(dramatic music)
- [David] 60,000 years ago,
humans left Africa for the first time.
Since then, we haven't stopped,
traveling to every corner of the Earth.
But our journey is just one of many.
At any given moment, billions of animals are on the move
and the health of our planet depends on it.
(dramatic music)
Migration is the most vital survival strategy
(dramatic music)
whether to feed,
to breed
or to find a new home.
(dramatic music)
And it's not without risk.
This series traces extraordinary journeys
in a world that is changing faster than ever.
And only now are we beginning to understand
that all life on Earth depends on the freedom to move.
(dramatic music)
Every year, this land in Botswana is transformed.
These scars are the only sign
that it was covered by water just three months ago.
Then rich and green, now baked and barren.
(wind roaring)
This change drives animals to move en masse.
(buffalo snorting)
(dramatic music)
Cape Buffalo are marching across the Kalahari Desert
towards the last remaining water
(dramatic music)
Groups have come together and formed a mega herd.
(buffalo snorting)
The largest in Africa.
(buffalo snorting)
All are making the same annual pilgrimage
to one remote marsh.
And others are relying on them to do so.