- [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.
Their epic journey takes place in East Africa.
A migration loops through Kenya and Tanzania
of about 600 miles.
Two mighty rivers intersect their route,
and the herds have to cross.
Crocodiles have one month to capitalize
on this feeding opportunity.
Then the migration moves on,
gone from the rivers for another year.
Each river has a distinct personality.
The Grumeti is narrow, slow flowing and irregular.
It's a bit of a chameleon,
changing with the seasons
and promising surprises around each bend.
It's tough to hunt here.
Crocodiles in this neighborhood must be hardworking
and flexible to master the different hunting strategies
required of each zone.
(dramatic music)
Things are different on the Mara.
This is where the privileged live.
A fast-flowing, deep river with steep banks.
The Mara is consistent along its entire costs.
Wherever the wildebeest choose to cross,
the zones are the same.
Mara crocs must be deep water specialists,
but nothing happens in the trenches without the herds.
(dramatic music)
They are about to arrive and every crocodile knows it.
- [Narrator] Just beyond the meadow,
10 million straw-colored fruit bats now live in the swamp,
all squeezed into half a square mile.
This is one of the largest known gatherings
of fruit bats in the world.
And in terms of numbers,
it's the largest mammal migration on Earth.
(bats screeching)
This one special patch of moist evergreen forest
provides the bats with a comfortable home
during the heat of the day.
They jostle for roost space
using a hooked claw on their wingtip to grip and climb.
Gingery bodies and pointed faces
give the bats the nickname, flying foxes.
(bats screeching)
Each bat is about eight inches long,
but has a wingspan of two and a half feet.
The wings are formed from a membrane of skin,
criss-crossed with a network of hair-thin muscles,
which control stiffness and shape.
Unlike insectivorous bats,
fruit bats don't use echolocation,
but rely on vision instead.
- [Narrator] This small buffalo calf,
just four months old,
follows his mother through Zambia's Luangwa Valley.
He's part of a huge herd.
1,000 strong made up of 50 families,
all sticking together for protection.
There's safety in numbers,
but keeping such an enormous group together is hard work.
Getting separated could be disastrous,
especially for the young buffalo.
(suspenseful music)
But the herd has a strategy to maintain cohesion.
A few, go up front as trusted pathfinders,
leading the others to fresh grass and water.
These aren't necessarily the most dominant
or oldest animals,
but it's always the same select few that take on this role.
(soft music)
Where these buffaloes go,
the others follow.
(buffaloes grunting)
But the level of organization goes further than that.
A calf is kept safe in the center,
along with his mother and the other breeding females.
(soft piano music)
More expendable,
bachelor males and the sick or injured
are pushed to the periphery.
Like the pathfinders,
those on the edges are always on the alert.
(suspenseful music)
And they've spotted danger.
A lion is stalking the animals at the tail end of the herd.
When one buffalo runs,
herd mentality kicks in and they all make a move.
(suspenseful music)
This time an adult male,
who was bringing up the rear has been taken down,
but the calf is safe.
The herd strategy has worked well.
By saving the young ones,
the future of the group has been safeguarded.
- These are the Oyamel fir forests of central Mexico.
This unique alpine habitat is a relic from a time
when the Earth was cooler and wetter.
Now only 2% of the original fir trees remain.
Their bows are heavy,
but not with leaves,
with millions of Monarch butterflies.
(soft music)
These individuals belong to a super generation.
Survivors of an incredible 3,000-mile journey
that began in Canada and the Northern United States.
They arrived five months ago and have remained motionless
through the winter in a state of dormancy.
Like a hibernating bear,
they require the warmth of spring to awaken.
(soft music)
As the sun's first rays strike,
there's no time to waste.
They take to the skies
in the millions.
(soft music)
All synchronized to find a mate.
(soft music)
For the females, there's no shortage of options.
(soft music)
But for a male Monarch in Mexico,
finding a partner means the ultimate sacrifice.
Whether the males succeed or not,
it's their last week on Earth.
This is a male,
easily identified by the two black spots on his wings.
He needs to mate, and soon.
His luck is in.
A female,
and she's alone.
(soft music)
He whisks her away from the surrounding chaos,
then injects her with sperm.
He also donates a cocktail of nutrients
to assist her in pregnancy
and her long journey ahead.
He loses up to 1/3 of his body weight in the process.
An overzealous male can overdo it
and cause a female to explode.
Not this time.
Now carrying hundreds of fertilized eggs,
this female and millions of others like her
must embark on the second leg of their epic migration.
(soft music)
They'll fly 900 miles back north,
through Mexico and into the United States.
There, they'll find food and a safe place to lay their eggs,
which will give rise to the next generation
to continue the journey north.
(soft music)
As for the male, his journey ends here.
His mate has literally sucked the life out of him.
But his great, great grandchildren
will be the next super generation,
the ones strong enough to fly 3,000 miles back
to these ancient fir trees of Michoacan.
- [Narrator] The manatee,
these gentle giants can't tolerate water temperatures
below 68 degrees for very long.
They move inland,
seeking out the warmth of Florida's natural springs.
The hotspot on the Gulf coast is the Crystal River,
where hundreds gather each winter.
(dramatic music)
It's a similar story over on Florida's Atlantic coast,
but it takes a little more work
to get to the springs from here.
This female left the ocean behind a couple of days ago.
She's on a journey through rivers, lakes, and canals,
to reach a winter Shangri-La,
deep in the heart of the state.
It's more than 100 miles inland
to reach the warm water springs,
but she has no choice.
If she remains in the ocean,
she could develop hypothermia and die.
(dramatic music)
At around 1,200 pounds, she's no lightweight,
yet surprisingly, manatees have relatively little body fat
to protect them from the cold.
(dramatic music)
On the third morning of her journey,
she reaches her destination,
Silver Springs State Park.
It has a mystical beauty in winter.
(dramatic music)
Steam rises as moisture from the warm river evaporates
into the cool morning air.
(soft music)
Millions of gallons of pristine water from the springs
feed into the silver river every day.
(soft music)
Best of all, the water is a constant 72 degrees.
Perfect to fend off the chill
for this weary winter nomad.
(soft music)
Here, she can rest and eat her fill of aquatic plants
until spring calls her back to the ocean.
(dramatic music)
- [Narrator] A winter blizzard in Yellowstone
is a singular collision of mighty forces.
Snowfall accumulates in staggering depths.
(dramatic music)
Few species are prepared to withstand these conditions.
(suspenseful music)
But 2 million winters have shaped a creature,
who attempts to survive here long after others have fled,
(suspenseful music)
the bison.
A muscular hump from supports a massive head,
a snowplow that clears away drifts
and uncovers buried grasses.
A dense coat and layers of fat
stave off the punishing wind and cold.
These beasts carry winter with them, every step.
They're the descendants of survivors from a past world.
The conquest of the continent
nearly spelled the extinction of their species.
In the 1800s, as America expanded westward,
herds that numbered in the tens of millions
were slaughtered.
By the late 19th century,
only a few hundred bison remained.
The last free roaming herd lay hidden
in a remote valley in Yellowstone.
(dramatic music)
These two dozen bison became the source
for the recovery of the species.
(dramatic music)
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)
As darkness falls,
the herd leaves the valley,
marching towards the heart of Yellowstone's warmth
and the possibility of relief.
(soft music)
- [Narrator] A flock of pelicans
creates a wave of motion and sound.
They signal the true wealth
of the iSimangaliso Wetland Park.
The park supports 500 bird species, including flamingo.
At least 48 avian species call it home.
It's their breeding ground.
Here, migratory birds stock up on rich shrimp and mollusks
on the mud flats before heading back out
on what is known as the East Coast Flyway.
(soft music)
The United Nations declared the park
a world heritage site in 1999.
(soft music)
The biodiversity here is hard to match.
(soft music)
(upbeat music)