Across the Earth, creatures begin to sense secret signals...
...begin to move.
There is change in the length of day, and of night...in air temperature
and weather...foreshadowing a great upheaval ahead.
On a planet constantly in motion, swept by relentless seasonal change,
life too must move in order to survive.
Miracles of nature are about to unfold.
Each summer an extraordinary migration is fueled by millions
of tiny eating machines.
Gorging themselves on milkweed, they grow large enough for transformation...
from caterpillar...into one of Nature's most sublime creations:
the monarch butterfly.
Generation by generation, waves of monarch butterflies will migrate
northward through the United States as far as southern Canada.
As many as four generations are produced each summer.
The fourth generation appears no different from those that
preceded it, but it is.
Instinct tells it not to mate but to accumulate fuel urgently,
loading nectar through a straw-like proboscis.
This generation will live at least eight times longer than
its predecessors, enabling it to complete the longest and greatest
insect migration on Earth...
Using prevailing winds when possible, they labor to cover
about 100 miles a day.
Escaping the northern winter, they navigate toward a place
last visited by their great-great grandparents.
Converging from across two-thirds of North America, as many as
half-a-billion sweep southward toward central Mexico
on journeys of up to 2,500 miles.
Only one in five survives the hazards of the long migration,
but their numbers are so vast: a hundred million complete the journey
...arriving each year in the same small patches of mountain forest
that ensure their survival through winter.
How something the size of a leaf, can navigate across an entire continent
to a place it has never been, remains an unsolved mystery of nature.
The return of the monarchs holds mystical significance.
It is the Mexican celebration of the Day of the Dead.
In cemeteries, villagers gather with incense and candles to welcome back
the souls of departed loved ones...
Because the arrival of the monarchs coincides with the Day of the Dead,
many villagers believe the spirits of their loved ones are
returning on the wings of butterflies.
In the forest above the village, the last of the monarchs have arrived.
Through the winter they hang almost motionless in semi-dormancy.
A single tree may be blanketed by tens of thousands...
so many featherweight creatures their combined mass can break the branches.
Their winter homes are today protected reserves
...but to local schoolchildren they seem like magic forests.
They will fly only when warm enough.
A gentle breath is all it takes to trigger a cascade.
As spring approaches, the northward migration must begin.
lt is time at last for this generation to mate.
The females lead the great exodus... carrying their fertilized eggs
toward the North American heartland...
each carrying as well the secrets of how a distant future generation
will finds its way back, and complete a migration
as mysterious and wondrous as any on Earth.
Of all nature's migrators, none travel farther
or in greater number than birds.
Their preparation is intense. The young of species like Canada Geese
must grow enough in summer to migrate with adults by autumn.
Aviation fuel in the form of fat must be packed on
to power the flight ahead.
Some grow so heavy they can barely take off.
But when ready, they grow restless and eager...
Signals only they can decipher tell them when the weather
and winds are most favorable
...signals that propel them irresistibly forward,
to join one of Nature's greatest spectacles.
Traveling mostly beyond our view, migratory birds have eluded our
understanding since earliest times.
Today, radar designed to track Aircraft and weather has begun
to peer into their rarely seen world.
Researchers have confirmed that most small birds migrate at night...
and that many species save energy by riding storm winds
and prevailing air currents.
Radar studies have also disclosed flight speeds, travel routes
and flock sizes...and revealed that birds migrate in greater numbers
than previously thought, over distances once unimagined.
Five billion birds migrate each year from Europe deep into Africa,
and similar throngs cross Asia and the Americas.
To find their way, birds employ a remarkable array of techniques.
lnitially, instinct points them in the right direction.
Where possible they follow landmarks.
Where there are no landmarks, they turn to compasses provided by nature.
Many take their bearings from the sun's position.
The billions of night flyers seem to orient to the sunset
in the west as they set out.
Night offers protection from predators and smoother,
cooler air for easier flight, but somehow they must navigate
through the dark. Like early pilots, they simply
use the stars as a compass and fly toward familiar constellations.
When clouds obscure the stars, an internal magnetic compass
may guide them. Occasionally, the Earth's magnetic field is
visible to us in auroras, but only in the polar skies at night.
Some birds use a magnetically sensitive substance in their heads
to detect the pattern of Earth's magnetic field...and to follow it
like a map in the sky.
Equipped by nature with a remarkable array of navigational skills,
using whichever best guides them moment to moment,
birds are the master navigators of the animal kingdom...
The cold nutrient rich waters of the northern Pacific provide
an abundance of food for migrating sea mammals.
But when winter arrives, many leave here and swim great distances
to accomplish another common goal of migrations
to mate and give birth in places of safety and warmth.
So strong is this compulsion, gray whales make the longest migration
of any wild mammal...swimming nonstop day and night without feeding
for up to two solid months...from as far north as the Arctic Ocean
5,000 miles south to Mexico.
They may navigate through dark and murky seawater
using a primitive echolocation system.
Like submarines, many whales beam out and receive echoing sounds
that sketch acoustic images of the undersea terrain.
Traveling near shore, grays sometimes spyhop...
...perhaps to locate familiar coastal landmarks.
They maintain their bearings simply by keeping the sound of the surf
to their left going south, to the right returning northward.
Pregnant females lead the migration south in order to reach
Mexico before giving birth.
Unfortunately, the timing is not always perfect...
L. A. County lifeguards were the first to reach the 13-foot-long
infant gray whale. Experts tell us it's a female and they think she's
less than a week old because part of the umbilical cord is still attached.
It's said the mother may have started south late, giving birth along the way
to an orphan now badly dehydrated and malnourished.Rescue efforts are now
underway to bring the baby whale out of the water and transport her
to an emergency care center at SeaWorld in San Diego, two hours away.
I needed to drive as fast as I could, as fast as the truck would go
and I knew time was of the essence. And then the CHP would just zoom on
right ahead, close off traffic and let this whale go on by.
When I first saw the whale, I honestly didn't think
that she was alive. We see animals like this all the time,
and the majority of them come in and die very soon after,
or arrive dead.
They name her ''JJ'', and begin round-the-clock care.
They must quickly learn how to take the place of a mother whale.
It was amazing. As soon as the warm milk reached her stomach,
she calmed...as if she recognized that we were here to help her.
She was still semi-comatose and my assessment at the time was that
that animal had almost no chances of surviving. She was in very bad shape.
While JJ's fate resides in the hands of human keepers, most of the
gray whale mothers have made it to the warm, protected lagoons of
Baja California before giving birth.
The regularity of their migrations Once made them easy prey for whalers.
Now, they are greeted like Celebrities by adoring fans
yearning to touch a real whale.
Protective laws discourage boaters from approaching a whale...
...but no law prevents a whale from approaching a boat.
Naturalist Sherri Bondi and her daughter are here
for just such an encounter...
My little girl, Selenita, the little mermaid, has
a very special connection to the whales.
When I got out there it was just like, whoa...
One was coming straight for us and I'm like what's that whale doing?
Lookit, Mommy.i
Oh, look at the eye, look.
They seem to really study us carefully. I often wonder
what they're thinking about while they're gazing at us,
as I gaze at them.
Most whales are shy and keep their distance. But a few are curious.
Occasionally a mother whale will bring her baby to the boats,
in what seems like an attempt to introduce it to the human visitors.
Because of the protected nature of the lagoons we don't have predators
who prey on the baby whales.
They stay in the lagoons for about two months while the calves nurse,
and they nurse all day long and all night long, and they grow very quickly.
They can double in weight from when they're born - they're about
a ton when they're born and about 15 feet in length.
The mothers start to teach them swimming skills in what I call
swimming schools. they'll swim against the tide in order to
strengthen their flippers to make the long migration north.
She spit water at you.
I was really wishing I would touch a whale.
I'm like'Oh, I hope I touch him and all of a sudden my hand was really down...
I touched it.i
It was just...a miracle?
In late spring, when the calves are strong enough, their mothers will
lead them on their first great voyage north to feast in the polar seas.
One youngster has missed that first migration, but 14 months after
her rescue the orphaned calf JJ, gorges on 500 pounds of seafood a day.
Once nearly lost, she approaches adult size.
She pushes against the northwest corner of her holding pen day after day
...seemingly eager to rejoin her own kind on their journey northward,
unaware that such a rendezvous is now only two weeks away...
One of the most bizarre migrations in nature occurs on tiny
Christmas lsland - a thousand miles west of Australia
in the lndian Ocean.
Each year as the monsoons arrive, rainy season and lunar cycle
combine to unleash the breeding urges of forest creatures
that emerge like...
...monsters in the night.
A hundred million red crabs begin their annual march from woodland
to sea to mate and spawn...
The island's one thousand human inhabitants miscalculated
the location of their community, building it smack in the middle
of the largest migration route.
But the crabs are harmless, and the islanders adopted a strained
but friendly relationship with their fellow residents.
After a journey of up to three weeks, males reach the shore first,
where they confront an obstacle course of jagged limestone cliffs
undercut by powerful seas.
Nature itself can seem booby- trapped with hidden surprises...
On terraces above the cliffs, the males prepare burrows
as they await the females. When the females arrive
a few days later, they promptly take baths to replenish moisture
lost on the journey...and perhaps to rinse away the grime of travel
and enhance their feminine allure.
When ready, they approach the burrows...
where they are seized by the males in a mating embrace.
After mating, the males will depart for the interior forests again,
leaving the females in protective burrows
as their now-fertilized eggs develop.
The females know precisely the right moment in the lunar cycle
to amass at the sea's edge.
The high tide of the last quarter moon is about to crest.
Each carrying up to a hundred thousand eggs,
the females head for the surf...
...where they discharge their eggs into the outgoing tide.
The young will spend three weeks at sea as marine larvae
before returning as baby crabs. But adults are no longer able to swim.
The mothers risk their lives discharging their eggs.
Those swept away will drown.
The surviving females head back to the woodlands, leaving the fate
of the next generation to the whims of the currents...
...and the predators of the sea.
On the plains of East Africa, migration holds the promise of life...
...and the prospect of death.
Here, life is a relentless confrontation between hunter...
...and hunted.
Yet survival is also determined by the seasons.
Through the wet season, zebras and other grazers are sustained
by rich grasses and abundant water.
For them, and the hitch-hiking Oxpecker birds,
this is a time of plenty. But soon drought will wither
the plains, changing the lives of both predator and prey.
For two-hundred-thousand zebras it is time to begin
their migration northward.
At times leading the great migration, zebras are
joined by more than a million wildebeest.
It is the largest migration of hoofed animals on Earth.
The two species find safety in numbers and in mutual vigilance...
the alarms of each alerting the other to the presence of predators.
There is another kind of threat...
Range fires race across the tinder-dry plains, a signal
that drought has parched the land. Thirst becomes a driving force.
The herds will risk drinking even from pools where crocodiles wait.
The wary zebras remain on high alert.
But a young wildebeest does not sense danger's approach.
Reaching the northern grasslands the herds confront
the unrelenting reality of Africa: there is no safe haven.
It is very rare for a hyena to attack an adult zebra.
Foals, are easier.
A mother is lured away to a defensive position...
unaware that other hyenas approach from behind.
The father races to the scene.
One very lucky foal will live on.
Others are not so fortunate. For those whose existence
depends not on grass but meat,
zebras are a river of passing food... a guarantee of their own survival
in a harsh world.
Many are lost...but those that survive will grow strong...
and one day will race across the African plains
in the great migrations to come.
Sharing these grasslands with the migrating herds are grazing animals
whose history has followed a different path.
Their story is closely linked to that of anotherspecies that arose here.
Once seasonal migrators, following the herds they hunted,
some humans in Africa long ago turned instead to the herding
of domesticated animals.
No longer compelled to pursue wild prey like zebras,
they were able to establish settlements.
Today, like countless humans elsewhere, the Maasai and Datoga peoples still
lead their herds from protective corrals to pasture and back each day.
Yet in the time machine of East Africa there are still
tribes who follow the seasons.
The Hadza possess neither shelters nor livestock to restrict their movements.
Employing simple tools and weapons, they choose instead to continue
pursuing the wild herds.
They are rare living remnants of the tribes who left these plains
100,000 years ago to embark on what would prove to be
the greatest of all migrations!
They were the ancestors of all modern humans.
Their mastery of fire, weapons, tools and clothing gave them the ability
to survive almost anywhere, making possible a new kind of migration...
Small bands of hunters would venture northward out of Africa
into the world at large.
They set out not on round-trip, seasonal journeys...
but on a one-way migration that has lasted 4,000 generations...
...a migration that would take them to the very ends of the Earth.
Then in a geological eyeblink, our species and our technology
radically changed the face of the planet.
Our blazing success has darkened the lives
and blocked the journeys of many other species.
But today we have come to understand that our own existence
is closely linked to that of the creatures around us.
We turn from the hunters we once were... ...to the protectors we are becoming.
We cannot really hope to know most wild creatures in their worlds...
but occasionally one animal crosses into our world and touches our hearts.
The time has come for ''JJ'' to go home, to rejoin her own kind
as they embark on their migration northward.
Her story has become a media event, her plight a concern to millions.
And now she is carried homeward as carefully as if
she were one of our own.
Sometimes a single creature we come to know can stand for
all the billions we cannot know.
And in our concerns for one, we discover how much we treasure all.
On tiny Christmas lsland, millions of baby crabs are returning
from the open ocean, fulfilling the purpose of their parent's migration.
Now they begin the first of their own great migrations...
from the nursery of the sea to the home of their species
in the forests above.
In marshlands and lakes on every continent, in wave after wave
of triumphant landings, billions of birds reach their journeys end at last.
On a planet constantly in motion, life too must move
in order to survive.
Season by season, creature by creature,
miracle by miracle... ...the epic journeys continue.