- [Narrator] Yellowstone is now home to thousands of bison.
They wage an ancient battle with the storm.
But each winter that comes a time when the snow gets too deep for these animals to find forage, the bison begin to stir to rearrange themselves.
(dramatic music) A matriarch, the leader of the herd, gives a signal.
It's time to move.
(dramatic music) Guided by instinct and experience, the bison fall into line to follow her trail.
(dramatic music) This is the beginning of their migration.
(dramatic music) - [Narrator] The numbers are staggering.
Over a million wildebeest and thousands of zebras drive forward in a never ending search for food and water.
The pathways indelibly etched into the landscape.
