This is the tundra.
Even trees struggle to take root in the icy soil.
But life is possible even here.
An arctic ground squirrel.
He spends his entire winter asleep.
Out like a light for eight months straight...
the longest, deepest hibernation of any animal on earth.
This extreme lifestyle can only be seen using a special filming burrow.
He's pretty much stopped breathing.
His heart is barely beating.
The sun is getting higher every day.
In the darkness of his burrow,
the squirrel's body clock drags him out of bed.
There's no time to waste.
Last time he saw it, back in the autumn, this was his territory.
Now he's got to fight for it all over again.
For the next two weeks, he'll barely have time even to eat.
It's a constant battle to keep rival males of his turf.
There's a sense of anticipation in the air.
Females emerge a few days later.
He won't want to miss his first date.
And there she is.
But what's he doing?
She'll only be fertile for 12 hours in the entire year.
There's no time for hesitation.
He cautiously makes his move.
She might be in a hurry, but she can still be choosy.
He knows that while there are other males around,
she could easily go off with someone else.
So, he won't leave her side for 24 hours.
An Alaskan spring moves fast and if you don't seize the moment,
it will pass you by.