[vultures hissing] [meerkat squeals] [blue wildebeest bellows] [calming music] [vulture squeals] [calming music] [gentle music] - In desert sand dunes like this it's easy to understand how the term lifeless desert crept into our language.

It's much harder to understand how any organism could survive such an arid, hot and hostile climate.

Hi, I'm George Page for "Nature", and the more we learn about deserts the more we realize there are probably no truly lifeless deserts on earth, we'd have to go to the moon or another planet to find a desert with no life at all.

On our planet, wherever deserts are found, some form of life will be there too.

In fact, the desert environment probably represents the greatest challenge to the incredible adaptability of life on earth.

This week we go to the exotic Kalahari desert in the Southern African country of Botswana, where an amazingly rich and diverse community of plants and animals has evolved over the centuries.

[insects chirping] [hyena chatters] Night brings relief from the oppressive heat.

Lack of water and food has forced many of the larger animals to move on, only scattered bones leave evidence of their passing.

The brown hyena lives here, this is its refuge, here no competitors can drive it out, it has adapted, it can eat even the oldest bones of those the desert has killed.

[insects chirping] [hyenas whooping] It is a survivor.

[gentle music] [birds chirping] [gentle music] Searing heat and extreme dryness have dictated the pace of evolution for plants and animals in this wilderness, the largest unbroken mantle of sand on earth.

[gentle music] Kalahari means wilderness, for the Kalahari is not a true desert, but arid grassland growing on ancient sands.

These sands dominate Southern Africa, stretching north to beyond the equator.

Within the last 18,000 years, a change of climate has brought warm rains to Central Africa.

Now, once restricted rainforests are widely spread on the sands of the Congo Basin, to the south as rainfall diminishes woodlands and grass have taken root, and today, although the sands remain exposed in Southern Africa, it's only in the far southwest that unpredictable rains preserve near desert conditions.

[gentle music] Endless parallel dunes are bisected by fossil river valleys.

[gentle music] Time stands stand still here, isolated acacia trees mark the ancient water courses, their deep roots tap a hidden river flowing 100s of feet underground.

[birds cooing] There's no water on the surface, temperatures soar, and the sands heat to a blistering 150 degrees Fahrenheit.

The dry season is unrelenting in its harshness.

[animals squealing] Here, the scavenger, not the hunter is successful.

[vulture squeals] Usually Vultures are first on the scene.

[vulture squeals] Soon, they're followed by the Jackal.

[vultures squealing] Honey badgers do well here, their sharp claws easily rip through the hard river floor in their constant search for food.

[honey badger scratches] Again, the jackal, Some prey might escape the badger.

[vultures squeals] [honey badger growls] [birds chirps] Both animals have an ancient lineage and are still found throughout most of Africa.

[vultures squeals] For the brown hyena it's different, in the past as the desert shrank the hyena was forced to retreat with it.

Now they're found only in Southern Africa.

[vultures squealing] Many of the Kalahari's larger animals, like the wildebeest cannot live in only one place, they must wander with the seasons, endlessly searching for food.

Above the valley in the dunes browsing animals must depend on the tough drought resistant vegetation, which binds the dunes and holds them in place.

[hooves clopping] The gemsbok is a species of oryx, when the arid lands of Southern Africa were one with those of the north, its ancestors moved south.

[hooves clopping] In most years, some rain does fall, usually as erratic, isolated thunderstorms, bringing only temporary relief.

[thunder rumbling] [rain pattering] Giant bullfrogs emerge with the first heavy shower.

Anticipating enough water to breed, they've survived the heat and drought of the dry season in a cocoon below the riverbed.

[rain pattering] [bullfrogs bellowing] The depressions filled with water, but the lakes are deceptive, likely to disappear as quickly as they formed.

[water burbles] [gentle music] The water attracts springbok.

[gentle music] [insects chirping] [birds chirping] [calm music] The water evaporates almost immediately.

Fooled by the brief flood, the bullfrogs must dig their way back into the mud, slow their bodily processes and renew their cocoons, to wait perhaps for several years for the next rains.

[insects chirping] But the storm has brought a change, in the dune melon seeds are germinating, the first stage in a cycle essential to the survival of many of these plants and animals.

For a moment, life is easier.

[insects and birds chirping] The lions of the Kalahari have survived without water for eight months, the drought drove them to forage over a huge territory, 100s of square miles.

[insects and birds chirping] Now the lion's prey has concentrated where the rains fell, the lions territory has contracted and the hunting has been easier.

[insects and birds chirping] [bird squealing] [lion grunting] [birds squealing] As the first flush of grass brings life to the fossil river valleys, the springbok move down from the dunes.

They need the minerals in these young grasses.

[springbok pronks] Behind them the dunes are flowering.

[birds squealing] [insect buzzing] And with the flowers briefly come the insects, soon smothered in pollen as they devour the petals.

[birds chirping] Pollination still takes place because the reproductive parts of the flower are not eaten.

Insects must feed quickly, for they, along with the plants, must complete their lifecycle before the Kalahari dries out again.

Millipedes too are drawn to the new source of food, but unlike the beetles they completely destroy the flowers.

[birds squealing and chirping] Even the antelope, like the red hartebeest are attracted and begin to congregate in the flowering dunes.

It's the successful pollination of these annual plants which makes life possible for the animals.

The plants must live out the rest of the year as fruits or seeds, vital food for animals during the long months of drought.

[birds chirping] Tsamma melons are the most important food source.

[birds chirping] In the [indistinct] pollen is scattered, eaten, and dispersed to other flowers.

[birds chirping] [insects buzzing] But for the Kalahari, this food supply is a luxury which explodes into abundance only when conditions are right.

As important are the perennials, plants like the rhigozum which actually hold the dunes together.

They and the grasses are the living backbone of the Kalahari, vital for the animals during the coming drought.

[gentle music] There are advantages to being a larger antelope in the Kalahari.

For most of the year, the hartebeest subsisted on scrub grass, they can digest it efficiently.

They have a much slower metabolic rate than the smaller antelopes, like the tiny steenbok.

Because steenboks have small mouths they select much higher quality food, such as the sprouting young buds of rhigozum which contains enough moisture to allow steenboks to live permanently in the same area.

Springbok, too, browse on young buds.

Grasses flourish under the hot sun in the valleys, their flowers are pollinated and will soon set seed.

[insects chirping] [gentle music] Even when the perennial grasses dry out they make good grazing for antelopes and their calves, they crop them right to the ground but the grasses survive as roots.

[insects chirping] The dunes still holds small fox of butterflies, lingering migrants.

Beside them, the tsamma melons are maturing, storing huge reserves of water which will attract the seed dispersing animals in the months to come.

[birds cooing] The unpredictable character of the Kalahari and its unreliable supply of nomadic prey has even restricted Africa's most successful and adaptable large predator, the spotted hyena.

[hyena scratching] It's at the den that the young hyenas learn their social skills.

[birds cooing] [hyenas laughing] At times spotted hyenas are solitary animals but often they work together as a clan.

[hyenas laughing and scratching] With night approaching adults visit the communal den, after dark they will gather with other adults for the hunt.

[birds chirping] [hyena grunts] [hyena yawns] [gentle music] [hyenas laughing] [gentle music] When there are young to look after, porcupines move around as a family emerging from their burrows to forage over large territories each night.

They survive the drought by feeding on roots and [indistinct].

Now large nutritious fruits such as tsamma melons will replenish their reserves and carry them through the coming drought.

[porcupine moans] [hyenas laughing] With their quills raised they stand as much as three feet high, the largest rodents in Africa.

[hyenas laughing] Brown hyenas also feed on melons, they disperse the melon seeds which pass through their digestive systems intact, and usually well away from seed eaters.

[insects chirping] [hyenas laughing] They return repeatedly.

[hyenas laughing] [hyena grunts] It's safer to eat elsewhere but frustrating to leave good food behind.

[insects chirping] [hyenas moaning] Night has brought a change in the spotted hyenas, there's tension and excitement in the air as the clan gathers to reinforce boundary markings by leading scent on grass dogs.

[hyena groans] The female's clitoris perfectly resembles the male's penis, she even has a mock scrotum.

Because of this, for a long time hyenas were thought be hermaphrodites.

Genital display is used in appeasement, aggression is suspended in favor of satisfying curiosity.

Investigation of each other's hindquarters is a much safer means of recognition when they meet, than a head-to-head confrontation with powerful and unpredictable jaws.

The structure of the clan is flexible, when food is scarce individuals will often hunt or scavenge on their own.

Now that food's abundant, they come together.

[hyena whines] Unlike spotted hyenas, brown hyenas are almost always solitary hunters and scavengers.

Occasionally they'll appropriate kills from other animals, even leopards.

[insect chirping] [hyenas whining] The brown hyena's ability to live off small amounts of widely scattered food enables it to survive here, but there's another reason too, elsewhere spotted hyenas are dominant and would normally drive brown hyenas from their range; but the Southern Kalahari supports a very small population of spotted hyenas, so, here, although the two carnivores may meet it's so seldom that they can coexist.

The spotted hyenas also show an interest in the leopard, it's a competitor for the limited food and they won't tolerate the leopard's presence.

[insects chirping] [hyenas groaning] [loud thud] [insects chirping] They've caught the scent of their prey, it's several miles off.

Now the hunt begins.

[hyenas groaning] [animals galloping] The prey is a young gemsbok.

[animals galloping] [hyena groans] Opportunistic Jackal soon arrive at the kill.

[hyena growls] The hyenas eat almost everything, bolting their food at great speed.

Their huge stomachs enable them to eat as much as 30 pounds of meat in a single night.

As well as killing large healthy animals, they kill the weak, the diseased, and the injured, and scavenged the dead of almost any animal.

[hyena growls] It's their extraordinary flexibility as hunters and scavengers, which has established them as Africa's most successful large carnivores.

[hyena growls] [hyenas moaning] The kill has taken them many miles from the den, with heavy stomachs they're unlikely to return there tonight, and will rest up nearby.

[hyenas groans] Winter comes silent and freezing, even to Southern Africa.

[gentle music] [honey badger scratching] Because of the freezing temperatures, many of the desert's night animals like the honey badger now must forage during the day.

[honey badger scratches] [meerkat barks] Suricates are constantly on the alert for potential danger.

They're members of the mongoose family, strictly daytime animals, and unlike the honey badger they will only leave the shelter of the burrow when it's warm.

[suricates chattering] Many of the Kalahari's residents live in burrows, including the strange looking elephant shrew with its trunk-like and permanently twitching nose.

Elephant shrews are one of the Kalahari's most primitive animals, they've survived unchanged for millions of years.

Frost has killed most of the grass, switching from their usual nocturnal foraging to avoid the cold, harvester termites are at work.

Their heads are black because of a special pigment which protects them against the harmful effects of the winter sun.

[termites scurrying] Grass is food for the colony and the stalks are dragged down into the nest.

Sometimes it's one or 200 feet underground, where there's water.

The sudden appearance of termites during the day produces a new supply of food for the shrew.

She stores them in cheek pouches to feed her young in the burrow.

[elephant shrew scurrying] The abundance of food tempts the barking gecko to leave the security of his hole too.

[gecko scurrying] [weavers chirping] Social weavers also take advantage of the dead grasses.

Stiff and coarse, the grasses are especially suitable for building the weaver's remarkable colonial nests.

[weavers chirping] There may be as many as 50 nesting chambers here, all woven under one huge roof, and with as many as 300 birds in residence.

[weavers chirping] Ground squirrels often share burrows with the suricates.

They're both under the threat of attack from birds of prey and other predators, and they benefit from each other's constant vigilance.

[squirrel bugles] Food is scarce at this time of year.

[twigs crackling] The freezing temperatures keep many animals underground.

For a goshawk, following a honey badger in order to steal tidbits is a way to survive during this difficult time.

[honey badger scratching] [feet pattering] [wings flapping] Barking geckos make up a large part of the badger's diet in winter.

Once the badger's out of the way the goshawk seizes anything he's missed, this time it's a mouse.

[thud] The honey badger is not deterred by a few setbacks in his relentless search for food, he detected a skink hiding under the bark of this tree.

[tree bark crackling] [thud] [tree bark crackling] [honey badger scratching] In the dunes, one of the few fruits to have survived the winter frost is the tsamma melon.

Already broken open by the porcupines and the brown hyenas, now they provide food for the ground squirrels.

They're attracted by the nutritious seeds and the moisture, over 90% of the melon is water.

[birds chirping] [animals scurrying] Fruit eating birds like the red-eyed Bulbu soon discover the open melons.

[birds chirping] Four striped mice feed on the melon seeds, neither the squirrels nor the mice benefit the melons, they destroy the seeds and it's up to other animals to disperse them.

[seeds crunching] Suricates lookouts are constantly alert for danger.

[suricates chattering] The rest of the group forage for beetles and millipedes.

[suricates chattering] [suricates scratching] [suricate groans] Suricates are able to see and distinguish dangerous birds of prey at a great distance, and a high-flying eagle prompts a rapid retreat to the burrow.

[suricates scurrying] [hooves clopping] [wildebeest bellowing] What little relief the storms brought has long gone.

As the dry season lengthens wildebeest and gemsbok disperse into the vastness of the dunes, seeking food.

[insects chirping] [hooves clopping] Now the heat is becoming intolerable.

[eerie music] Quite suddenly in the fossil river valleys the acacia's flower.

[calming music] Since they have permanent access to underground water, it's the lengthening of the day which has triggered their flowering.

[birds chirping] The pygmy falcon is Africa's smallest bird of prey, is well adapted to the Kalahari, feeding mainly on skinks and sand lizards.

[birds chirping] It nests in an empty chamber of the social weaver colony.

[birds chirping] The falcon rarely interferes with the weavers and ignores them as it feeds its young.

[birds chirping] As the dry season continues, starvation and disease are the main threats for the animals of the Kalahari.

[flies buzzing] [insects chirping] [wildebeest bellows] Wildebeest, always on the move, suffer more from the rigors of the climate than from predators.

[wildebeest bellows] [vultures squealing] Again, the sand is becoming impossibly hot, even vultures suffer and seek out the shade of acacias.

[vultures squealing] Life is almost impossible for the lions now, starvation is a constant threat.

[insects chirping] [lion growls] The king of beasts must scavenge to survive.

[bones cracking] [lions growling] [pattering feet] [bones cracking] [wildebeest bellows] [gentle music] [insects chirping] [hyenas laughing and chattering] The lions are joined by stumbling cubs.

[lion growls] They're starving.

Normally the adults make them eat last, now they're tolerated but it may be too late.

The Kalahari exacts a heavy toll on baby lions, In some years all of them die.

[lion growls] Brown hyenas are more successful, they're able to adapt and take advantage of any food available.

And what isn't eaten immediately is stored and eaten later.

[insects chirping] [hyenas chattering] [sand shuffling] [birds chirping] [hyenas chattering] A new day brings no relief.

[flies buzzing] [feet pattering] Brown hyena cubs have a better chance, they stay at the den for more than a year.

[hyenas scurrying] [birds chirping] [feet pattering] [birds chirping] During the first few months they're suckled, later when they're weaned the parent will bring solid food back to the den.

[hyenas chattering] And so, in Africa, Darwin's theory is played out in a dramatic setting, the fittest will survive.

[birds chirping] And so will the tsamma melon, dispersed naturally by the brown hyenas.

The seeds and the whole Kalahari await the rains.

[gentle music] [gentle instrumental music] [upbeat music]