[Narrator] Every continent north of Antarctica has grasslands.

They once covered 25% of the Earth's land surface, creating prime habitat for herbivores.

In North America, these sweeping, evocative landscapes are called prairies.

In Africa, savannahs.

And in Australia, they're simply referred to as the outback.

Despite intense and ongoing pressure to turn these native pastures into farmland, some of the world's grasslands have managed to retain their integrity and much of their original wildlife.

These extraordinary open-air theaters provide front-row seats for us all to enjoy what is arguably the greatest show on Earth.

Tanzania is a relatively small country in Africa, but it has some of the largest herds of wild animals on the planet.

And these herds are easy to encounter as they sweep across the vast savannah grasslands.

Tanzania sits just south of the equator so there's no real winter or summer, just wet and dry seasons.

The rains come twice a year, a short burst from October to December and a longer, stronger wet season, from March to June.

Ngorongoro Crater, an ancient volcanic caldera, sits at the heart of Tanzania's wildlife extravaganza.

It presents a striking landscape, created by a cataclysmic explosion that occurred over three million years ago.

The original volcano would have been as high as Kilimanjaro, the loftiest mountain in Africa.

But after it erupted, it collapsed, leaving behind this remarkable sanctuary known locally as The Garden of Eden.

The crater sinks to a depth of 2,000 feet, creating a natural enclosure.

A giant bowl, containing an alphabet soup of Africa's wild animals, from antelopes right through to zebras.

In all, 25,000 large animals, and at least 100,000 smaller ones, co-exist here in ecological harmony.

Ngorongoro Crater is the perfect place for spotting what the safari guides call the big five.

Africa's largest and most charismatic grassland animals.

The lion.

The leopard.

The elephant.

The rhinoceros.

And the cape buffalo.

Lions are the only big cat to live in social groups.

A pride of lions is an extended family with about 10 females and their young.

As the cubs grow, young females will stay with the pride, but by three years of age young males leave the group, to find a pride of their own.

Becoming part of a new pride is no easy feat, for the dominant male in the group will fiercely defend his territory from newcomers.

He'll mark the boundaries with urine, roar menacingly, and chase off any intruders.

Not an easy job as a single territory can be over 250 square kilometers.

Once a young male is sexually mature, he is ready to challenge the dominant male for the right to take over his pride.

Typically, tenure of a pride lasts around two to three years, giving the dominant male the exclusive right to every female in his harem.

Female lions do almost all the hunting.

Many of their prey animals can run faster and further, so to effect a kill, lions need to work as a team.

They'll take their time stalking their prey.

Often the pride will split up, so the escaping prey runs straight into an ambush.

There's a strict pecking order when it comes to eating, and so cubs have to make do with the leftovers.

After a good meal, lions may sleep for up to 20 hours.

A rite of passage for groups of young Maasai men has always involved the hunting and killing of a lion.

But here in Ngorongoro, times have well and truly changed.

Now these Maasai warriors are being employed by local experts to help protect the lions, using science and traditional knowledge to manage and monitor these magnificent animals.

While lions have evolved to be social, leopards are the loners of the African big cat world.

They spend much of their time hanging around in trees and are mainly nocturnal.

During the day, the dappled light in the branches allows the leopard with its spots to blend in.

Camouflage gives the leopard the upper hand when it comes to hunting.

Of the big five in Ngorongoro, they are definitely the hardest to encounter, requiring a mix of patience and luck.

But the payoff is well worth the effort.

Leopards are incredibly strong with powerful jaws.

A single animal is able to haul a large carcass right up into the tree, so it can eat in peace; a handy trick, as prowling hyenas and lions would otherwise help themselves to a share of the kill.

The athletic prowess of the leopard doesn't stop at tree climbing and weightlifting.

They are excellent swimmers, fast runners, and can jump up to three meters in the air, the Olympic pentathletes of the grasslands.

A single leopard will occupy a territory of up to 75 square kilometers.

One male will choose a territory that overlaps with a few female territories.

In this way, he has a range of choices when it comes to mating season.

The largest of Ngorongoro's big five is the largest animal on land--the African elephant.

These awe-inspiring creatures live in herds of up to 100.

They are sociable animals that spend a great deal of time with their families, roaming the grasslands, looking for water and food.

And it goes without saying that an animal of this size needs to eat quite a lot.

One adult will easily consume over 300 kilos of grass, leaves, and bark in a day, so a herd like this needs an enormous area of land to survive.

Many of the herds at Ngorongoro choose to live on the crater rim, where the air is cooler and the opportunity to graze expands beyond the old volcano's boundaries.

The other great grey grass-eater in Ngorongoro is one of the most endangered big animals in Africa.

The rhinoceros.

There are two species of rhino in Africa: the black rhino and the white rhino.

Confusingly, these rhinos are neither black nor white, rather a very similar shade of grey.

Rhinos are short sighted, so there's a good chance of spotting them in Ngorongoro before they spot you.

Like many animals with poor sight, rhinos compensate with excellent senses of smell and hearing.

Despite their bulk and relatively short legs, rhinos are impressive runners.

They can easily get to speeds of 50 kilometers an hour.

Both species are endangered, due to the continued demand for rhino horn.

It is mistakenly believed to be an aphrodisiac, fetching around $60,000 US dollars per kilogram on the black market.

Rangers who have dedicated their lives to ensuring the survival of rhinos in the wild are often forced to take somewhat drastic measures to thwart the efforts of poachers.

This can include removing or dyeing a rhino's horn so it's no longer of value to the poachers.

When conservationists became aware of the dwindling numbers of rhinos in the wild, they moved a number of individuals to Australia.

They are thriving now, in open-range style zoos, breeding generations that could, in time, be released back into the wilds of Africa.

The final member of the big five in Ngorongoro is the cape buffalo.

They won't hesitate to take on and slay a lion.

In Ngorongoro in a good year, a single buffalo herd can contain over 500 animals.

Those lethal horns are the reason these animals are so well respected by even the most skilled predators.

Both female and male buffalo have horns.

They grow from a central boss on the forehead which acts like a powerful battering ram.

There is one animal, however, that's safe in the cape buffalo's realm.

The ox-pecker.

This elegant bird will happily ride around on the back of a buffalo all day, eating ticks, mites, and other parasites that would otherwise irritate the buffalo.

The cape buffalo is the only member of the big five that is not endangered, but they do need huge amounts of food and a good ten and a half gallons of water a day to survive.

And fortunately in Ngorongoro Crater, there seems to be enough of both to go around.

North America's version of the cape buffalo is the mighty bison.

They once roamed across the grasslands here in massive herds, migrating between their summer and winter pastures.

But hunting on an unprecedented scale during the 19th century brought them to the brink of extinction.

Some 50 million bison were killed, reducing their numbers to just a few hundred individuals.

Here in Yellowstone, the oldest national park in the world, bison are well protected, so, their numbers have slowly rebounded, in step with other herds across the country.

There are now half a million bison living in reserves and commercial ranches.

The bison is the heaviest land mammal in North America and seriously impressive to encounter in the wild.

Full-grown males can be over two meters tall at the shoulder and weigh over a ton.

Outside the migration and mating seasons, these animals prefer to live in smaller groups, mostly females and their young, with a dominant male.

During the summer mating season, the groups come together and the males do what so many herding males do: fight for supremacy.

Fortunately, a lot of this is sabre rattling, and despite the animals' formidable power, injuries are not common.

Competing males also make Earth-shattering bellows.

And surprisingly, recent data from scientists suggests that the females appear to favor males with a quieter bellow.

These huge animals spend a lot of time grazing and chewing their cud.

Grass and herbs are top of the list of food favorites, but shrubs and twigs also fit the bill.

The cowbird is North America's version of the African ox-pecker and they've become the bison's regular companions.

Insects and parasites are commonplace on the hide of the bison, so the cowbird receives regular sustenance in return for the free cleaning service.

On May the 9th, 2016, President Barack Obama signed the National Bison Legacy Act, formally recognizing the bison as the official national mammal of the United States.

A fitting tribute to one of the most impressive grassland animals in the world.

Another amazing animal to encounter on the prairies of North America is the pronghorn.

The second fastest animal on four legs.

Having survived the last ice age, the pronghorn has not changed its behavior, habits, or good looks, since it first raced through the great southwest some 30,000 years ago.

Pronghorns are not technically antelopes, as they have quite a different horn structure.

But they fill the same ecological niche.

These impressive animals can reach speeds over 80 kilometers an hour and have exceptional endurance.

These herds migrate around 300 miles every year in order to survive.

One of the longest migrations by land animals in the world.

The main migration south takes place in the autumn when the pronghorns need to move out of the Grand Teton Mountains as the snow approaches.

They spend the winter in Wyoming before following the retreating snowline north to their mountain grasslands in the spring, in time to breed.

They are incredible to encounter during the migration season, as they travel in large herds.

Pronghorns are well equipped for running.

They have a large windpipe, heart, and lungs.

And they can outrun all of America's key predators, including wolves, bobcats, and cougars.

Fortunately for the pronghorn, the only animal it couldn't possibly outrun lives on another continent.

The cheetah.

The fastest land animal on the planet lives in sub-Saharan Africa.

There are only about 10,000 left in the wild, doing their best to outrun extinction.

And here in Namibia, they appear to be winning the race of their lives.

A key stronghold for the cheetah is Etosha National Park, in Namibia's north.

The landscape here is unbelievably harsh, but nonetheless, it helps Namibia lay claim to the title cheetah capital of the world.

In the center of Etosha, there's an ancient salt pan which, during the rainy season, draws four-legged and two-legged visitors like a magnet.

Including many of the nation's cheetahs.

With a top speed of 100 kilometers per hour, cheetahs can outrun any animal on Earth.

But the first stage of any hunt begins with stalking.

Cheetahs have keen eyesight and excellent camouflage, so they aim to get as close to the prey as possible without being seen.

Then, the pursuit begins.

Accelerating faster than a sports car, it takes just three seconds for a cheetah to reach its top speed.

And when it does, it's virtually flying.

Their long tails act like rudders, allowing the animals to make sudden changes in direction, and their claws do not retract when they run.

Rather, they act like running spikes when their feet hit the hard ground.

Cheetah hunts result in a successful kill over 50% of the time, a much better success rate than leopards or lions.

Cheetahs are smaller than the other big cats, so they prey on comparatively small animals-- gazelles, hares, and the young calves of wildebeest.

Outside the mating season, cheetahs are solitary animals.

Females look after their cubs alone, spending two years providing for them, playing with them, and teaching them all they need to know about surviving in the grasslands of Africa.

Camouflage is a fundamental necessity for many animals trying to stay out of harm's way on Africa's savannahs.

But one gentle giant with very little chance of ever staying out of sight and off the safari radar is the giraffe--the tallest animal in the world.

A full-grown bull can be five and a half meters tall.

The fact that giraffes can reach into the boughs of large acacia trees means they are able to live amicably alongside other herbivores, for there's no need to compete for food.

When it comes to eating, giraffes are uniquely equipped.

First, there's that unbelievable tongue, up to 45 centimeters long and amazingly agile, enabling the giraffe to pluck out the most tender shoots.

Giraffe tongues need to be tough as well, for Africa's acacias are covered in thorns.

Giraffes have seven vertebrae in their necks, just like humans and, indeed, most other mammals.

But theirs are linked together with ball and socket joints, which give them a great deal more flexibility.

The joint between the neck and skull allows a giraffe to extend its head at an almost 90 degree angle to the ground.

Male giraffes participate in a ritualized fight called necking.

Their reinforced skulls can normally take the impact of these blows, but giraffes do occasionally knock themselves unconscious during these fights.

The horn-like nobbles on the giraffe's head are known as ossicones.

They are not true horns but hardened cartilage covered in skin and sometimes a small tuft of hair.

Both sexes have them from birth, although they lie flat for the first few months of life.

Up until recently, zoologists believed there were only two species of giraffe in Africa, but recent DNA tests have pointed to at least five different species, each living in a geographically distinct area of the continent.

Just like human fingerprints, each giraffe has a unique pattern, so scientists can easily identify individuals.

Giraffes are already exceptionally tall at birth.

Most babies are over two meters, so they can immediately reach to suckle their mothers.

Giraffes play a significant role in maintaining the health of the grassland trees.

Their browsing technique encourages fresh plant growth and they distribute seeds far and wide via their dung.

In dry places like the Kenyan Savannah, giraffes also need to drink a lot of water, not the easiest maneuver to effect when you have such a long neck and spindly legs.

Any lesser animal would surely faint.

Fortunately, the giraffes' blood pressure is twice as high as humans', and their hefty, hard-working hearts beat almost twice as fast, so they have the means to prevent themselves from passing out when they move their heads from down low to up high and vice versa.

With all that pressure pushing down on their splayed legs, it's a wonder the blood vessels in them don't explode.

But giraffes' limbs are wrapped in tough membranes which compress their veins and arteries in much the same way as a G-suit works for a fighter pilot.

In fact, scientists from NASA have studied this particular aspect of a giraffe's physiology and used their findings to perfect the design of their astronauts' space suits.

It's quite remarkable to think that this gentle grassland animal is now contributing to exploration beyond the bounds of the planet we share, perhaps enabling humans of the future to have close encounters of a very different kind.

There's really no denying the fact that parts of Australia look like Mars and that many animals living on this continent could pass themselves off as aliens.

But two of the nation's most abundant grassland animals are indisputably Australian and recognized as such the world over.

Indeed, they even take pride of place on the country's coat of arms.

The kangaroo and the emu.

The emu, with its long legs and long neck, is Australia's tallest native bird.

They can reach nearly two meters in height when standing erect.

They can't fly, but can run at speeds of 50 kilometers an hour.

Emus are good sprinters but they're also built for endurance.

They can roam huge distances in search of food, sometimes covering 25 kilometers in a day.

Food supplies in the Australian outback can be unpredictable at best, so the ability to move to other distant feeding grounds is essential for survival.

The parenting patterns of the emu are also quite unusual.

Male and female pairs remain together for the first five months of their breeding cycle.

But the male will then take full responsibility for hatching and caring for their young.

Kangaroo joeys are raised entirely by their mothers.

There are nearly 70 different species of kangaroo in Australia, filling every niche on the continent.

But most are built for the wide open spaces of the outback, Australia's version of the globe's great grasslands.

Like most Australian mammals, kangaroos are marsupials.

They're known among scientists as macropods, meaning large feet, and as a group include wallabies, pademelons, and bettongs.

They come in an incredible variety of shapes and sizes, from the rabbit-sized pottaroo to the man-sized big red.

They all have strong, oversized hind legs and tails and the ability to bound at high speed using long, graceful leaps.

Some species are extremely rare and restricted to small areas, but the most commonly seen kangaroo is the Eastern Grey.

These soft-featured animals can be found along the eastern third of Australia, between the coast and the inland deserts.

Like many kangaroos, Eastern Greys are social animals, living in groups known as mobs.

Each mob is dominated by an alpha male with several adult females and their joeys at various stages of development.

Female kangaroos can be looking after three joeys at once.

The oldest will have just left the pouch and be learning to fend for itself, nibbling on young shoots but staying close to its mother.

A younger joey will still be developing inside the pouch and a third will be in the embryonic stage of its development, in a state of suspended growth scientists call diapause.

As soon as the middle joey is old enough to leave the pouch, a chemical signal triggers the embryo to grow.

Eastern Greys are mainly nocturnal, preferring to rest during the heat of the day and coming out to graze at dusk.

Many Australians believe the kangaroo and emu feature on the nation's emblem because neither animal can walk backwards, symbolizing the country's highest aspirations, always moving in a forward direction.

There are actually quite a few countries that feature grassland animals in their state emblems, but South Africa's is something of a standout.

In a country bursting at the seams with regal options, such as lions, leopards, and elephants, South Africa has chosen the enigmatic secretary bird to crown its National Coat of Arms.

Supposedly, the secretary bird was so named because it bore a striking resemblance to the male secretaries of the 1800s, with goose-quill pens tucked behind their ears, grey tail-coats, and dark knee-length pants.

Preferring to walk rather than fly, this large bird of prey can cover 30 kilometers in a day searching for food.

They are well known for their ability to catch and kill snakes, but will also eat small mammals, reptiles, and large insects.

Dispatching of prey either involves a swift strike with the bill, or a not-so-soft shoe shuffle, stomping on a potential meal to either knock it unconscious or kill it.

Secretary birds are widespread throughout Africa, south of the Sahara, and a key species on every birdwatcher's wish list.

They're easily encountered in Sabi Sands, a game reserve that borders Kruger, one of the largest national parks in the world.

There are no fences between the two parks, so all the animals are free to range between the two.

White rhino, elephants, hippo, lions, and the world's largest bird: the ostrich.

Another remarkable animal here that's native to the southeastern region of Africa is the nyala.

The nyalas' preferred habitat is in areas where the savannah and woodlands merge.

They're a handsome species of antelope, so males will hang onto those large horns for life, using them, as male antelopes so often do, to advertise their genetic superiority and fight with other males for the right to mate.

A far easier antelope to encounter in the Sabi Sands savannah is the impala.

They are often seen in large herds, which offer a measure of protection from predators, such as lions.

When danger approaches, the first impala to notice will sound the alarm with a loud bark, sending the whole herd into flight.

Impalas are not only very fast runners, they're agile and strong, and can leap into the air as they run.

Another unusual move they affect is called stotting or pronking, which in Afrikaans means showing off.

This sublime landscape of deep forests and subtropical grasslands has undergone a miraculous transformation.

It used to be the royal hunting ground for Nepal's rulers and their guests.

Big game here included the Bengal Tiger, the Gharial Crocodile, and the largest rhino species on the planet, the Greater One-Horned Rhino.

These huge rhinoceros once roamed the entire northern part of the Indian subcontinent, but by 1975 they were facing extinction.

Only 600 remained in the wild.

Conservation efforts since then have turned the Greater One-Horned Rhino's fortunes around, increasing their numbers more than six-fold, with Chitwan boasting the second largest population of this species in the world.

Chitwan is now a World Heritage Site and with three decades of successful wildlife management under its belt, the place is positively booming.

Elephants, rather than safari jeeps, are used here for transport, carrying those who seek to encounter these amazing animals at close range.

The Greater One-Horned Rhino has a single black horn, which can grow to over half a meter in length.

It also has distinctive folds in its skin which give the impression of armor plating.

The skin of a Greater One-Horned Rhino can be up to four centimeters thick.

Add another two to five centimeters of subcutaneous fat and you are looking at one very thick-skinned animal.

All that fat seems strange for a mammal living in a hot climate, but it is well supplied with blood, which helps the rhino to regulate its body temperature.

One-horned rhinos feed on a wide variety of plants; grasses, fruit, leaves, and branches are all on the menu.

Most of these rhinos live a solitary life when they're not mating or breeding.

Each male has a defined territory, which changes with the seasons and according to food availability.

But he will fight to the death to defend it.

Although they're short sighted, these rhinos have an excellent sense of smell and good hearing.

They communicate using at least 12 different sounds including snorts, honks, and roars.

Sighting just one individual of a species that has so successfully bounced back from the brink is exhilarating.

But many would argue that quantity trumps quality when it comes to animal encounters.

And on that front, the Serengeti doesn't disappoint.

During May and June, when the annual migration is in full swing, the Serengeti is awash with wildlife.

This event is widely regarded as the greatest wildlife spectacle on Earth.

Great waves of zebra, wildebeest, and gazelle are on the hoof, moving north from their grazing lands in Tanzania to Kenya.

The monsoon in the south is long over and the grasslands will soon dry out.

The escarpments up north in the Maasai Mara are catching the last of the rains, so this is where the grazing animals must head.

Around two million animals move through the Serengeti, marching towards greener pastures.

Most of them are wildebeest.

Wildebeest are the major food source for many of the predators of the African grasslands.

But by gathering in enormous herds and following the food, these stoic animals can keep their numbers high.

Hundreds of thousands of zebra also join the pilgrimage.

Those charismatic stripes do a whole range of things to keep the zebra functioning happily.

They break up the outline of each zebra's body so predators cannot spot them in the long grass.

As a herd, they create a mesmerizing pattern, so it's almost impossible for hunting lions or hyenas to target an individual.

Scientists now believe the stripes serve a third function.

These open plains can reach temperatures of 30 degrees Celsius and there's little shade from the equatorial sun.

The alternating black and white stripes absorb heat at different rates.

This probably sets up a microclimate of air currents on each zebra which keeps the animal cool.

As the migration progresses, the most dangerous challenge of the journey comes closer.

The crossing of the Mara River.

The steep, unstable river banks and deep and fast-flowing water are difficult enough.

But that is just the beginning.

Many hungry carnivores are lying in wait.

The banks of the river hide hungry leopards and lions on the lookout for stragglers.

They know the river crossing will be too much for some.

But the greatest danger of all lies just below the surface of the muddy waters-- Nile crocodiles.

Enormous, strong, and startlingly fast.

But the hungry herds are driven by the promise of fresh grazing on the other side of the river.

They have no choice but to take their chances.

This is survival of the fittest at its most brutal.

Getting across the Mara alive is a numbers game.

Of the thousands of animals crossing, less than 1% will be killed.

But there's still one more obstacle before safety is reached.

At many crossing points, the banks of the Mara can be high, steep, and unstable.

Getting out of the river is as dangerous as getting across it.

In 2007, 10,000 wildebeest drowned when the far bank was just too steep to climb.

Once clear of the river, the animals are in the Maasai Mara Reserve.

There's plenty of grazing and time to recover before making the return journey in six months' time.

This great migration is one of the ultimate wildlife experiences in the world, and with luck on your side, you'll have a front-row seat to a truly breathtaking animal encounter.

From the prairies of North America... to outback Australia and beyond... grasslands offer a wealth of opportunity to get up close to the world's greatest herbivores... and the predators that relentlessly pursue them.

To witness the drama playing out in these theaters of life is a privilege indeed... and a reminder of just how fortunate we are to share our planet with a cast of thousands.

(triumphant music)