Original subtitles

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NARRATOR: Twice each year,

in Canada's frigid north,

millions of caribou

embark on an epic journey,

the largest mass migration

of any mammal walking the earth.

On the California coastline,

massive elephant seals meet to breed

and battle after months at sea.

Monarch butterflies flutter thousands of miles

in a multi-generational marathon.

These creatures survive incredible migrations,

overcoming deadly obstacles,

crossing oceans and continents,

to ensure the future of the species.

Inside the different realms of the wild kingdom,

members of a single species

assemble in droves,

one flock,

herd,

or troop

reigns supreme.

These are the world's great...

NARRATOR: Nunavik,

the most northern reaches

of the Canadian province of Quebec.

This is the tundra,

a wild, empty expanse of land.

But it won't be empty for long.

It's late August; a restless time here.

This caribou is heading south.

Sometimes called reindeer in other parts of the world,

caribou got their name from a Mi'kmaq First Nation's word

meaning one who paws at the ground.

They scrape the ground with their hooves

to dig up lichens

that comprise the bulk of the caribou's diet.

He stands five and a half feet tall at the shoulder,

the third largest member of the deer family.

He spent the past five months

in the farthest northern reaches of his range.

But as the days grow shorter,

it's time to move on,

to sparse forests called taiga,

hundreds of miles south,

where he will spend the winter.

And he's not alone.

This is the Leaf River herd.

It's an animal empire on the move,

the largest caribou herd in North America,

estimated at 330,000 animals.

The herd marches in long strands

stretching for miles

on wide expanses of open land,

coming together at narrow passes and obstacles.

And The Leaf River herd is only one of many.

Millions of caribou migrating to cross the tundra

each spring and autumn.

The greatest land migration on earth.

Caribou are an important cultural and dietary keystone

to the people of the North.

One Inuit story says the first woman on earth

dug a hole in the ice to fish.

From the hole, she pulled every animal in the world,

the last to come was the caribou.

She ordered the caribou to multiply.

Soon they covered the land.

Enough caribou to feed all of mankind.

Unlike other deer,

both male and female caribou can grow antlers.

But only some does grow them,

and they're proportionately small,

compared to most deer.

The males are much larger,

for jousting with other bucks.

Only the moose can boast a more impressive rack.

Three months ago in spring,

the Leaf River herd moved north.

The females led the migration,

searching for the perfect place

to have their babies

far away from forest predators like wolves.

Now as winter closes in,

food in the North is becoming scarce.

They've got to move.

They'll be bringing a new generation with them.

There's not much time to grow up.

At just two weeks old, these fawns must struggle

through their first southern migration.

With junior in tow,

the return will be far more dangerous,

and slow going.

The treeline is hundreds of miles away.

The survival of the empire

depends on the females' ability

to get their young back to the forest alive

before winter.

Each day presents mortal danger.

Death could come in the form of broken leg,

or a prowling bear.

Or it could be something even bigger,

like a river.

NARRATOR: On the coastline of Southern California,

these rocky beaches are where a giant of the sea

returns after a migration of its own.

Elephant seals are named for the fleshy proboscis

on the massive mature males.

They're colossally large,

with a big bull weighing up to 5,000 pounds,

about as much as an SUV.

The females are much smaller than their mates

weighing up to 1,300 pounds.

That's still more than a dairy cow.

Twice a year, northern elephant seals

migrate out to sea,

then return to the beaches where they were born.

They travel further than any other seal,

more than 2,000 miles.

The reason for their long journey is food.

Males and females have different dietary requirements,

so they go to different places.

The males stick closer to the coast,

and head north to feeding grounds off Washington State,

British Columbia and Alaska.

They prefer to dine on small sharks and rays

in shallower waters.

The females go further into the open ocean.

They've been spotted as far west

as the Hawaiian Islands.

They prefer to feast on open water species,

especially squid.

While at sea, the Northern elephant seals

forage for food almost constantly,

they may not even stop for sleep.

They spend most of their time underwater.

Elephant seals dive deeper

than any other species of seal,

and can hold their breath

for up to an hour and a half at a time.

But if there are to be baby elephant seals,

male and female must meet somewhere,

and this is the place.

Point Piedra Blancas, near San Simeon California.

It's September.

Elephant seals are beginning to congregate

on beaches and rocky outcroppings like this

all along the coastline of California and Mexico.

It's called "the fall haul-out".

The seals arrive at different times

depending on their age and sex.

Last year's pups, juveniles and sub-adult seals

are returning to the rookeries of their birth.

These males are five years old,

just hitting puberty.

Their noses haven't grown to their full fleshy length yet.

They won't grow to full size and maturity

until they're eight or nine years old.

The females reach sexual maturity earlier,

at three or four years old.

These younger elephant seals are here

to rest and relax.

While on land they don't eat much,

learning to fast is part of growing up

for an elephant seal.

Adults don't eat at all during breeding season.

But it's not all fun in the sun.

The young males play-fight;

sparring practice for when they're older.

When they grow up, these battles

will determine who gets to breed.

They rear back their heads

and bellow through their undersized noses.

And go chest-to-chest, sizing each other up.

They bare their fearsome teeth,

but it's all for show, mostly.

The juveniles are still more bark than bite.

But when the big bulls arrive in a few months,

that's when the fighting will get serious.

NARRATOR: On the other side of the continent,

millions of winged creatures are about to embark

on another huge migration.

It is one of the world's most spectacular

mass movements;

undertaken by one of its tiniest

and most delicate creatures.

The monarch butterfly,

instantly recognizable,

a regal symbol of beauty and transformation.

Its migration is an intergenerational odyssey.

Each autumn, monarch butterflies migrate

from their summer homes in southern Canada

and the northern United States

to spend winter in warmer climates.

As summer comes in Nova Scotia's Annapolis Valley

on Canada's east coast,

a female is looking for the right spot to settle down.

She's looking for just the right plant,

the milkweed.

She's ready to lay her eggs,

up to a thousand of them.

As a caterpillar, the monarch doesn't stray far

from the plant where it was laid.

The caterpillar is voracious,

eating its own bodyweight in milkweed leaves every day.

The milkweed gives the caterpillar a toxic taste

that stays with it for life,

and keeps predators away.

The caterpillar feasts for about three weeks,

growing so fast it sheds its skin four times.

Now, the caterpillar seeks out a horizontal branch

to begin its final transformation.

It spits out silk from its lower lip,

creating a mat on the branch.

Then two of its back legs forge together

creating one appendage.

Tiny hooks latch onto the silk mat like Velcro.

Once its skin begins to peel, it's only a couple of minutes

before it sheds its fifth and final layer

of caterpillar skin.

The pale shell is a hard exoskeleton

called a chrysalis.

The very cells comprising the caterpillar's body

break down into a stewy goo

and then re-form.

A week or so later,

the transformation is complete

and the butterfly inside, is ready to emerge.

Free from its chrysalis,

the butterfly hangs for hours,

until its wings fill with blood,

dry, and stiffen.

If this butterfly were born in summer

it would live six more weeks,

during which time it would breed,

lay its eggs, then die.

But this is an autumn butterfly,

so after all this,

it still has a migration of thousands of miles ahead.

NARRATOR: In northern Quebec,

the Leaf River caribou herd's migration

meanders through the village of Kangirsuk.

The herd's route changes every year,

but the migration dates back millennia,

before there were any towns here at all.

It wasn't long ago that people here

lived out on the land,

following and hunting the herd.

Towns were built in the mid-20th century,

and the nomadic way of life

came to an end for most.

But the north is changing once again.

Caribou herds are shrinking everywhere.

The Leaf River herd is the largest left

in North America.

Even their numbers are down

more than a third in recent years.

The nearby George River herd

used to number nearly a million.

But in just two decades,

the population collapsed by 98%.

From 800,000 caribou

to just 15,000 today.

Nobody is sure why the herds are shrinking.

The likely cause is a combination of

commercial hunting, industrial development,

disease and deforestation.

In response, the Inuit have suspended their hunt

in the past few years.

It's the first time anyone can remember

that the Inuit haven't hunted the George River caribou.

Caribou are uniquely specialized

to survive here in the north.

The short, hollow hairs of their outer coat

provide insulation against the cold.

Their entire body, even their muzzle,

is fully furred.

Their long legs and huge stride

cover massive expanses of ground.

Even as babies, caribou are born to run.

At just one day old, a caribou fawn

can outrun an Olympic sprinter.

These fawns are just two weeks old,

and well into their first migration south.

Mother and baby form a bond from birth,

and recognize each other

by sight, sound and smell.

The fawns stay by their mother's side

as much as possible through the journey.

The route isn't easy.

The ancient paths lead to a place

where the open tundra tumbles down

a massive rock face.

The yawning valley of the Payne River

divides the landscape.

In open plains, the herd splits into smaller groups,

sticking mostly with members of their own gender,

in gatherings of a few dozen to a few hundred.

But here, there's just one safe path

from the highest elevation

down to the riverbank.

This is a bottleneck in the migration.

One by one, the herd trickles down the hillside

like a mountain stream.

A river blocks their path.

Rivers can be more dangerous than any predator.

Hundreds of caribou die

attempting these crossings every year.

It will take three full days for the entire herd

to cross this river.

Instincts and their stomachs

drive them on.

NARRATOR: It's December.

The big bull elephant seals

begin arriving on the beaches

of California and Mexico.

They've been at sea for at least three months,

bulking up for mating season.

It's a lot of work to haul their 5,000 pound bodies

out of the surf.

Blubber accounts for up to 50% of the male's body weight.

It keeps them warm in the frigid ocean

and fuels them during the hungry months on shore.

All that fat was almost the species' undoing.

When the California gold rush hit in 1849

there was a sudden spike in demand

for industrial lubrication for mining machinery.

Back then, that meant whale oil,

but whale populations had already been decimated.

Hunters turned their sights to the elephant seal,

and all but wiped out the species

in just 15 years.

In 1884, a tiny colony of seals was discovered

off the coast of Mexico.

It's believed all 100,000

northern elephant seals alive today

can be traced to that one group.

They come by their distinctive nose naturally.

But their pink chest callouses?

They earn those the hard way,

through years of battling with other males.

Bull elephant seals are fiercely territorial.

This one is patrolling the water snorting and blowing bubbles

to warn off any other males that approach.

Their noses also make great echo chambers,

booming out signals to other seals.

When mating season begins,

they constantly harass any females on the beach

until a pecking order is determined.

The moment a juvenile male starts getting too friendly,

a bigger bull comes in.

The fight breaks out.

Another male comes up the middle

to take his chance with the female.

As though that's not enough,

a fourth male decides to get involved.

The female slips away into the sea,

as the males fight it out on the beach.

It's rare, but these battles can be to the death.

Only one male can conquer a beach,

or a section of beach,

and mate with a harem of females.

Competition must be chased off

or beaten into submission.

There can only be one king of this empire,

the dominant male of the harem of this beach.

To the victor go the spoils.

A single male can hold a harem of up to 50 females.

It's evolution's way of ensuring

that only the biggest, strongest males

pass on their genes to the next generation.

NARRATOR: As August turns to September,

the monarch butterfly from Nova Scotia

begins its long trip south.

At first, it is a solitary voyage.

Individual butterflies gradually

fluttering their way southwest.

But eventually, it joins 150 million others,

the great-great- grandchildren

of those that flew north the preceding spring.

Remarkably, they make the incredible journey

in a state something like hibernation in other animals.

It's called diapause,

a slowing down of the metabolism.

It allows a single monarch to live long enough

to make the entire trip south.

The migration path follows a corridor

determined by flowering nectar plants,

air currents and climactic conditions.

Research suggests the butterflies use

an internal compass to navigate,

an operation involving both their eyes

and antennae.

Their eyes watch the sun's position in the sky,

which changes throughout the day.

Their antennae contain an internal biological clock

to determine the time.

The butterflies' tiny brains

compare those two pieces of information

to determine which direction is southwest.

They can be blown off course easily,

but gradually re-orient themselves.

Monarchs fly at speeds of 15 to 25 miles per hour,

overnighting together in clusters called roosts.

Landforms like mountains and coastlines

gradually funnel the scattered individual butterflies together

as they get closer to their winter homes.

The destination for some butterflies

is California's coastline.

Our butterfly from Nova Scotia

will flutter further south,

to the Oyamel fir forests of Mexico.

The arrival of the monarchs

in Mexico's interior highlands

coincides with an annual celebration,

D�a de Muertos, the Day of the Dead.

Traditional folklore says the monarchs represent

the souls of the deceased

returning to the earth for the celebration.

By December, monarchs cover the trees.

It's not the riot of color you might expect,

because only the monarch's dull outer wings are exposed.

A monarch butterfly weighs about a 13th of an ounce.

but they are so crowded,

tree branches can creak and break

under the weight of tens of thousands of butterflies.

The largest monarch overwintering sites

are in Mexico and California,

but smaller ones have been discovered

in Arizona and Florida.

Until 40 years ago, many of these places

were a secret to everyone

except the butterflies.

Now a few of the biggest ones in Mexico

are protected as world heritage sites.

Nobody's quite sure how the butterflies

chose these places,

but it seems to be a combination of the right trees,

climate, water supply, forest canopy

and isolation.

The migratory butterflies live to be six months old,

longer than any other generation of monarch.

That's because they put off breeding,

remaining in a state of perpetual adolescence.

The butterflies cluster together

to conserve heat.

They stay in a state called quiescence,

keeping still, and conserving energy.

Everything has to be just right

for the monarchs to survive.

If it's too cold,

they will burn through their fat supplies and die.

Unusually warm weather can stimulate them to breed,

and begin their northern migration too early,

flying straight into the frosty northern winter.

About half of all monarchs

that arrive in the wintering grounds

die before the return trip.

Cold snaps and storms can kill millions more.

In 2002, a snowstorm in Mexico

killed 500 million monarchs,

three times as many butterflies

than the entire migration consists of today.

Overall, the number of migrating monarchs

is down by 75% in the last 25 years.

But if everything goes just right,

these monarchs will stay here until March

and then begin their part of the journey home.

NARRATOR: Crossing rivers is a fact of life and death

for the caribou herds of Northern Quebec.

Their winter home in the forest

lays hundreds of miles past the opposite shore.

The adaptations that enable caribou to survive

the frozen northern winter

also help them in the water.

Adult caribou are strong swimmers,

their broad hooves and powerful legs

help them paddle through the water.

Short hollow bristles of their outer fur

keep them warm and increase their buoyancy.

The arteries and veins in a caribou's legs

are intertwined, so hot blood leaving the heart

warms the cold blood traveling toward it.

Their stout bodies and short ears

minimize their surface area

and exposure to the cold.

Still, strong currents can sweep

even an adult bull off-course.

And caribou of all ages must make the swim.

At only two weeks old, this year's fawns

haven't had much practice swimming.

If they get separated from their mothers,

no other female will adopt them.

Sticking together is a matter of survival.

A fawn separated from its mother,

calls out to her.

(GRUNTING)

(GRUNTING)

Mother turns back for her baby.

She positions herself downstream

to keep the current from taking her fawn again.

They've made it across,

but there will be more rivers

and other dangers to come.

Once they clamber onto shore,

they take a moment to rest

and feed for the journey ahead,

still hundreds of miles to go.

The caribou's future is uncertain,

both for this year's fawns

and the entire Leaf River herd.

Their forest destination will offer food and shelter

for the coming winter,

but there will be prowling predators too,

like bears and wolves.

At just two weeks old,

this fawn is still only halfway through

his first rite of passage.

He could live another 15 years,

making 30 more migrations.

The trip seems to be getting longer every year.

Over the past few decades,

the Leaf River herd's spring calving grounds

have gradually shifted 180 miles to the north.

Researchers believe we may be in the twilight

of this great migration.

They fear the Leaf River herd

will be extinct in just 65 years.

For now, even after clearing the river,

the herd still has a long way to go.

The treeline is still hundreds of miles away.

NARRATOR: It's late December on the bluffs

and beaches of California.

The male elephant seals

have been battling onshore for two weeks,

and now all the female northern elephant seals

have arrived.

The females bicker and bellow at one another

as they jostle for space on the beach,

but don't fight like the males do.

Females are pregnant when they arrive,

and give birth shortly after.

They lose 30% of their body weight

during their time on shore,

burning massive amounts of calories nursing

and protecting their pups.

Newborns weigh about 75 pounds.

The pups don't have any blubber, so their black coat

helps them soak up heat from the sun to stay warm.

Life on the bluffs is dangerous for the babies.

They're not alone.

Coyotes prowl, looking to pick off

weak or unattended pups.

Even the adult seals present a significant danger.

As males battle for control of the beach,

a pup that can't get out of the way fast enough

can be crushed.

Elephant seal mothers are fiercely protective

of their newborns.

A young male who comes too close

gets a stern warning.

She's not as big as the male,

but she will fight him if she has to.

The male won't take the hint.

Junior can't swim yet, so he can't flee.

He's trapped between the huge blubbery bodies.

The harem's dominant male comes to the rescue.

He sends the upstart male packing,

then drifts off back to sleep.

All elephant seals cover themselves

with sand while on shore.

It's likely an effort to keep cool in the hot sun.

They don't have any blubber in their armpits,

so raising one fin like this

is another way of cooling off.

They scratch constantly.

It probably just feels good,

but in a few months

it will help with the annual molt

in which the elephant seal

sheds huge swathes of skin.

After giving birth, there's just a short window of time

for the mothers to recover

before the mating season begins.

She nurses for just 28 days,

then immediately goes into heat,

signaling males of all ages

to try to mate with her.

The dominant male,

having fought off the competition,

begins the courtship

by placing a flipper across her back.

He uses his massive body to hold her in place.

Through a process called delayed implantation,

the pregnancy doesn't take hold for a few months,

so birth coincides with the haul-out next winter.

Not long after mating,

the mothers will leave the beach

to begin their long migration into the open Pacific

in February and March.

The pups are left behind for another six weeks or so.

They've got to fend for themselves,

and survive off the fat they've built up

until they learn to swim and hunt on their own.

The males leave soon after the females,

heading for the coastal waters off Washington State,

British Columbia and Alaska.

They'll all be back again, first for the spring molt,

then again in the autumn

to begin the cycle once again.

NARRATOR: By February, the days have grown longer

in the butterfly forests of Mexico and California.

The changing light draws the monarch

out of its hibernation-like state of diapause.

It's time for the butterfly to begin its migration north.

The butterflies vibrate their wings

to bring their bodies up to temperature

before beginning flight.

They have a long way to go.

The journey is up to 2,500 miles,

But unlike the trip south, the northbound journey

won't be completed by any one butterfly,

but rather will be an intergenerational relay.

The butterfly that came all the way from Nova Scotia

will die soon, but first, she will lay her eggs

on milkweed plants along the way.

Then her children will continue the voyage.

It takes four months, and at least three generations

to make the whole trip north.

Today, fewer butterflies make the migration

than in decades past.

In northern regions, suburban development

and herbicide use destroy milkweed habitats

where monarchs begin their lives.

In Mexico many forests are threatened by logging.

In California, government and private efforts are underway

to protect 450 overwintering sites

identified in the state

over the past 30 years.

Butterfly lovers hope to preserve

this flying animal empire

for generations to come.

NARRATOR: By land,

by air

and by sea

these creatures embark on life-threatening odysseys

to feed,

breed

and escape the changing seasons.

The world these animals move through

is changing all around them.

Some of these remarkable migrations

are on the verge of disappearing.

For now, they persevere,

following paths established

in a time before human memory.

The world's great

moving

moving animal empires.

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* THEME MUSIC