battering ram, but there are also swords, scimitars and daggers.
0:41:51 > 0:41:59All are ridged and pointed at the tips and both those characteristics have important functions.
0:42:01 > 0:42:08Before any physical contact is made, the males, no matter what their species, size one another up.
0:42:14 > 0:42:18If neither retreats, horns will clash.
0:42:20 > 0:42:27The V-shaped gap between the horns is always narrower than the width of a single horn,
0:42:27 > 0:42:34so that it is not possible for a fighter to strike his opponent directly on the skull.
0:42:34 > 0:42:36Having made contact,
0:42:36 > 0:42:42the contestants wrestle and now the function of the ridges becomes clear.
0:42:42 > 0:42:49They prevent the horns from slipping and enable the contestants to test each other's strength.
0:42:50 > 0:42:57Now if there is a chance, the pointed tips will be used to stab a rival in the flank or belly.
0:43:01 > 0:43:08A competitor will not waste his energy in starting a fight if he is obviously outgunned,
0:43:08 > 0:43:10so horns are continually flaunted.
0:43:13 > 0:43:17These male topi are even putting on war paint.
0:43:23 > 0:43:26By plastering their horns with mud,
0:43:26 > 0:43:33they make themselves more intimidating to other males, and more attractive to females.
0:43:40 > 0:43:47Each in this gathering of several hundred must establish a small patch of territory for himself.
0:43:47 > 0:43:53At first, the females wander through the pasture, perhaps sizing up the males.
0:43:55 > 0:43:59And the males are torn between pursuing particular females
0:43:59 > 0:44:06and battling with one another to establish their individual stamping grounds.
0:44:19 > 0:44:22Again and again, a male has to fight.
0:44:38 > 0:44:42Eventually each male has his own patch.
0:44:42 > 0:44:48The females decide which they like best and present him with his reward.
0:44:58 > 0:45:01The mating rituals go on for many days.
0:45:01 > 0:45:06Males dare not leave their territory in case rivals claim it
0:45:06 > 0:45:10and they have to fight repeatedly to maintain their ownership.
0:45:10 > 0:45:17As the days pass, they become more exhausted and eventually they can barely stand.
0:45:31 > 0:45:36They are so tired that their normal defences are down.
0:45:36 > 0:45:42The most powerful males have claimed territories in the centre of the breeding ground.
0:45:42 > 0:45:46The less strong have to accept those on the fringes.
0:45:46 > 0:45:49And that is not a good place to be.
0:45:57 > 0:46:01In spite of the circling hyenas, the males won't leave their territories.
0:46:01 > 0:46:05If they did, they would have no chance of mating.
0:46:05 > 0:46:13But they no longer have the will or the strength to confront the hyenas, unless they are attacked.
0:46:48 > 0:46:54For most of the year, when the topi grazed in the herd, they kept watch for one another,
0:46:54 > 0:46:58but the competition to breed has changed all that.
0:47:17 > 0:47:24The dangers of eating grass out on the open plain led the topi to live in herds.
0:47:24 > 0:47:28Now the price of doing so is being paid...
0:47:28 > 0:47:31by the weaker males.
0:47:34 > 0:47:40From the topi's battle to breed to the great migrations of the world,
0:47:40 > 0:47:42the underground mines of Mount Elgon
0:47:42 > 0:47:48and the extraordinary shape and size of the wonderful creatures that made them,
0:47:48 > 0:47:53all these stem from the apparently simple act of eating leaves.
0:47:53 > 0:47:57So, as always in the Life of Mammals,
0:47:57 > 0:48:00what you eat determines what you are.
0:48:17 > 0:48:24Elephants are surely the most impressive, the most formidable of all plant predators.
0:48:24 > 0:48:28They are, after all, the biggest of all land animals.
0:48:28 > 0:48:34And yet they can suddenly appear or disappear absolutely silently in the bush.
0:48:34 > 0:48:40They're so powerful, they can flatten your Land Rover, if they have a mind to do so.
0:48:40 > 0:48:43And they're so intelligent, they have such long memories,
0:48:43 > 0:48:49and they communicate within their families in ways which we are only beginning to understand.
0:48:49 > 0:48:56Sitting in a canoe, watching elephants coming down to the river to drink is a marvellous experience.
0:48:56 > 0:49:02But to be in a cave in the pitch blackness where you can't see them,
0:49:02 > 0:49:09and yet you can hear the creak of their bodies, and that low, rumbling call, that is something else.
0:49:09 > 0:49:12And to tell you about that,
0:49:12 > 0:49:14here is Justine Evans,
0:49:14 > 0:49:21who has spent night after night in that cave in Mount Elgon with her cameras.
0:49:21 > 0:49:26It was not so much scary... I don't know even if it was dangerous,
0:49:26 > 0:49:29but it felt intimidating
0:49:29 > 0:49:35and quite overwhelming. It sounded worse than it was because of the cave walls.
0:49:35 > 0:49:42They made the sound of the elephants resonate, so I felt that they were roaring right next to me.
0:49:49 > 0:49:56There's...one, two, three, four, five...at least five in here at once, which is amazing.
0:49:56 > 0:50:00They came all the way to the back and I got all sorts of shots.
0:50:00 > 0:50:07The baby was standing in the dark, obviously really bored because it doesn't know how to tusk yet.
0:50:07 > 0:50:13He was just doing this with his trunk and going round in circles!
0:50:14 > 0:50:20The cave elephant families follow ancient traditional pathways used by many previous generations.
0:50:20 > 0:50:23There's some kind of inherited culture.
0:50:23 > 0:50:30Young calves, following in their mother's footsteps, may be too young to dig for salt,
0:50:30 > 0:50:36but they're here to learn the traditions of Mount Elgon's elephants.
0:50:36 > 0:50:43The notion that elephants might have traditions would have been unthinkable only a few decades ago.
0:50:43 > 0:50:49But since then, scientists have started to study elephants by living alongside them in the field
0:50:49 > 0:50:52and recognising each individual one.
0:50:52 > 0:50:59No-one knows them better than Cynthia Moss who's lived in Amboseli for the past 30 years
0:50:59 > 0:51:06and recognises every member of 50 families, the most famous of whom, perhaps, is Echo.
0:51:08 > 0:51:10We first filmed Echo in 1993.
0:51:10 > 0:51:15Since then, we've followed her reign as head of the herd.
0:51:18 > 0:51:20Echo is now a grand old matriarch.
0:51:20 > 0:51:25Her crossed tusks make her unmistakable.
0:51:29 > 0:51:31This is her latest grandson.
0:51:31 > 0:51:36Ella, with ragged ears, is her second in command.
0:51:36 > 0:51:41Initially, ears identified individuals.
0:51:41 > 0:51:46Their ears are never absolutely smooth along the edge.
0:51:46 > 0:51:50There's usually little nicks or holes or whatever.
0:51:50 > 0:51:54But after a while, you recognise the whole elephant.
0:51:54 > 0:51:59Wildlife cameraman Martyn Colbeck has worked alongside Cynthia.
0:51:59 > 0:52:04Together, they gained a deeper insight.
0:52:04 > 0:52:08Cynthia Moss's knowledge of individual elephants
0:52:08 > 0:52:10has been very significant for us.
0:52:10 > 0:52:14It would have been difficult for me to do it on my own
0:52:14 > 0:52:19as I did not know the individuals and how they related to each other.
0:52:19 > 0:52:23Cynthia and Martyn were accepted as part of the family.
0:52:23 > 0:52:30I think one of the most exciting things I've ever seen and filmed with the elephants
0:52:30 > 0:52:34was the birth of a calf, the matriarch's calf, in fact.
0:52:34 > 0:52:38I just never thought that we'd ever be able to film it.
0:52:38 > 0:52:45For the matriarch to trust us enough to give birth right next to us in the middle of the night
0:52:45 > 0:52:48was quite a privilege.
0:52:48 > 0:52:52And it took us several years to get ourselves into this situation.
0:52:52 > 0:52:57When the delivery finally happened, the whole family went crazy.
0:53:00 > 0:53:05They made sounds that I'd never heard elephants make before.
0:53:05 > 0:53:07They all crowded around Echo
0:53:07 > 0:53:10and it was extraordinary.
0:53:10 > 0:53:12It was a magical moment.
0:53:15 > 0:53:19When there's such a bond of mutual trust and understanding,
0:53:19 > 0:53:23the detail of the elephants' behaviour emerges
0:53:23 > 0:53:27and the drama of their lives is revealed.
0:53:27 > 0:53:31Usually, Cynthia Moss was there interpreting behaviour.
0:53:31 > 0:53:39There's a very good example of that when one of our family's calves was kidnapped by another family.
0:53:39 > 0:53:45That's a very rare bit of behaviour and I would have had no idea that that was about to happen.
0:53:45 > 0:53:53Echo gets a vicious poke in the backside when she tries to rescue Ebony from this larger family.
0:53:53 > 0:53:57The other matriarch, called Vee, is using Ebony
0:53:57 > 0:53:59to emphasise her dominance.
0:54:01 > 0:54:03But help is on the way.
0:54:03 > 0:54:10Reacting to Ebony's distress calls and Echo's alarms, the rest of the family arrive in tight formation
0:54:10 > 0:54:13and plunge into the kidnappers.
0:54:13 > 0:54:15FRANTIC TRUMPETING
0:54:24 > 0:54:26Ebony was rescued by her family.
0:54:33 > 0:54:38For some elephants, the strength of the family is even more important
0:54:38 > 0:54:43and inherited traditions are the difference between life and death.
0:54:43 > 0:54:48This is most clearly the case for the elephants of Namibia.
0:54:49 > 0:54:56They live in desert and so they're having to move over enormous distances to find food and water.
0:54:56 > 0:55:01The matriarch is like a repository of knowledge for the whole family.
0:55:01 > 0:55:05They know exactly where they need to go in order to be able to feed.
0:55:05 > 0:55:09They must have complex mental maps of an enormous area
0:55:09 > 0:55:16because the water holes are extremely isolated and they're only there at certain times of year.
0:55:16 > 0:55:21So their intelligence and mental mapping ability must be phenomenal.
0:55:21 > 0:55:27And that knowledge is passed down through generation after generation.
0:55:27 > 0:55:34So, now we know that tradition is an essential for the survival of the elephants.
0:55:34 > 0:55:40But long migratory journeys are part of the annual cycle of many plant predators.
0:55:40 > 0:55:47And it's group memory that enables some of them to make the longest journey of any land animal.
0:55:48 > 0:55:52This is perhaps the most impressive migration of all.
0:55:52 > 0:55:59Huge herds of caribou on their annual movements across Alaska and Canada.
0:55:59 > 0:56:04And using the same principle of identifying and studying known individuals,
0:56:04 > 0:56:09we can understand and film an animal tradition on a vast scale.
0:56:11 > 0:56:13Very little is known about them,
0:56:13 > 0:56:18although there's millions of them in Northern America and Canada.
0:56:18 > 0:56:23There's a scientist working with one herd of about 900,000 animals.
0:56:23 > 0:56:3025 of them are satellite collared, so that you can locate an animal in the most difficult situation.
0:56:30 > 0:56:35Once a week, he got a read-out of where those 25 animals were.
0:56:35 > 0:56:40From that, we'd look at this map about an area the size of France
0:56:40 > 0:56:47and we'd be able to tell exactly where the animals were, so we could fly ahead and land
0:56:47 > 0:56:51and film them migrating them through an area.
0:56:51 > 0:56:55Technology's opening up a whole new field of behaviour that we can film.
0:56:55 > 0:57:01One caribou tracked by satellite moved over 3,000 miles in one year,
0:57:01 > 0:57:04the record for any land mammal.
0:57:04 > 0:57:07Like some migratory birds,
0:57:07 > 0:57:14caribou may have a built-in compass to help them cross unfamiliar land on the way to their calving grounds.
0:57:14 > 0:57:19But, as with the elephants, herd traditions shape the movement.
0:57:19 > 0:57:25What they gain from living in the herd seems to be a key factor in their survival.
0:57:28 > 0:57:33In our next programme, we meet the most numerous mammals of all,
0:57:33 > 0:57:36the rodents.
0:57:36 > 0:57:43They use their chisel-like teeth in the most extraordinary ways and manage to live almost everywhere.
0:58:03 > 0:58:06Subtitles by Dorothy Moore BBC Broadcast 2002
0:58:06 > 0:58:09E-mail subtitling@bbc.co.uk