Meadows that only a few weeks ago were buried beneath the snow are now full of life.
But in these mountains, the good times will not last long.
So the bears must feed as fast as they can.
During the summer months, an adult can put on 180 kilos, gorging on plants.
And if they can catch them...
A marmot or two.
But just now, the bears have something else on their minds.
It's becoming warmer, and the bears are keen to shed their thick winter coats.
Mothers show the cubs what to do about this.
They'll soon catch on.
Some trees, it seems, are particularly suitable for rubbing.
Bears have their favorites and will travel long distances to visit them.
Some itches just have to be scratched.
There are now around 30 bears in this one valley.
As they rub, each leaves an individual and recognizable scent.
So the tree soon carries a list of who's around, which might help individuals to avoid a fight.
To best spread their scent, they really have to put their back into it.
But summer is short.
Itch is satisfactorily scratched.
It's time to eat.
In a couple of months, they will have to return to their dens to hibernate.
So now they must put on as much weight as they can.
With little to eat down here.
Many of Borneo's terrestrial mammals are smaller than on mainland Asia.
Confined to her protected forest sanctuary, the exceedingly rare Bornean sun bear.
Just over a meter long, it's the smallest bear in the world.
Fallen branch is a valuable treat.
Filled with wood grubs and beetles, nothing is wasted.
Even a foul-tasting millipede.
But it's not enough to sustain even this little bear.
The real prize sits high above.
Guided by her exceptional sense of smell, it's the sweet scent of honey.
For larger bears, this beehive may be out of reach.
But being small helps defy gravity.
With sharp claws and rough pads on her feet.
She can ascend 40 meters higher than any other bear to make it in Borneo's jungle treetops.
This miniature acrobat has become more monkey than bear. suitable for her cubs.
This is their first ever trip to the seaside.
In a few hours, the tide will return.
So they must keep up with mum.
Here's something tasty.
Crabs.
Big crabs can give a nasty nip. so it's best to start off with smaller ones.
During spring, three quarters of the bear's food comes from the beach.
But now this family is not alone.
An adult male.
He's double her size, and they're in his territory.
The cubs know that call.
It's time to head for safety.
Bears have poor eyesight, but their sense of smell is acute, and the male has detected intruders.
He knows exactly which tree they are in.
If the cubs stay up there, they'll be safe, but they're losing precious feeding time.
For now, he's content to leave his scent mark. a warning note for trespassers.
The family moves on.
For the cubs, lunch today will have to be a takeaway.
The tide comes in.
And within minutes, feeding time is over for another day.
The bear must regain his strength.
The next day, a sea fog shrouds the island.
The wallaces sense that they're in danger.
Using the fog as cover, the bear approaches the herd.
The adults close ranks around their young, presenting a wall of blubber and hide.
He tests the banner.
But it stands firm.
It appears that the world's largest land carnivore has met his match.
There must be a chink in the armor somewhere.
Not here.
This female walrus is shielding her pup if he can just prise her off.
The bear's claws and teeth can't penetrate her thick hide.
With the herd retreating to water, the bear must move quickly.
Having failed with one, he heads straight for another.
The chance of his first meal in months is slipping away.
He seems increasingly desperate.
It's now or never.
He must avoid the stabbing tusks if he's to win.
The flailing walrus is immensely powerful and drags the bear away from the shallows towards the safety of the herd.
It slips from his grasp.
Forest once covered 80% of Europe.
Now, only half of it remains.
One of only 1,500 that are left in Finland's forests.
Her cubs have recently emerged from their nursery den.
The long summer days means there's plenty of time for play.
With two boisterous cubs, it pays to rest whenever you can.
But their mother must be on her guard.
The cubs have spotted something.
A large male looking for a mate.
The cubs aren't his. so he might try to kill them.
Their cubs are excellent climbers.
And now they're beyond his reach, 15 meters up.
Their mother warns him to keep his distance.
But the cubs are coming down too soon.
She can't take any chances.
That was a close call.
Finland's forests give us a glimpse of what Europe was once like.
A land of endless wilderness where large animals roamed far and wide.
At this time of year, polar bears, on average, succeed only once in 20 hunts.
If the hunter is skinny like this one, that may not be often enough.
All she can do is keep trying.
To prevent her scent betraying her, she makes a wide sweep to get downwind of the seal.
Getting close.
She's now right behind the seal.
Incredibly, she caught the seal underwater.
It's only small, but even so its blubber alone will contain 100000 calories, enough to sustain this bear for a week.
And in that time, she might even catch another.
But this can't go on forever.
As summer continues, temperatures are rising.
Each hunt requires more energy. draining the bears of their reserves.
One of the most successful snow animals is solitary and lives most of his life alone.
They can be found in the very far north of the Arctic, the polar bear.
This male, like every polar bear, is almost completely covered in fur.
But his secret to staying warm in this frozen land is actually inside his large body.
He has a huge layer of insulating fat, about 10 centimetres thick.
It traps heat, keeping him warm from the inside.
To maintain this fat, he relies on his good hunting skills.
His prey is hidden under the thick ice.
Luckily, he has a secret weapon to help him hunt.
An extraordinary sense of smell.
A hundred times stronger than ours.
He can detect a seal carcass from 30 kilometres away. and under a metre of snow.
Success.
He will eat all the fat of a seal first, often leaving the actual meat.
This extreme fatty diet would kill us, but for the polar bear, it's essential.
Indeed, they are one of the fattest mammals on Earth.
Their incredible insulation and intense sense of smell make the polar bear a master in the snow.
They're also built to move around effortlessly in this snowy environment, unlike me.
I am a perfect example of an animal that is not adapted for walking about a snowy environment like this.
I'm 12 stone, 12 and a half stone, and all of my weight is distributed onto my feet.
Size 12, big feet for a human but not big enough to stop me from sinking down into the snow.
What I need to do is increase that surface area, put on some snowshoes.
I suppose the secret to moving around in deep snow is to do it efficiently.
There we go.
Adapted for walking in the snow.
That is so much better.
It's easy.
I can walk through the forest.
I'm not sinking down into my waist.
I can go fast.
I can almost go silently.
Like I belong here.
Polar bears have built-in snowshoes.
Their paws are wide, measuring about 30 centimeters across.
This helps them to distribute their weight evenly on thin ice.
Underneath their large paws are small soft bumps to give them extra grip on the ice.
This mother has three young cubs, just eight months old.
It's autumn and the family needs to fatten up before the winter hibernation.
This year, the oak trees are laden with acorns, an important source of fat.
The bears have plenty to eat, but their challenge here is finding enough to drink.
The limestone mountains soak up the rain, so there are no permanent streams.
Fortunately for the bears, there is another source of water.
Serranillas del Burro is prime cattle country and the ranchers provide year-round water for their herds by tapping into underground springs.
The water tanks are a magnet for all.
Mother bear with her young calves must approach with caution.
Bears occasionally kill cows, so the ranchers let their cow's horns grow long as a natural bear deterrent.
The family gets the message, loud and clear.
The cattle have had their fill.
Now it's the family's chance.
But someone else has got his eye on the tank.
A big male.
He's best avoided.
This male wants more than a drink.
He wants to cool off in his tub. she needs to put food in the mouths of her two young cubs.
There's a bitter winter coming, and if they're not well fed, her cubs won't make it through.
This is a hard place to be a mum.
The family is not alone.
This peninsula is home to 200 brown bears.
It's one of the most densely packed populations in the world.
The salmon bonanza has attracted others here too.
Nobody lives permanently in this remote part of Hokkaido.
But one hardy group have special permission to stay here for some of the year.
Hokkaido is Japan's second largest island, but the harsh conditions mean it's home to only 4 of its people.
Shirotoko is one of the loneliest corners, where you have to live close to the wild.
Brown bears can weigh 300 kilos and are not to be messed with.
When bears and humans cross paths, things can get dangerous.
But here, something astonishing has happened.
For the fishermen, bears have become a part of everyday life.
It takes some nerve, but the men live alongside them as equals.
Tough characters side by side, both dependent on the summon run.
The mother bear knows what she's doing.
Survival is in her blood.
Her ancestors came to Hokkaido from Siberia, and they walked here.
12,000 years ago, Hokkaido was joined to the Russian mainland.
Siberian animals colonized it before the sea levels rose, turning Hokkaido into an island.
It's why the wildlife here is so different from the rest of Japan and so well equipped to face the coming winter.
Initially, this was just a stopover as he ventured east.
But the creatures on Sulawesi were so curious and unique, he returned a further three times.
This amazing island is where I pick up his story.
And with the help of my guide Bobby, I'm searching for a tree-dwelling creature that would become a key piece of his evolutionary puzzle.
So, Bobby, how do you find a bear couscous?
Oh, I can smell.
You can smell it?
Yes, yes.
I can smell it.
The pee was very stinky.
The pee?
Yes, very stinky.
All right.
So it's a very strong... Very, very strong, yes.
All right.
OK.
Let's see if we can sniff one out.
Oh, up here.
Oh, yeah, got it.
You got it?
Yeah.
That's the first time I've ever seen one of these creatures, a bear couscous.
And they are quite extraordinary.
They're unique.
You only find them here in Sulawesi.
I've seen other kinds of couscous throughout Indonesia.
But this one is the only one that moves around during the day, so it's a lot easier to see.
His face resembles quite a cross sloth.
You know, sloth's quite benign, almost sort of sleepy looking.
But these look just like they're angry about something.
And in fact these are supposed to be active during the day, but I mean, that's not really active, is it?
He scratched his ear once.
That's really at the low end of active.
What excited Wallace about this lazy couscous is?
It's a marsupial, a relative of Australian mammals like kangaroos that carry their young in pouches.
And these weren't the only Australian creatures on this island.
He also came across Australian birds like cockatoos.
Wallace was starting to see a pattern.
