Original subtitles

NARRATOR: In the shadows of London, England,

one of the world most successful species,

the brown rat, stakes its claim.

A continent away,

the sea lions of San Francisco's Pier 39

take a different tack,

hauling out en masse

in the light of day.

And just outside Melbourne, Australia,

fruit bats forced from their native home,

take to the trees of a city park.

In search of food and shelter,

these uninvited guests

use sheer numbers to secure new territory.

Their very survival

may depend on infesting a place

where they're not welcome.

NARRATOR: Inside the different realms

of the wild kingdom,

Members of a single species

assemble in droves.

And one flock,

herd,

or troop

reigns supreme.

These are the world's great

These are the world's great

NARRATOR: England is the most overcrowded

major country in Europe.

On average, over 1,000 people

are squeezed into every square mile.

That's over 50 million residents.

And some say,

there are just as many rats.

On the outskirts of London,

a derelict basement has been overrun

with brown rats.

A group of rats is called a mischief.

It's a fitting term.

At least 100 of these large rodents

wreak havoc in the shadows of this building.

It's a full-blown infestation.

It was once believed that there was one rat

for every person in the UK.

Scientists suggest that it's more likely

one for every six people,

but that would still mean

some 10 million rats.

With the exception of Alberta, Canada,

where extermination efforts

have kept the province rat-free since the 1950s,

rats live everywhere people do.

After humans, this is the most successful mammal

on the planet.

Which makes it one of the world's

greatest animal empires.

The brown rat is also referred to

as the Norway rat.

British naturalists of the 18th century

thought that it had migrated to England from Norway.

But the species, in fact,

originated on the plains of Asia

in Northern China, and Mongolia.

Some time in the middle ages,

they began boarding ships,

traveling far and wide,

and spread to the four corners

of the globe.

By that time, black rats had already spread

to Europe during the Roman Empire

and had firmly cemented their reputation

as household pests.

But the larger, more aggressive brown rats

eventually took over,

displacing their relatives.

Brown rats eat a wider variety of food.

The transition from wooden buildings

to brick and tile construction

also favored brown rats.

They're much better diggers

and can tunnel under walls,

and left black rats out in the cold.

They also have very good hearing,

a highly developed sense of smell,

and can see ultraviolet lights

that most animals cannot.

But while there's much to admire

about this super species,

a rat is a very unwelcome guest.

It was long believed that rats

were responsible for the Black Death

that devastated Europe in the 1300s.

Evidence now suggests they may have been falsely accused.

However, the stigma remains.

Rats are known to transmit diseases,

and they make a mess of basements and attics.

So as these rodents multiply,

so too do efforts to exterminate them.

They are under near constant threat.

Rats don't live long. The maximum life span

of a brown rat is around three years.

Most barely manage one.

So for this animal empire,

every day is truly a rat race.

On the northern coast of California,

the city of San Francisco

is known for its historic icons

like the Golden Gate Bridge

and Alcatraz Prison.

These landmarks,

along with the region's moderate climate

and easy-going pace,

make it a popular place to live and visit.

But it's not just an attractive place

for residents and tourists.

Pier 39, once a popular mooring spot

on San Francisco Bay,

is now infested with sea lions.

Sea lions are part of a group

known as "Pinnipeds",

commonly known as seals.

In fact, the clich�d circus seal,

balancing a ball on its nose

and jumping through hoops,

is typically a California sea lion.

Sea lions join fur seals

to make up the family "Otariidae",

also known as eared seals.

Unlike other seals, they have external ear flaps.

In addition, you can tell the difference

by the sea lions' proportionately larger

fore-flippers and pectoral muscles.

Sea lions also have a long thin ridge of bone

running along the skull,

known as a sagittal crest.

The range of the California sea lion

stretches from Alaska in the north,

to the Baja Peninsula, of Mexico

in the south.

California sea lions spend the summers

breeding on the Channel Islands,

just over 350 miles

south of San Francisco.

Once the breeding season is over,

females stay close to the newborns on the islands.

The males set out to the open ocean in search of food

for as long as two weeks at a time.

Between fishing trips, they need to rest,

or "haul up" on shore.

Many do so on the beaches

of northern California.

Large colonies are a fairly common sight

along the coast,

but less expected in the throng

of a bustling metropolis.

Pier 39 is in the heart of the city.

It's smack dab in the middle

of San Francisco's busy waterfront,

sandwiched between restaurants,

shops, and other attractions.

Since 1989,

sea lions have taken over

Pier 39's K-Dock.

The exact reason is unknown.

It may be that it's simply a convenient rest stop

between the breeding grounds to the south,

and the foraging waters to the north.

Whatever the reason,

the arrival of these boisterous bulls

has become a seasonal event each winter.

Their presence shuts down the pier

to boat traffic.

And this hauling out has become

an inner city infestation.

an inner city infestation.

Across the Pacific,

on the south coast of Australia,

the city of Geelong

is an hour's drive southwest of Melbourne.

Located on the waters of Port Phillips,

Geelong is considered

the gateway city for the region.

And it is rapidly growing.

Home to more than 180,000 people.

This Melbourne suburb has been called

one of Australia's most livable cities.

And not just for humans.

Geelong is also home

to tens of thousands of bats!

The grey-headed flying fox

comes by its name honestly.

It looks a lot like its namesake.

But it is indeed a bat.

And a big bat at that.

The largest in Australia

and one of the largest in the world.

Bats are mammals,

the only mammal capable of sustained flight.

Bats belong to the order "Chiroptera",

which literally means "hand-wing."

There are two sub-orders.

Most are familiar with the "micro bats",

popularized by Halloween haunted houses,

horror stories and the legend of Dracula

Micro bats are smaller,

only about the size of a mouse.

They live in caves, and eat bugs.

They also use "echolocation" to find their prey,

calling out and using the echo

that bounces back to navigate.

The grey-headed flying fox, on the other hand,

is a mega bat.

It's not only larger, but it also has good eyesight

and a superior sense of smell.

This is their food of choice, fruit.

In fact, they're commonly known as fruit bats.

And instead of caves, they live in trees.

Today, fruit bats only live in the tropical rainforests

of eastern Australia.

Decades ago, they were endemic

to all southeastern Australia's forests.

Numbers were in the millions.

But as trees were cut down

to make way for expanding cities and towns,

factories and farms,

development put added stress on fruit bat habitat.

It is estimated that as much as 70%

of some of the flying foxes' favored foraging sites

have been lost since European settlement.

As a result, there are now only between

three and six hundred thousand in the range.

They've simply run out of places to live.

So in the late 1980s, the surviving fruit bats

in the southeastern state of Victoria,

made a move.

They went from the wild woods,

to Melbourne, and other nearby cities.

Now, at least three permanent colonies

make their home here,

including this site, in Geelong's Eastern Park.

It's hard to blame them.

There's food and water nearby.

It's warm in winter,

and cool in summer.

And the city's green spaces, like Eastern Park,

offer protected trees that are ideal for roosting.

As their forest homes continue to fall,

more and more fruit bats

move to the city looking for a roost.

The Eastern Park colony

has swelled to as many as 30,000.

These big bats are not necessarily

a welcome addition to the city.

They can be intimidating and noisy.

They damage other vegetation,

and they are known to carry dangerous viruses.

What was once an occasional stopover in the city

has become an infestation.

Bats in the belfry are one thing;

bats on the golf course

is something else altogether.

But for the flying foxes themselves,

the stakes are even higher.

Their very survival

depends on a peaceful coexistence

with their human hosts.

Great Britain's rat population

doesn't have quite the same housing problem

as the fruit bats.

While Australia's bat-friendly forests are scarce,

Britain offers more than enough

suitable habitats for rats.

There are plenty of sewers, garbage-filled alleyways,

and bleak building basements to choose from.

Rats will live pretty much anywhere

they can find food.

And they'll eat just about anything.

Rats are true omnivores.

They prefer grains and meat,

but studies have shown that rats aren't picky.

Scrambled eggs, macaroni and cheese,

pet food, and even leftover fruit.

They'll eat whatever happens to be around.

Once rats identify a source of food,

they first need to gain access.

It doesn't take much to make an entrance.

With a collapsible rib cage that's hinged at the spine,

they can squeeze through cracks half their size.

If a rat can get its head through a hole,

the rest will follow.

They can also enter through plumbing pipes,

either by using their razor sharp claws

and excellent balance to climb up the outside.

Or they use their superior swimming skills

on the inside.

They are such good swimmers

they can tread water for hours on end.

And yes, they can even enter a building

through a toilet.

Once inside, rats start making their home

by burrowing.

In some cases, this means digging underground

and making tunnels.

In others, they collect nesting materials,

insulation, straw, and any lightweight material

they can use to create an enclosure.

Burrows provide the pack

with shelter and food storage,

as well as safe, thermo-regulated nests.

Each burrow has its own nest chamber.

But rats may also share a burrow

and raise their young together

in a "communal nest".

They connect their burrow to others

made by their relatives.

It's a system of one to six little burrows,

not unlike families that chose to live

in the same village.

After a few days,

a second entrance, called a bolt-hole,

is added by digging from below.

It serves as an emergency exit

in case the burrow is invaded.

Once the first burrow is finished,

rats will continue to add on,

using the same pattern,

dig a tunnel, empty out a cavity,

add a bolt-hole.

Outside the burrow,

brown rats tend to confine their movement

to the same routes every day.

Gradually, trails form on the surface.

Rats don't like to go far.

As long as food is available,

they'll stay within 65 feet

of their nest.

It's a matter of avoiding risks.

Even though these are incredibly adaptable creatures,

they're also very vulnerable,

especially outside the burrow.

Predators, interspecies conflict,

and the occasional run-in with an exterminator,

can result in a rat colony

having a mortality rate of 95%.

Most rats don't make it past their first birthday.

How is it then, that rats have maintained

such a successful empire?

In a word,

In a word, breeding.

Rats reach sexual maturity at an early age,

at just five weeks old,

and usually start breeding at two months.

They can breed throughout the year.

Mating behavior depends on the colony's

population density.

When numbers are low,

one male rat will monopolize a burrow of females.

It's a polygynous system

where he mates with a number of females in his group,

and only the members of his group.

In this case, the male will defend his territory

fiercely from other rats.

He'll chase, bite and box,

fluff up his hair, hiss, squeal,

and wag his tail,

anything to keep other males

away from the females in the burrow.

At higher population densities,

males can no longer defend

a burrow against rivals.

There are simply too many.

One alpha male rules the pack,

but he can't control all the females.

In this polygyandrous system,

multiple males mate

with multiple females.

A female rat goes into heat, or estrus,

every 4-5 days.

The gestation period is only 21 days.

Which means she can have about

a dozen litters in one year.

And each of those litters can have

anywhere between 7 and 14 pups.

Her offspring will start breeding within two months.

And their offspring

will be able to breed in another two months.

That means, one mating couple

can produce as many as 15,000 descendants

in a year, if left to breed unchecked.

At this rate, a few rats can quickly become

an infestation.

And an infestation can spell trouble.

A crowded rat pack leads to

increased competition and conflict.

And can draw the unwanted attention

of the local exterminator.

Like rats and bats,

California sea lions are motivated by hunger.

The pod at San Francisco's Pier 39

has figured out something

their fellow migratory sea lions haven't,

that the safe harbor of the pier

provides them with just about everything they need.

For one thing, there's plenty of fish in the sea.

Or in this case, herring in the bay.

Sea lions are binge feeders,

eating all they can when food is plentiful.

They'll eat anywhere between 10 to 40 pounds

of food or more every day.

In addition to the herring,

they'll prey on some 50 species of marine life,

including squids, octopuses,

hake, salmon, and anchovy.

They are excellent swimmers

and can spend 15 hours at sea,

diving up to 200 times.

They hold their breath for up to 20 minutes

and dive to depths of 1,000 feet.

And they are speedy swimmers,

clocking in at 22 miles per hour.

While the Pier 39 sea lions

may not have to work so hard for a meal,

they still need a spot to haul out and rest.

And the Pier provides a perfect accommodation.

The docks rise and lower in the tide,

saving them from having to move up and down

from rocks on the shore.

It's not unusual for them to sleep 8 to 12 hours a day.

And they fast for several days at a time.

Sea lions are very gregarious, social animals,

so it's normal for large groups to haul out together.

California sea lions can't sweat or pant.

Their normal body temperature

is about 100 degrees Fahrenheit.

In order to regulate this temperature,

they must move around in their environment.

When it's cold,

a sea lion will cozy up to others to stay warm.

If it gets too hot,

he'll lift a flipper or fan himself.

Sea lion flippers have many capillaries

that can be cooled off by the wind

when sunbathing.

Of course, he can also take a dip in the bay.

The Pier also is also a place to haul out,

providing protection, both from storms and predators,

like sharks and orcas.

It may seem like an ideal spot

for these pinnipeds.

But that means it's a popular one, too.

On average, there can be up to 600

hauled up on the pier.

A record 1,700

were counted in 2009.

And there's not much room

for a few hundred sea lions.

These are massive marine mammals.

A fully-grown male

averages more than 660 pounds

and is about eight feet long.

This is a boisterous bunch,

prone to bickering.

When it comes to prime real estate,

sea lions aren't afraid

to fight over who got there first,

and more importantly, who gets to stay.

and more importantly, who gets to stay.

Outside the city of Melbourne, Australia,

a colony of grey-headed flying foxes

has taken over the trees

of Geelong's Eastern Park.

These fruit bats have both summer

and winter roosting camps in the trees.

This summer camp,

from September through round June,

is their main camp.

During the day, hundreds hang from the branches

high up in the trees.

There's a good reason they hang upside down.

Bats are top heavy.

The biggest bones and muscles

are those used for flying.

It's far more energy efficient to hang

than to defy gravity and stand upright.

It's during these long summer days

that they mate.

Males set up mating territories,

generally three-and-a-half body-lengths along branches.

Males fight for these territories.

Those with the best locations, closer to the center,

have access to more, and better, females.

Males with lower-rent spots

may have only one mate,

or they're stuck being bachelors.

At the beginning of the mating season,

adult females move in towards the male territories

where they become part of 'harems'.

The harems consist of a male and up to five females,

who come and go.

It's the females who control the copulation process.

Mating takes place during the day

between March and May.

After about six and a half months,

babies, known as pups, are born.

For the first three weeks,

the pups are heavily dependent on their moms.

Bat mothers provide milk and warmth for their babies,

which cling to their moms for the first few weeks of life.

As the day comes to a close,

the adult bats ready to leave in search of food.

Pups that are not yet three weeks old

will cling to their mothers when they go foraging.

Older pups remain in the roost

until they are weaned at about six months.

Bachelors and lactating females

leave the roost first.

Mating males wait and guard their harem

until all have left.

It's a catch-22.

Those that leave earlier,

have more time and light to work with.

But this also makes them more vulnerable

to predators, like hawks and eagles.

For each fruit bat, it's a decision

that could very well determine

whether they will survive the night.

In the dark recesses of this London basement,

there's tension in the rat colony.

There may have been plenty of space

when the infestation began.

But now, the rapidly expanding population

is putting pressure on the over-crowded burrow.

There's just not enough room.

And now there are even more mouths to feed.

Even though most rats

won't live past the age of two or three,

they're reproducing far faster than they're dying off.

In just four months,

this colony has grown by a factor of ten.

Conflict is inevitable.

Crowded rats turn aggressive.

The alpha male goes on the offensive;

he attacks and pushes out lower ranking males.

It may seem like an extreme solution

to the overcrowding problem,

but it's a matter of maintaining the balance.

If it gets too crowded,

the strong will drive weaker members

out of the colony.

If the population declines,

the remaining rats simply increase

their reproductive rate to restore numbers.

But it's not always one big rat race

to see who stays and who goes.

Studies have shown that rats

also have the capacity to work together.

They'll cooperate to get food.

It's even suggested that a rat

that has received help in the past

is more likely to help another rat,

even one that is unknown to him.

In other words,

cooperative rats don't just return favors,

they also 'pay it forward.'

Scientists call this "general reciprocation".

It's the first time this behavior

has been documented in nonhumans.

And another example of how intelligent

and adaptable these rodents are.

And they must be.

Though rats have the respect of researchers,

and some even find a happy home as pets,

they generally remain unwelcome house guests.

Rats are under constant threat.

And so, as the day breaks,

the mischief settles safely

back into the burrow.

They spend the daylight hours

hidden away as best they can.

For some, there's work to be done storing food

and maintaining the burrow.

For others, it's time to sleep.

They huddle together to conserve heat.

New pups nestle together, depending on each other,

and the heat from their mother.

Once the young males are old enough,

they will leave the nest and strike out on their own,

setting off in search of new territory,

and once again beginning the cycle of infestation,

and expanding the empire.

It's October in the city of San Francisco.

There's no vacancy on Pier 39's K-Dock.

At its busiest, the pier may be home

for 500-600 sea lions.

It can get awfully noisy when a few hundred

large marine mammals haul out of the water.

California sea lions

are among the most vocal of all mammals.

(sea lions bark)

They bark, growl, and grunt loudly.

(sea lions growl)

(sea lions bark)

During the mating season,

males will bark incessantly at each other

as they clash over territory.

These fights frequently turn physical.

Breeding bulls will do whatever it takes

to establish dominance and claim a harem.

Here on Pier 39,

during the non-breeding season,

it's the young submissive males

that are most aggressive.

Bulls usually reach

10 years of age before they mate.

When that time comes,

they must be ready,

so they train.

It's every sea lion for himself.

(sea lions growl and bark)

While some scuffles at the pier

are over favored spots on the docks,

most fights are between these juvenile males,

practicing the skills that they will need in the future.

(sea lions bark and growl)

They work their way up the hierarchy,

taking part in regular bouts

as they try to climb the social ladder.

Only the strongest will get the chance to mate.

(sea lions bark and growl)

It's a rowdy affair.

(sea lions bark and growl)

They grapple and bite each other,

and bump and thump their necks and chests.

(sea lions bark and growl)

Though injuries are common, fatalities are rare.

(sea lions bark)

A skirmish usually ends when one or the other

is physically pushed away.

Currently, the population of California sea lions is healthy.

But it's not without its threats.

Foraging adults can become entangled in fishing nets

or plastic packaging materials,

causing injury or even drowning.

And the planet's changing climate is a growing concern.

Declines in sea lion numbers

have been linked to exceptionally warm currents

that cause fish populations to shift.

This can lead to poor nutrition,

especially dangerous to pregnant and nursing females.

These are increasing threats

to the survival of the species.

These young bulls face an uncertain future

in a changing world.

When the summer is over,

they will join the other adults as they make their way

from Pier 39, back to the breeding grounds

off the Channel Islands.

On the islands, their training will be put to the test.

These young bulls will fight to win breeding rights,

the chance to continue their lineage,

and ensure a future for their empire.

and ensure a future for their empire.

Bat's wing bones are the same as those

of a human arm and hand.

But these bones are proportionately much longer.

They're connected by a double membrane of skin

that forms the wing.

Different bat species have different wing shapes

depending on where and how they eat.

Flying foxes have an average wingspan

of three feet.

Flying foxes need their large wings

to travel the relatively long distances

to fruit-filled forests and fields.

As day turns to dusk,

the sky above Geelong's Eastern Park

comes alive.

The grey-headed flying foxes

are setting off in search of food.

When a wave of these large bats take flight,

it quickly fills the sky.

Their departure is an impressive sight.

Most will travel an average radius

of about 20 miles from the roost.

Some will even go as far as 60 miles to find food.

They travel at a speed of about 23 feet per second.

If conditions are right,

they can ride the wind and travel twice as fast.

And they have to hurry

if they're to be back before sun up.

It's a myth that bats are blind.

All bats can see,

and see better than humans at night.

But fruit bats have the best eyesight of all.

They use their big eyes,

along with a keen sense of smell,

to locate food.

Many of their food plants have blossoms

that bats can see from above.

They're on the lookout for the flowers of native trees,

such as the many species of eucalyptus,

as well as turpentines, and paperbarks.

And of course, fruit.

Bananas, mangos,

dates, avocados,

just about any kind of fruit will do.

Far from the safety of the roost,

these flying mammals are vulnerable.

Out in the open air,

predatory birds like hawks and eagles

hunt the night sky.

Weasels, snakes, and even cats

prey upon fruit bats when they stop to rest or eat.

But it's humans that present the greatest danger.

Fruit farms are an attractive place

for a grey headed flying fox to find a meal.

Farmers have been known to trap and shoot bats

to protect their crops

Recent conservation efforts

are trying to curb this trend.

It's part of an increasing awareness

of the important role that fruit bats play

in the local ecosystem.

The seeds they swallow

move quickly through their system.

They take only 20 minutes to digest,

and are spread through the fruit bats' excretion.

Bat guano is good for the environment.

Increased clearing in the last two centuries

has isolated scattered patches of forest.

Flying foxes are able to move seeds

over longer distances than insects and birds,

linking these patches of native vegetation.

In this way, grey-headed flying foxes

can help rebuild the habitat

that has been taken from them.

But for now, as day breaks,

they must return to the safety of the roost,

to the Eastern Park trees

and the city they have claimed as their home.

NARRATOR: From the basements of Britain,

to bustling San Francisco Bay,

to the cities of southern Australia,

every member of the wild kingdom

depends on finding a suitable home.

For rats, sea lions, and flying foxes,

that means moving in where they may not be welcome.

But whether invited or not,

these species are simply struggling to survive,

using strength in numbers

to claim new territory

and continue the legacy

of their

of their animal empires.

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