Narrator: High in the mountains, deep underground; in deserts and frozen wastelands, life is no bed of roses.

These animals certainly drew the short paw when habitats were being handed around.

Scorching heat, numbing cold, total darkness, and dangerously thin air.

These are just some of the challenges faced by animals living in extreme environments.

Superbly adapted to these inhospitable habitats, their fortitude and resilience is astounding... From the top to the bottom of the world.

Close encounters with stoic creatures such as these, leave us, literally, gasping in awe.

[horses nicker] The arctic circle is a truly remarkable place.

It encompasses parts of the U.S., Russia, Finland, Sweden, Iceland, Greenland, and Norway.

But the ocean is its most significant feature-- roughly 14 million square kilometers of ice-laden sea.

Winter temperatures here can drop below minus 50 degrees celsius, and the wind can whip itself into a frenzy, double the speed of a hurricane.

Weighing in at around 680 kilos, the top predator in this extreme landscape is the polar bear.

They are renowned for keeping to themselves, but in some places, polar bears and people have developed a mutually dependent relationship.

Just on the outskirts of the town of Churchill in Canada, polar bears come to scavenge for food.

Locals have taken advantage of their presence and made it possible for animal lovers to have a close and yet safe, encounter with this polar powerhouse.

Polar bears are perfectly put together for a life on ice.

They have a layer of fat, or blubber, that insulates their bodies from the bitterly cold air and water.

That thick coat of fur extends to the soles of their feet, keeping out the cold and aiding traction.

Each hair is translucent, but the polar bear's pelt appears to be white because it reflects light.

It's great for camouflage but beneath all that fur, the polar bear's skin is black, allowing the animal to more effectively absorb heat from the sun.

Polar bears are powerful swimmers.

One bear fitted with a tracking device was recorded swimming continuously for over 9 days, and in that time covered nearly 700 kilometers.

Scientists studying polar bears have figured out a way to isolate their DNA and that of their last meal, from the footprints they leave in the snow.

Polar bears spend around half their lives hunting, but before they're old enough to fend for themselves, male cubs appear to spend a great deal of time play-wrestling.

Most polar bears are twins, so most have a playmate from birth.

Through this instinctive behavior, they learn important skills they will need later in life, when the time comes to compete with other males for the right to mate with the females.

These fights can be aggressive, lasting several hours and invariably leave both challengers scarred for life.

As adults, polar bears are generally solitary creatures, but as cubs, they tend to stick together, even after they've left their mother's side, mock fighting and hunting until it's time to go their separate ways.

The polar bear is the largest of all the arctic animals on land.

Second in line is the musk ox, a huge bovine beast that is relatively easy to encounter on the arctic tundra.

They are well-adapted to withstanding the bitterly cold winds and temperature, with strong hooves to dig through the snow for food and not one, but two coats to keep them warm through the winter.

Their diet is strictly vegetarian--mosses, roots, and lichens through the winter, arctic flowers and grasses during summer.

Iceland is widely known as the land of ice and fire.

It is an extremely remote, yet inhabited part of the arctic that harbors huge glaciers and active volcanoes in equal measure.

There are crystal-clear rivers... barren highlands... soaring fiords... and along the coastline, precipitous cliffs that provide an extreme home base for two of the arctic's most interesting birds-- the rather comical-looking puffin and its key predator, the skua.

Skuas can snatch puffins mid-flight, but they are much easier to catch when they're stationary.

[squawks] Puffins spend most of their time at sea, resting on the waves when they're not flying or diving to catch fish.

But when it's time to breed, they need to find land.

Cape Ingolfshofdi, an isolated headland on the South Coast of Iceland, is a favorite nesting site, protected by a nature reserve, where bird enthusiasts are able to encounter puffins at close range.

Males dig burrows into the cliffside with their beaks.

Both parents take turns to incubate the single egg the female lays and will share the care of their offspring once it hatches.

Easily identified by their colorful beaks, puffins are often referred to as "sea parrots."

And despite their relatively small wings, they are impressive in the air.

Flapping their wings 400 times a minute, they can reach speeds up to 88 kilometers per hour.

Most seabirds can only catch one fish at a time, but puffins have lots of small spines on their upper palates that allow them to hold onto as many as a dozen-- an efficient strategy when parents need to bring food back to their nests to feed their pufflings.

Remarkably, every year the same couples return to nest in the same location.

scientists are still not certain how they manage to find their home grounds so precisely, but some suggest they may be using the earth's magnetic field or even stars to navigate.

The night sky in the arctic is certainly a wonder to behold, especially when atmospheric conditions conspire to produce one of the most extraordinary natural phenomena on earth--the aurora borealis, or northern lights.

The science behind this awe-inspiring display can be simply explained.

This is what happens when gaseous particles in the earth's atmosphere collide with charged particles emitted by the sun.

This celestial ballet that ignites the polar skies ignites our sense of wonder, too, leaving many transfixed by its haunting beauty.

On the other side of the arctic circle, long before europeans arrived in North America, wild dogs roamed through this vast wilderness untethered.

To this day, they form the genetic base for the modern alaskan husky, the tireless sled dogs of the great north.

They are a domestic animal, but so integral to human survival in this part of the world, it would be remiss not to include them in the world's greatest.

Alaskan huskies were developed by dog sled racers, or mushers, from different bloodlines of native Inuit dogs.

They love to run and they love to haul-- two sought-after traits that generations of breeding have perfected.

[barking] [dripping] The ultimate challenge for the dogs and their mushers is the Iditarod, a grueling 1,500-kilometer race from anchorage to nome.

Each competing team has between 12 and 16 dogs, that are rotated throughout the course to prevent fatigue.

Vets give the competing dogs the once-over at each and every checkpoint, to ensure they are up for the challenge.

The dogs are well cared for by their mushers, and seeing the relationships they've developed with their masters is heartening.

[barking] Dog-sledding is not only a great way to connect to these beautiful animals, it's also a practical way to get around the wilds of Alaska-- clearly, a part of the U.S.

blessed by mother nature.

At the opposite end of the extreme landscape spectrum, where the Pacific and Indian Oceans converge, bitter cold is traded for relentless heat and humidity.

This is a landscape born of fire.

home to more than 120 active volcanoes, the Indonesian archipelago is almost constantly threatened by earthquakes and tsunamis.

Eruptions can be catastrophic, but they lay the foundations for new life to take hold.

Beneath the sea, where the world is perpetually dark, hydrothermal vents provide an extreme habitat for a strange array of creatures... shrimp and fish that appear to thrive on the mineral-rich hot water escaping from deep inside the earth.

Other animals living in the extreme ocean depths here, include crabs... holothurians... and the world's deepest living super predator, the bathysaurus, or lizardfish.

in this dark and lonely world, it has evolved an unusual reproductive mechanism--the ability to copulate with any member of its own species, for all are equipped with both male and female sex organs.

A land-based animal here in Indonesia, with an equally unusual way to reproduce, is the Komodo dragon.

Their hostile habitat means that individual dragons are extremely isolated, so lone females have evolved the ability to reproduce asexually.

Komodo dragons are the heaviest monitor lizards in the world and they've been around for at least 4 million years.

Fossils suggest they originally came from Australia and moved westward when sea levels were low.

Fully grown adults can be 3 meters long and weigh over 150 kilos.

They use that forked tongue just like a snake, to taste the promise of prey in the air.

Dragons will often lie in wait for their prey.

they have excellent camouflage and a great deal of patience, but powered by their massive, muscular tails and legs, they can launch an attack with surprising speed.

Sharp claws and teeth make short work of prey.

If by some miracle, a dragon's intended meal escapes, it won't be for long.

For the lower jaw of this incredible killing machine is packed with lethal venom, that finds its way into the dragon's saliva and its victim's bloodstream.

these animals are extreme eaters.

One dragon can eat 80% of its body weight in a single sitting.

its jaws and throat can stretch to accommodate enormous chunks of food.

[flies buzzing] Almost nothing goes to waste.

bones, hides, and even hooves will disappear down that massive throat.

of the 69 species of monitor lizards in the world, Australia is home to 28. the perentie is the island continent's largest, second only in size to the Komodo dragon.

They're 2.5 meters long, impressively fast, and show remarkable endurance.

They can run on their hind legs and reach speeds of 40 kilometers per hour.

They live close to rocky hills and outcrops, using those saber-like claws to dig burrows in the hard earth.

perenties and their close relatives, the Rosenberg's goanna, do not lay their eggs in their burrows.

They prefer to take advantage of these perfect incubation chambers... built by termites.

the vents and tunnels termites create to keep the temperature and humidity of their homes constant provide the perfect conditions for perentie eggs to incubate.

An added bonus, when the young hatch, there's a quick meal available on the doorstep.

As adults, these enormous monitor lizards have an extreme diet, for they specialize in catching and eating venomous snakes.

When the situation calls for a showdown, perenties can outpace and outsmart a king brown, one of the deadliest snakes in Australia.

Another extreme Australian animal with a deadly diet, is the portia spider.

It preys on other spiders, including the poisonous red-back, a close relative of the notorious black widow spider in the U.S.

Despite its diminutive stature, the portia spider is a ruthless assassin, readily taking down prey larger than itself.

stealth is the name of the game in this extreme arachnid's world.

And if it takes hours, or even days to sneak up on a potential meal, so be it.

The portia spider is said to be the most intelligent spider on the planet, deliberately stalking and even plotting how best to effect a kill.

And if that method doesn't work, it will cleverly switch to a different strategy.

In another hot, dry landscape thousands of kilometers away, there are yet more animals appearing to defy the odds living in hostile terrain.

The Namib desert park in Namibia, near the southwestern tip of Africa, occupies an area larger than Switzerland.

and while it lacks the high mountains that define the topography of that particular nation, it is home to some of the world's highest sand dunes.

the tiny grains of sand that make up the dunes in the center of the world's oldest desert, are said to be over 5 million years old.

For all its apparent hostility, this otherworldly landscape, surrounding the Sossusvlei salt and clay pan, provides an unlikely habitat for some truly resilient animals, including ostrich and the superbly adapted gemsbok, or oryx.

While they will drink water if the opportunity presents itself... they do not depend on it to survive.

They can go for months on end without it.

The roots and tubers and wild melons they eat when grass is sparse provide all the water they require.

Their physiology and behavior is geared to minimize the loss of body moisture.

They do not urinate very often, and when they do, the flow is as thick as honey.

And as counterintuitive as it sounds, they stop sweating when desert temperatures soar.

in any lesser animal, this would be lethal, but the gemsbok copes with its body temperature rising to a dangerous level by panting rapidly, cooling the blood in its nasal veins before it reaches its brain.

Gemsbok live in herds of between 10 and 40 animals.

and in Namibia, their population is thought to be around 373,000. in other arid parts of South Africa, they are hunted for their spectacular horns.

But here in the Namib desert park, the only humans seeking to fix them in their sights are photographers.

[thunder] Extreme weather is almost par for the course in Australia.

Heat waves, cold snaps, dry spells and floods ravage the landscape.

In the desert, the temperature regularly soars over 48 degrees celsius.

And in the alps, in the dead of winter, it can drop to a numbing minus 8.

But one animal thriving in both environments is the wild horse, or brumby.

They are relatively recent arrivals in Australia, but nonetheless, have become integral to the nation's cultural identity.

They descend from horses that were shipped in with the first European colonists and cart horses used during the gold rush.

their ancestors were ridden by bushrangers and troopers, by stockmen, explorers, and pioneers.

There is even one wild herd of brumbies whose forebears carried soldiers gallantly through both world wars.

Numbering close to a million, these majestic steeds provide an enduring, tangible link to the nation's wild colonial past.

For 150 years, these brumbies have been roaming free in the high country, alternately surviving the vagaries of summer bushfires and winter's bitter blizzards.

They hold their own in arid Australia, too.

[horse nickers] But the prize for enduring all that harsh environment has to offer goes to another non-native animal--the camel.

Camels were introduced here in the 1840s From India, Arabia, and Afghanistan, to assist the colonists in their exploration of Australia's inland.

But when motorized transport found its way into the outback and the camels were no longer needed, thousands were released into the wild.

[camels grunting] With no natural predators, they flourished.

They now form the largest herd of camels on earth, with their numbers nudging a million.

The dromedary, or one-humped camel, is native to the Middle East And horn of Africa, where it's been domesticated for 3,500 years.

[grunting] Bedouin tribes have traditionally used camels for transport and trade.

The camel's ability to travel hundreds of kilometers without water is well-documented.

Unlike most 4-legged animals, they move both legs on one side of their body at the same time, giving their gait a rolling motion, not dissimilar to that of a boat, which is one reason why they're often referred to as the "ships of the desert."

Big, thick footpads help them withstand the hot, shifting sands or rocky terrain typical in most of the world's desert regions.

They have a third, transparent eyelid and two rows of eyelashes to protect their eyes and can close their nostrils to stop sand from getting in, when the wind is whipping it into a frenzy.

Their lips are big and tough and impervious to the prickly vegetation that typically grows in a desert.

And they don't need to sweat until their body temperature reaches 41 degrees celsius, effectively conserving any fluids they consume for long periods of time.

When they do drink, they do so with gusto, soaking up water like a sponge... downing 135 liters in 13 minutes flat.

contrary to an age-old belief, camels do not store water in their humps.

They're reservoirs of fatty tissue, a source of water and energy when these resources are scarce.

As that fat depletes, a camel's hump can become quite floppy, a sure sign it's losing condition.

[camel grunts] Most animals living in the snow, have a tough time during winter, enduring snowstorms and a ccarcity of nutritious food.

but the Japanese macaques on the Shimokita Peninsula on the island of Honshu, have learnt how to ride out the winter in relative comfort.

It's a clear case of monkey-see, monkey-do, for the ancestors of these macaques are thought to have mimicked human behavior, in taking to the hot springs for a measure of respite from the chills of winter.

The pool rules seem to vary from day to day and from group to group.

Sometimes you'll see a sedate gathering of monkeys calmly taking to the water, like wise, old monks.

And at other times, well, it's all a little less ordered and serene.

Japanese macaques need to have a broad taste in food in order to survive here.

They will eat almost anything they can find, including over 200 different fruits and seeds, insects, and even sometimes soil.

But it's their taste in bathing activities that sets them apart from all the other extreme animals on earth.

Animals can survive in all manner of extreme environments-- in intense heat, in severe cold, and in complete darkness.

caves all over the planet harbor creatures that have evolved to survive in a lightless world.

Longfin eels rely on their sense of smell to find food.

And bats find their way in and out of their cavernous daytime roosts using echolocation.

It's a tough call choosing the world's most extreme animal taking advantage of the protection such subterranean habitats afford.

But as far as encounters go, few hold a candle to the glowworm.

These bizarre lifeforms only exist in the southern hemisphere.

And one of the most amazing places to witness them in all their glory, is Waitomo caves in the North Island of New Zealand.

The ways into this exquisite cave system are adventures in themselves-- floating through some of the larger caverns on an inflated car tire inner tube or employing the more traditional techniques used by professional cavers.

either way, the glowworm displays are worth the effort.

When millions of these animals get together, the result is truly out of this world-- an ethereal galaxy of glowworms.

Glowworms are not actually worms.

Rather, they are maggots, the larval stage of a small fly.

The larvae live like this for about 6 to 9 months before transforming into adults that, lacking mouths and stomachs, will only live for 3 days.

Their sole purpose as adults is to reproduce before they die.

The life of a young glowworm however, is all about eating, and this is one big, cooperative trap.

Each light is a single larva.

A chemical reaction in the larva's feces causes the bioluminescence.

The skin of the larva is translucent, so the light shines through from inside the animal's intestine.

Thousands of lights together attract thousands of insects, such as these cave-dwelling moths.

Each glowworm dangles a long sticky thread that acts like a fishing line.

When insects are drawn to the lights, they become entangled and trapped.

It's bad news for the bugs, but manna from heaven for the glowworm.

Outback Australia is a harsh and unforgiving environment... full of small creatures that have adapted well to its alien vagaries.

To the spikey spinifex and endless gibber plains that don't exactly give off a very welcoming vibe.

it's the driest inhabited continent in the world, with 2/3 of the mainland classified as arid or semi-arid.

and much of it is prime habitat for the beady-eyed and scaly skinned.

Australia harbors more reptiles than any other country on earth, over 900 native species, including many of the world's deadliest snakes.

This is the inland taipan, the most potent snake in the world.

If it were to strike a rat, it would inject a venom 40,000 times more lethal than necessary.

The ultimate overkill.

The prey dies very quickly with little resistance, so the risk of injury to the taipan is minimized.

The taipan can live where almost no other animals can, hiding in cracks and crevices.

They can survive with no plant cover whatsoever, and they have a clever desert adaptation.

They change color according to the season, from a light-cream to reflect heat during a summer to a dark-brown for absorbing heat in the winter.

the largest of all of Australia's venomous snakes is the mulga snake, or king brown.

King browns compete successfully with other desert snakes by choosing a different food source.

While most snakes prey on small mammals, king browns specialize in eating other reptiles-- snakes, lizards, and even their own flesh and blood.

When attacking, they bite down hard, chewing to inject more and more venom.

The king brown wins the international prize for having the highest venom output of any snake in the world.

While most snakes will escape rather than risk an attack, there's one species that prefers to sit motionless wWhen it hears someone coming... the death adder.

Like all snakes, they're not interested in us as prey, but unwary bushwalkers may get bitten by accidentally standing on one.

These snakes have the longest fangs in the world.

They are ambush predators, so their camouflage is excellent.

Death adders are easy to identify.

They are short and squat with striking markings and a triangular head.

The end of their tail tapers quickly and is a different color, which the death adder uses as a lure.

Mimicking the movement of a worm, the adder attracts prey by wriggling its tail until curiosity draws potential prey close enough to strike.

Despite its appearance, this is also the fastest snake in Australia.

One of the most fearsome- looking, yet harmless reptiles in the Australian desert is the thorny devil.

It is small, but extreme, particularly when it comes to what it eats and how it drinks.

Thorny devils are only around 20 centimeters long, and they dine exclusively on ants.

Their thorny skin is a deterrent to many potential predators, but more incredibly helps a devil to drink.

They can stand in a puddle of water and channel the liquid uphill into their mouths via the grooves between their scales.

This clever gravity-defying adaptation allows thorny devils to rehydrate without taking their eyes off the skies, where aerial predators are hunting for a meal.

Another tactic they use to avoid being eaten is to look like a leaf, rocking back and forth as if it were blowing in the breeze.

The thorny devil also has a bony mass or false head on top of its real one.

If threatened, the devil tucks its real head between its legs, so the fake head is exposed, making the lizard look bigger and thus more difficult to swallow.

In doing so, the clever thorny devil has the chance to live another day in this extremely hostile environment, keeping ant populations in check.

When it comes to aerial predation, the Andean condor is in a league of its own.

Nearly twice as deep as the Grand Canyon, Colca is in the heart of the Andes, in Peru.

Waters cascading down the mountains have carved this incredible chasm in the earth.

It is an extreme environment, and the domain of one truly remarkable vulture.

Andean condors have a wingspan that can reach 3 meters from tip to tip.

With a top weight of over 15 kilos, this is the largest flying bird in the world.

Despite their heavy bodies, condors seem to fly almost without effort, barely flapping their wings.

Each bird is being carried by the strong air currents generated by the deep canyon and surrounding rocks.

Condors are gliders rather than fliers.

They are expert at finding rising columns of air to carry them through the mountains.

Tiny movements of their primary feathers adjust the condor's climb and direction.

Condors have excellent eyesight, ever on the lookout for signs of a meal.

They're not well-equipped to do their own killing, for they lack the lethal talons of eagles and hawks that can bring down prey in a split-second.

Instead, they must scavenge for animals that are already dead.

Condors are very clean animals.

They're often preening their feathers.

And that bald head has evolved so they can dig deep into carcasses without getting covered in rotting meat.

the steep sides of Colca Canyon are ideal nesting sites and perfect launch pads for these extremely oversized birds.

Despite their grace in the air, condors find it very hard to take off from the ground.

So this terrain that seems so inhospitable to us is the perfect home for this truly awe-inspiring bird.

The Southern Ocean surrounds the driest continent on the planet.

It's also the windiest.

Dense, freezing air rolls down the mountains at speeds of over 300 kilometers an hour.

Antarctica is a place of immense beauty and mystery that's almost completely blanketed in permanent ice.

And some of this ice is almost 2 miles thick.

And, of course, it's extraordinarily cold.

The lowest temperature ever recorded on earth, was minus 89.2 degrees, at Vostok in the Australian Antarctic territory.

Even without the ice, the continent of Antarctica is big-- much larger than Australia, tith mountains over 5,000 meters high.

Very few animals can survive here.

To do so, they have had to evolve some extremely specialized physiologies and behaviors.

Seals, whales, and penguins all have personal insulation in the form of thick fat layers known as blubber.

The supreme example of Antarctic adaptation is a flightless bird weighing 40 kilos-- the regal-looking emperor penguin.

This is the only land animal on earth that breeds during the antarctic winter.

It has special nasal chambers that recover heat lost through breathing, and even its blood vessels recycle heat by aligning themselves close together.

But the most amazing feature of this stoic bird is its wonderful social behavior.

Emperor penguins are famous for their enormous huddles, sometimes as big as 200,000 individuals.

Amazingly, the temperature close to the center of these groups can be a balmy 24 degrees celsius.

Fortunately for the penguins on the outside, the entire group is constantly moving.

In this way, every penguin enduring the icy winds will eventually cycle into the middle.

This behavior is made all the more remarkable by the fact that each animal is balancing an egg on its feet.

If the eggs make prolonged contact with the ice, the chick inside will freeze to death.

Another species of penguin living on the fringes of Antarctica in super colonies, is the gregarious chinstrap penguin.

There are around 4 million breeding pairs in Antarctica.

They are the athletes of the penguin world, capable of climbing with all 4 limbs and jumping large distances.

Gentoo penguins prefer to breed on subantarctic islands so are often seen much further north.

These little birds will fiercely defend their nests against predators and other penguins.

There are 6 species of seal living in these waters, and all of them are large carnivores.

The most feared is designed for underwater speed and has lethally long canine teeth-- the leopard seal.

These animals are huge, with females reaching 3.5 meters in length and weighing 500 kilos.

Leopard seals live and travel alone.

they eat penguins and other seals as well as fish and squid, and they've been known to hunt humans.

Apart from the lethal cold, the leopard seal is the greatest danger to people living or traveling through Antarctica.

The Weddell seal is almost the same size as the leopard, but it has a small head, small mouth, and a placid nature.

The biggest and most well-known colonies of seals down here are either elephant seals or Antarctic fur seals.

Both societies consist of a harem of females and one very aggressive dominant male.

Unlike northern hemisphere seals, all Antarctic species have no natural predators on land and appear as curious about us as we are of them.

Extreme animals often live in extreme environments... places that appear to be anything but conducive to life.

Many of their behaviors and adaptations defy belief... and the way they cope with living life on the edge inspires our respect and sense of wonder.

[horses nicker] Whether they live at the top or the bottom of the world or somewhere in between those geographic extremes, they have clearly earned their place among the greatest animals readily encountered in the world.