Meerkats in the Kalahari Desert. They spend the night in burrows.
They find all the food they need on the ground.
They're swift and expert runners.
Oddly enough, they also climb - and they have very good reasons for doing so.
First of all, they have to warm up in the early morning sun.
Once they're warm, it's time for breakfast.
They find that, for the most part, underground.
But if you have your head in the sand, you can't see danger approaching.
Since they have many predators, someone must always stand guard.
Sentries aren't very effective if they can't see over the tall grass,
so to get a really good view, they have to climb as high as they can.
They don't have particularly long claws or any other special climbing adaptations.
Nonetheless, they're surprisingly agile up in the branches.
They will climb pretty well anything around, if it gives them extra height.
An ability to climb is important for a meerkat on sentry duty,
but for some mammals, it's essential.
They spend nearly all their time up in the branches,
and if you do that, you really do need special adaptations.
So what kind of body does a tree dweller need?
Grasping hands, long arms to reach distant branches,
a long tail perhaps to help with balance? So nothing like this, then!
These are hyrax,
and in this safari lodge in Kenya they've acquired a taste for sunbathing.
Looking at their general body shape, you might think
that they were about as good in trees as rabbits or guinea pigs.
Actually, they're surprisingly capable of climbing around in the branches,
and the reason has to do with their very special feet.
Their rubbery soles don't look particularly special,
and you can only see how effective they are
when their owners stop lazing about in the sun and go off to feed.
Hyrax have an extremely flexible spine.
That helps them to scamper up the trunks of trees with surprising speed.
But it's their feet that help them stay up there.
Special muscles in the middle of each foot pull up the centre of the sole.
The pads are moist, so this creates a slight suction
which improves their grip, though not all that much.
Watching them clamber around like that makes me feel
I should be standing underneath with a net, in case they fall.
What is the reward for this high wire act? Leaves.
They supply the hyrax with both food and drink.
Succulent leaves are hard to find down on the ground,
but up in the branches, hyrax can get all they need for the day in a couple of hours.
So climbing trees is vitally important for a hyrax,
even if it does slip every now and then.
Fortunately, these trees are not very high, but elsewhere in the world,
there are trees that are ten times as tall as this,
and there, if you are going to be safe, you really need something better than rubbery feet.
Claws should be long and so should tails.
Tails may not look like climbing aids,
but they can be of great help in keeping your balance.
This is tropical America and these are coati.
Much of their food can be found on the ground.
They climb, primarily, for a different reason - safety.
At the first sign of danger, up they go.
These days, we too have got specialist tree-climbing gear.
Start by catapulting a fishing line over a bough, using that to haul up a rope.
Then, with clip-on hand-holds and the help of a counterweight, you can go up too.
As in all forests, the trees compete with one another to capture the sunshine.
Here in the tropics, they grow very tall in the process.
It's up in the canopy, 100 feet above the ground, that the real richness of the forest lies.
A third of the earth's land is still covered by trees of one kind or another.
So, not unexpectedly, mammals belonging to very different families
have managed to acquire the skills and physical adaptations needed
to get up into the trees to feed.
This is what most people would think of as a real forest, the tropical rainforest.
There's a greater variety of food up here than anywhere else in the natural world.
The most obvious source of food up here, of course, are leaves.
There are certainly enough of them.
The fact of the matter is that leaves aren't really very good food.
They are rather tough, indigestible, and actually don't contain much nutriment.
One mammal solves that problem not by eating more but by doing less.
The sloth moves as if it's powered by the wrong sort of batteries
and prevents itself from falling off, not by muscle-power
but by hanging from hooks, its claws.
There's a lot more than leaves to eat up here, as coatis know well.
If you're fast and agile, you can catch birds up here.
If you're not, well, some birds make their nest here,
and then eggs and chicks make a good and easy meal.
And there are brightly-coloured fruits with fleshy coverings,
sufficiently good enough to eat to persuade animals of all kinds
to swallow them and so distribute the seeds.
The coatis need little encouragement to do that.
Fruit makes up most of their diet, and it's good to grab it before it falls
and comes within reach of other fruit-eaters down on the ground.
If you're going to stay up here for a long time, you will need to drink.
That, surprisingly, is not necessarily a problem.
Sometimes it's easier to get a drink up here than it is down below.
These bromeliads, vase plants, are full of water,
and sometimes these tiny ponds contain insect larvae or even frogs.
So there's protein as well.
Woolly monkeys regularly drink from them.
So they have no need to go down to the ground and hardly ever do so.
The larder in the forest canopy is far too rich to ignore
and many mammals come up here and feed up here.
They have special climbing skills and are much more at home here than I am.
These are proper tree-climbing claws.
They belong to the sun bear of Indonesia. It also is a fruit-eater,
and it spends more of its time up in the trees than any other bear.
Bears don't have tails that might help with their balance,
but this isn't a problem to the sun bear,
as it embraces branches rather than run along them and has enormously strong forearms.
If that's the way you climb, going down is almost as easy as going up.
The South American tamandua is an ant-eater,
and like all ant-eaters, it has powerful front legs for ripping open ants' nests,
but they're also a great help in climbing.
It has a tail, and that has become an extremely valuable climbing aid.
It's prehensile - it can grip.
It is, in effect, a fifth limb.
So it can use its front legs in the same way as its ground-living relatives do.
Its tail is so well-muscled, it can support the animal's entire weight.
Which is just as well!
There are only so many ant and termite nests in any one tree,
and sooner or later the tamandua has to go and look elsewhere.
It has to leave the branches and trundle across the forest floor.
No big mammal can spend its entire life in a single tree.
They all have to move to find new sources of food.
Descending one tree, moving across the ground and climbing another
is one method, but there is another, more energy-efficient way -
to cross from one tree to another, up there.
In South America, woolly monkeys do that by using their tails,
which are even longer and stronger than the tamandua's.
A small gap like that might be crossed with the help of a prehensile tail,
but no tail is going to help with a gap of that size.
From up there they must look like an abyss,
but they are the great challenges for any tree-dweller.
Squirrels deal with the problem with dazzling ease.
They're such lightweights,
they can race along the thin twigs at the very far end of the branches.
And they're spectacular jumpers.
Their powerful hind legs provide the thrust.
Their long tail acts as a rudder.
Their shorter front legs serve as shock absorbers to cushion the landing.
Superb sight enables them to judge distance with great accuracy,
an essential ability when racing along this three-dimensional highway.
They are at their most acrobatic during the mating season,
when males start to pursue the females.
One male may begin the chase, but others quickly join in.
Eventually, one wins.
As soon as he's claimed his prize, the chase will start over again
and the female may mate with up to eight different males in a single day.
A gap this size is just too big, so a grey squirrel, like a tamandua,
often has to come to the ground if it's to visit all the trees in its range.
A grey squirrel can leap eight feet,
but there's another tree-dweller that can leap much farther than that.
Although it's no bigger than my hand,
it can jump from this tree to that tree over there,
more than fifty feet away.
An astonishing distance! To see how it does it, we'll have to come back at night.
Since they have an acute sense of smell and love seeds and nuts,
maybe these will tempt one down from the tree tops.
They are flying squirrels.
How do they fly? Just watch.
Maybe ''gliding squirrel'' would be a more accurate name.
They're nonetheless astonishing.
That furry membrane stretching between wrist and ankle makes an efficient aerofoil.
Flying squirrels are not territorial
and as many as half a dozen can be foraging in the same area of woodland.
Although this little squirrel may have travelled a very long distance
in order to get to this valuable source of food,
it's such an expert glider, it's done so with a minimum of effort.
In forests like this, where food sources are often widely dispersed,
the ability to travel fast and far, but with little effort,
is a very valuable ability indeed.
There are few gaps in these forests that defeat them,
but to cross really long distances they do need height.
They steer partly with their tail and partly by moving their outstretched legs
so that they vary the tension of their gliding membrane.
You can see that they can steer
when one squirrel uses the same take-off point
but glides away to land on different trees.
Even so, they're not agile enough in the air to escape birds of prey,
so during the day they sleep in holes and only emerge when it's dark.
Gliding from branch to branch
was a comparatively small step for tree-living mammals,
but there was one group of them that made a truly gigantic leap.
Their arms changed into wings.
The shoulders, elbow and wrists remained much the same,
but the hand and fingers changed dramatically.
Flying foxes - fruit bats in Australia.
They and their insect-eating cousins
are the only mammals that have developed true powered flight.
They're so big that they can't roost in holes. Instead they sleep out in the open
in colonies that may be hundreds of thousands strong.
The thumb on each hand is free of the wing and has a hooked claw.
Using that and the claws on the toes,
fruit bats are surprisingly nimble, clambering about in the branches.
(SCREECHING CHATTER)
Wings may have solved the problem of getting from one tree to another,
but landing is still a challenge.
As a fruit bat approaches its chosen perch, it goes into a glide.
Then it lowers its toes and hooks them onto a branch.
This is a textbook example of how it's supposed to be done.
But some perches are more difficult to reach than others.
Wings need regular grooming.
They are also very delicate, but small tears quickly heal.
The wing membrane is among the fastest-growing of all mammalian tissues.
They also fan their wings to keep themselves cool.
It can be very hot, hanging unprotected in the baking sun.
Take-off too requires a special technique.
Two or three wing beats lift the body to the horizontal
and only then should the feet be unlatched.
That way you don't lose too much height.
It's hard work, particularly if you're carrying a baby
which is a third of your own weight.
Once in the air, fruit bats are extremely strong flyers.
(SCREECHING CHATTER)
They can travel great distances,
as much as thirty miles - fifty kilometres - in a single night,
if that's necessary to find food.
They may have lost a lot of moisture, hanging around in the midday sun,
so their first call is often to a nearby lake to get a drink.
They do this in a rather unusual way. First, they dip their chests in the water.
Then they return to their roost and lick the moisture from their fur.
But there are hazards.
Crocodiles.
The bats only touch the water for less than a second
and usually the crocodiles are not quick enough to catch them.
But if one miscalculates and comes down on the water,
it's a different matter.
They're surprisingly good swimmers.
The worst danger comes when they get to land.
Without being able to drop into space as they can from a perch,
they find it very difficult to get airborne.
Now the crocodiles have the advantage.
But a few individuals lost to crocodiles makes little impact on the bat colony.
This roost alone contains a staggering five million.
Living together in these vast numbers brings several important advantages.
Flying foxes collect fruit and nectar of many different kinds.
Knowing which species of fruit tree is in season at any particular time
is not easy, and some are unpredictable.
If a few individual bats return smelling of a particular fruit,
the news that this food has just come on the market
spreads quickly through the whole colony.
Each bat knows where trees of the various species can be found,
so the next night it'll go to its own favourite patch to collect the new fruit.
That is why the whole five million don't follow one another to the same tree.
Huge wings may be good for long-distance flying,
but they don't give great manoeuvrability in the air,
and when the bats return in the dawn, hunters are awaiting them.
Eagles know where a bat's blind spots are and attack from below.
Powerful though eagles are,
fruit bats are big animals and a hit isn't necessarily a kill.
Raids like these are another reason why an individual bat
finds it an advantage to roost in a colony.
Since it's surrounded by tens of thousands of others,
there's a good chance that an eagle will pounce on someone else.
Most colonies have a resident pair of eagles that nest nearby.
A breeding pair will take half a dozen or so bats a day.
But that still makes little impact on bat numbers.
Skilled though the eagles are in taking bats on the wing,
their most successful strategy is to snatch them as they hang in branches.
There's another way of getting around in the treetops.
Instead of having fingers that are greatly elongated and form struts for a wing,
they can be very small, muscular, and give you an extremely powerful grip.
The mammals that did that are of particular interest to us
because they contain our earliest ancestors.
Most of them are small and nocturnal
and the best way to find them is with a torch, like this.
Highly reflective eyes, caught in the torch's beam.
They belong to a slender loris.
It's a primate, a primitive relation of the monkeys,
and it lives in southern India.
Using a bright light may be the best way of finding a loris,
but it's not the best way of discovering how they behave naturally.
To do that, you have to turn off your lights.
Infra-red cameras give us a rare chance
of watching a slender loris at close quarters without disturbing it.
It's moving so quietly that if it wasn't for this monitor,
I wouldn't even know that it was just over there.
Lorises have greatly elongated thumbs and have lost their index fingers,
so their grasp is wide enough to encircle quite stout branches.
They can hold on so tightly that it's almost impossible
to detach one from a branch against its will.
It's the talent for gripping, together with a long reach,
that enables them to deal with that problem of crossing from one tree to another.
That's what it's after - berries.
There's another here. Lorises live in small groups of four or five.
Something seems to have caught this one's eye.
Perhaps it's our dim infra-red light.
It's frozen motionless.
That's standard alarm behaviour from a loris.
It can't move fast, so it stands little chance of out-running a predator.
Instead, it simply stops and hopes that nobody will notice it.
Now it's off again.
It's scent marking.
That little drop of urine will tell others that it's here.
It washes its hands in urine so that it leaves a trail of smelly footprints.
Some people think that the urine gives the animal a better grip.
It's certainly quite sticky.
Its eyes both face forwards, giving it the stereoscopic vision
necessary to judge distance accurately.
It hunts not by speed but by stealth.
Silence, acoustic camouflage, enables it to catch its prey unawares.
Gripping feet, like prehensile tails, leave hands free for the pounce.
That was a grasshopper.
Now it's found a stick insect.
This is a mantis.
Mantises defend themselves in two ways -
either by camouflage or aggressive display like this.
Neither of them seem much good against a loris.
Only one creature stands a chance of removing something from the grasp of a loris...
and that is another loris.
Africa has got its own similar creature,
only a very much more lively and athletic one.
The lesser bush baby. It's probably the most numerous primate in all Africa,
but you seldom see it because it only comes out at night.
They have a regular pathway through these trees, which they also mark with their urine,
so you can predict that they will go from one tree to the other.
They're related to lorises and physically very similar,
with grasping hands, stereo vision and large ears.
But their way of getting around is completely different.
They hunt not by stealth but by speed.
If pressed, they can jump thirty times their own body length.
This one is carrying an infant.
A leap like that...is nothing to a bush baby.
Before one takes off, it moves its head from side to side,
working out the best place to land.
That's important, because many of these trees are very thorny.
Bush babies of one species or another
have colonised almost every type of forest here in Africa.
Millions of years ago, ancestral bush babies even spread beyond the continent.
Somehow or other, perhaps on a floating log, they reached the island of Madagascar.
Here there were neither predators nor competitors,
and here they diversified into an extraordinary range of species
which now exploit every environment on the island.
They are the lemurs.
(CRIES OUT)
The most specialised of them is the golden bamboo lemur.
It was discovered only recently and it lives on a part of the bamboo
that would be fatal to most other animals.
Bamboo pith is full of cyanide, and the golden lemur
eats twelve times as much as would normally kill an animal of its size.
Other Madagascan plants defend themselves in a different way.
Didierea is covered with ferocious spines,
yet it is the chosen home and feeding grounds of another lemur, the sifaka.
Clambering about here requires some very delicate footwork indeed.
Mother's tail clearly makes a better handhold for a youngster,
but even at this age, a young sifaka is able to negotiate the spines.
Collecting didierea leaves and flowers - and they're the sifaka's main food -
looks even more hazardous than travelling around through its branches.
When sifakas decide to move, they can travel very fast indeed.
They use the same basic method as bush babies but do so with such speed and confidence
that they seem almost to bounce from trunk to trunk.
Only in slow motion can you see just how accurately they land
and how instantaneously they're able to take off again.
But given the chance, they assess their jumps with care.
Take-off has to start sideways-on to the line of flight,
so they have to rotate their bodies in mid-air.
Then those hind legs, having kicked off,
have to be swung forward to act as shock absorbers as they make contact.
Their back feet are long and narrow, with an enormous big toe,
so that they can lock on to a trunk as soon as they hit it.
Then, within seconds, they are off again.
A female can even do all this while she's carrying a baby.
Down on the ground, however, the method doesn't work quite so well.
Extremely long legs and very short arms make it impossible to run on all fours,
so once again it has to be jumping,
but with no vertical trunk to push away from, the leaps are rather shorter.
Back in the trees, they can travel at speed again,
and they need to, for they have a savage enemy.
The fossa.
Its speed through the branches rivals that of the sifakas, but its technique is entirely different,
for it's not a primate, with jumping ancestors, but a kind of giant mongoose,
and it's still a four-footed runner.
Nonetheless, they're a close match for one another.
But when it comes to the long jump, the sifaka wins.
A four-footed runner can't match that.
It's caught the scent of something else, a female who is ready to mate.
She's taken up residence in a tree and there she's holding court.
She will attract several males. There's going to be strong competition.
An unusually long tail helps in maintaining balance,
and they manage to negotiate surprisingly thin branches.
The female will decide who she mates with,
and drives off those in whom she is not interested.
(SQUAWKS AND SCREECHES)
Mating itself is a noisy affair and is made more difficult, doubtless,
by having to balance on a branch while it's going on.
(CRIES AND GROANS)
(CRIES CLIMAX)
Few other hunting animals can match a fossa for speed through the treetops,
and few can descend head-first like this.
The fossa manages to do so because it has very flexible ankles
that allow it to twist its feet round to point backwards.
To find the supreme tree-traveller, we have to go to another continent.
We have to climb into the canopy of the forests of south-east Asia.
(CREATURES CALL OUT)
This forest is home to the fastest of all the flightless inhabitants of the canopy in the world.
It's so swift and so agile, it's capable of catching birds in mid-air.
Gibbons. Not monkeys, but small apes.
Their long jump record is about the same as a sifaka, around 40 feet,
but they can move at even greater speed.
They're such skilled acrobats that they can change direction in mid-flow.
We may be distantly related to the lesser apes, but when you watch gibbons up in the branches
you realise how ill-equipped we are for a life in the trees.
Our forearms are too short, our thumbs are too big, our shoulders and hips too inflexible
and our eye-to-hand coordination, compared with gibbons, is very poor.
They have one characteristic which we - and indeed all other primates - lack;
that is to say, a ball and socket joint in their wrists.
It's that that allows them to perform these fantastic aerial gymnastics.
Hurtling through the branches hand over hand is the gibbons' standard way of getting around.
Their unique wrist joint enables them to rotate the body around the hand and not the shoulder,
and that saves a lot of energy.
But travelling at this speed can be hazardous. Branches may break, jumps may be misjudged.
Researchers estimate that most gibbons fracture their bones at least once in their lives.
And fatal falls are certainly not unknown.
Life in the trees is a dangerous business. One serious mistake is likely to be your last.
Mankind's success started when its feet hit the ground and it stood up on its hind legs.
But the coati and the hyrax, the tamandua and the gibbon
are proof that there is a very good living to be had up there.
(WARBLED CRY)