Hostile Planet

Bear grylls: Growing up on the savanna,

This calf will face many dangers.

But a battle this big is incredibly rare.

Two evenly matched testosterone-fueled bulls.

No place for a baby.

One day the calf may have to fight like this.

But there are far more imminent threats.

A third of all calves don't make it

Through their first year.

Like all animals here,

His fate depends on the grass growing under his feet.

Grasslands cover a quarter of the land on the planet.

They support the largest animals

And the biggest herds to walk the earth.

Life on the these great plains may look easy...

But don't be fooled.

When conditions turn,

They can become some of the most volatile landscapes

On our planet.

A relentless cycle of flood...

Famine...

Freeze and fire.

And as our climate becomes more unpredictable...

It takes the animals of the grasslands to hell and back.

Deepest winter on north america's great plains.

40 below...

And record snowfall.

Bison dig deeper for diminishing returns.

Dead grass with the nutrition of cardboard.

23 pounds of the stuff every day still isn't enough.

They're starving.

The calves are the most vulnerable,

And if the cold doesn't get them, another enemy might.

Winter is a wolf's ally.

A time to feed off the suffering of others.

These are the biggest wolves in the world.

And at 25 strong, they're one of the largest packs.

Size matters when you hunt giants.

Ten times heavier and well armed,

The bison are stronger,

As long as they stand their ground.

But wolves create panic.

Running for the woods is a mistake.

Trees break their formation

And expose the weak.

Alone, a youngster is an easy target.

But a mother will risk her own life to save her calf.

They must make it back to the safety of the herd.

But deep snow saps the bison's energy.

Again, the calf is isolated.

Again, it's rescued.

Now there's hope.

As long as the calf can stay hidden within the ranks...

While the snow remains, the bison get steadily weaker.

But on the grasslands,

Change is inevitable and often extreme.

By April, it's 100 degrees warmer

Than at the start of the year.

And a new danger is brewing.

Grylls: Spring, and the start of storm season.

North america's great plains are a hot spot

For some of the most intense thunderstorms on earth.

Some mutate into supercells.

Monsters with the equivalent energy of 100 nuclear bombs.

Storms are becoming more frequent here.

And in grasslands across the globe,

Weather patterns are increasingly erratic.

Here the rains are a month early and hitting hard.

Over a year's worth of rain in just a couple of months.

Enough to transform the grasslands beyond recognition.

The worst flood in 50 years.

Four feet of water.

Not a problem for the adults,

And plenty of fresh grass,

But a bit deep for a calf.

Luckily, he has a snorkel.

These floods may complicate things

A little in the short term.

But they'll revitalize life on the savanna.

As the flood waters subside...

...They reveal a flush of new growth.

And fuel a baby boom.

But this can be a dangerous place to take your first steps.

It's home to more large predators

Than anywhere else on earth.

Many thomson gazelle fawns won't survive their first hour.

Their only hope is to hide.

Mothers clean their newborns

To remove any scent,

But for this fawn