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Humanity is not alone in the urban jungles

we call home.

One species truly excels at living alongside us.

Loved by some and loathed by others,

they use an endless range of tricks and dodges

to seize opportunities in the heart of the city...

...where the truth about their lives

is full of secrets and surprises.

It's time to take a walk on the wild side

of London and New York...

to experience The Pigeon Hustle!

With a population more than 300 million strong,

you can find pigeons on every continent, except Antarctica.

They're a familiar part of the DNA of our great cities.

But there's nothing ordinary about pigeons.

They're one of the most remarkable birds on earth.

This is London -- Europe's biggest city.

Every day, thousands of commuters arrive here

at Blackfriars Bridge.

Few of them realize there's another city

beneath their feet...

...a pigeon city!

They may be familiar birds,

but each is an individual

with their own character and story to tell.

Meet Nelson, your typical young street pigeon.

He's been working the city for 2 months now

but he's yet to master many skills

you need to survive in this metropolis.

His life started deep inside this bridge.

Its cast-iron frame is full

of dozens of perfect pigeon apartments.

In one of these snug corners,

Nelson's parents are preparing for the arrival

of their next brood of chicks, known as squabs.

Both of them work to incubate the eggs,

keeping them at a constant 98.6 degrees.

The second egg was laid two days after the first,

but its chick will develop faster

as the second egg contains more protein in the yolk.

They both will hatch just a few hours apart.

Their cozy sanctuary is in sharp contrast

to the dangerous world outside.

A peregrine falcon!

Peregrines use the river to hunt.

Agile enough to snatch a pigeon

from beneath the arches of a bridge,

they can be on to you in seconds.

And they're not the only threat here.

Lesser black-backed gulls constantly patrol the arches.

Young birds are an easy target.

Many lives end here

on the shoreline beneath the bridge.

But not Nelson's.

Although the predators are dangerous,

pigeons have a range of superpowers

to help see them through.

If Nelson can use these effectively,

he just might survive the challenges of London life.

We associate pigeons with cities.

But it wasn't always that way.

Thousands of years ago, the ancestors of city pigeons

lived on sea cliffs and in caves.

There are still a few of their descendants left...

...known as rock doves.

You can find them on the wild coasts of Scotland,

living alongside the seabirds.

People and pigeons first became neighbors

around 60 thousand years ago,

when we shared the same caves.

Our ancestors domesticated them for food,

and we've been together ever since.

Venerated by ancient Egyptians...

...used to carry messages in wartime...

...and even studied by Charles Darwin

in his work on Natural Selection...

...there's never been a time

when pigeons weren't in the picture.

Over the centuries, people have selectively bred them, too,

into dozens of variations...

...which has given us the many varieties

of city pigeons we see today.

One of the most densely populated places in America,

the island of Manhattan, is home to 1.6 million people.

Its towering buildings are just like man-made sea cliffs.

So this is a great place for pigeon to flock.

And pigeons like to be close together.

Flocking helps them look out for predators,

stay warm,

and spot opportunities.

Manhattan is a pigeon paradise.

New York pigeons share a really close bond

with the human population.

Their ancestors arrived as the pets and companions

of generations of immigrants

who selectively bred them for racing and shows.

Over the years they escaped.

And now, their descendants are wild in the city.

Each neighborhood of Manhattan offers different opportunities

and is home to its own pigeon gang.

The gang you're born into governs where you go,

who you hang out with...

and above all, the special hustles you'll need to master.

On the edge of Central Park,

one gang has found a sneaky way of making a living.

It's here that the carriage horses are fed.

And the mixture of oats and grains

is similar to the diet of a wild rock dove.

The constant cooing of these pigeons is a sure sign

they're well fed.

So, there's always a full-throated chorus

from this sleek, healthy gang.

A few blocks downtown on 5th Avenue,

it's a very different story.

These pigeons have little access to any sort of green space.

They live a completely urban existence...

...surrounded by endless traffic,

noise, and pollution.

They're smaller, scruffier, and less well-nourished

than the central park flock.

But they've also found a way of making the city work for them.

This gang works to the clock.

The hot dog stand opens every day at 8:00 a.m. sharp.

And the pigeons gather bang on time for a free handout.

Feeding so close to traffic is dangerous.

And every day the 5th Avenue flock takes huge risks.

But pigeons have a set of remarkable adaptations

to deal with life in all this chaos.

With eyes on the sides of their heads they can see

an incredible 340 degrees around them.

And being a member of a gang helps, too.

With so many eyes, the flock covers each other's blind spots.

If a car gets too close, a real pigeon superpower kicks in...

...vertical take-off!

The birds bend their legs and launch skywards...

gaining enough height to prevent the downbeat of their wings

from striking the ground.

Their breasts are a solid pack of muscle

which helps generate enough lift for them to stay airborne.

A traffic-dodging pigeon goes from zero to 60

in just two seconds.

A true master of the street and air.

In London, young Nelson is looking

for his next opportunity.

Although captive birds can live to 30,

a city pigeon is lucky to survive for 5 years.

It's a tough life in the urban jungle.

Every day, Nelson has to eat between 10-- and 20%

of his body weight just to survive.

And seeking out all that food takes up most of his day.

But already,

he's beginning to get an idea

of what the streets have to offer...

...learning the best hustles...

and discovering where to hang out.

Pigeons have a great memory,

and Nelson is creating a mental map of London.

Soon he'll need to hit the streets again.

Nearby in Blackfriars Bridge,

one of the squabs has just hatched,

and the second isn't far behind.

Amazingly, pigeons feed their chicks on milk,

an ability they share with emperor penguins and flamingos.

High in fat, protein, and antibodies,

both adults secrete the milk from a gland in their throat.

They're the only animals in the world

where both parents can do this.

The milk is manufactured from just about anything

the pigeons eat,

so they're able to raise a family on a street diet

and breed at any time of the year.

Already the clock is ticking.

In just 32 days, the chicks will be out on their own.

Meanwhile, Nelson is heading out.

Pigeon gangs aren't democracies.

They have leaders who make the decisions.

Nelson just needs to follow...

for now.

This traffic island is a popular hang-out.

Some people have built a real bond with the birds here.

Pigeons have the ability to learn

and memorize human faces --

particularly ones that give them food.

Studies have shown that even if the person changes their clothes,

pigeons still recognize them.

Most of the birds here are well-fed locals.

As a rookie, Nelson is forced

to keep to the edge of the flock.

To get the best pickings,

he'll need to build up his bulk to help force his way

up the pecking order to the heart of the action.

In pigeon society, size really does matter.

Unlike Manhattan, with its single central park,

London is dotted with many greenspaces...

...which offer pigeons a range of refuges across the city.

In leafy Margravine Cemetery,

some enterprising birds have figured out

how to make a living by following

a fellow city-slicker...

...the gray squirrel.

Unlike pigeons, sharp-toothed squirrels

can crack open nutritious food like nuts.

So if you follow them around,

sooner or later, they might just drop a morsel or two.

But this leafy corner of London is also full of danger.

Charing Cross Hospital, which overlooks the cemetery,

is home to an active breeding pair of peregrines.

This year, they have 3 month-old chicks

already exercising their wings.

They're constantly hungry.

The parents need to catch at least three birds a day

to keep the family going.

So pigeons that choose to forage here are risking their lives.

They call it the city that never sleeps.

And pigeons have also embraced the 24-hour lifestyle

of the Big Apple.

In the heart of midtown Manhattan,

Times Square is a world of lights,

steel, and concrete.

On the face of it,

not much of a haven for wildlife.

Unless, of course, you're an urban specialist.

The pigeon gang here

has completely embraced this never-ending show

of sound and light.

Its well worth adapting your lifestyle

to capitalize on this "round-the-clock" food supply.

Scientists have discovered that the constant light

has altered the pigeons' body clocks...

giving them the ability to feed by day and night.

With the ceaseless light and noise,

getting any sleep at all here is a tall order.

But yet again, for pigeons, it's no problem.

Research has revealed that the birds

can actually cope for days on end

with minimal sleep.

Alongside this, they have the ability

to rest half of their brain at a time...

...which allows them to nap with one eye open.

Even in the noisiest, most chaotic place in New York,

pigeons need never miss a beat.

In London's Soho Square, it's lunchtime.

There's everything available here --

from Asian street food...

to fish and chips.

These processed carbohydrates and saturated fats

are a long way from a pigeon's natural diet.

But unlike other birds,

they have the ability to turn our junk food

into nutritious milk for their young.

Deep inside Blackfriars Bridge...

...the squabs are now two weeks old.

Their first flight feathers have started to appear,

but the yellow down remains.

Both parents are working simultaneously

to keep the squabs growing.

There are just two weeks to go

before they face the challenges of the city.

Although most pigeons stick to the routine

of following the local flock,

it's not uncommon for young birds to strike out alone.

Nelson has found his way to a London underground station.

It's time for him to go solo.

There's a lot to check out here.

It's well worth patrolling the platform.

This station is a terminus,

so trains sit stationery for a while.

Perhaps it's worth taking a chance

and checking inside for scraps.

Un-phased by the train heading off...

...Nelson works the train car.

Time to get off.

Finding his way back to the bridge will be no problem...

...as he can use a pigeons most famous superpower...

...navigation.

Homing pigeons can find their way home

from hundreds of miles away, in less than a day.

They have the ultimate built-in GPS.

How they do it is still not fully understood,

but we do know that pigeons navigate with the help

of the Earth's magnetic field...

...alongside an ability to find their way using landmarks

like buildings and roads.

Recent research has revealed that when they're close to home,

they use another sense for fine-tuning

their navigation -- smell!

The distinctive aromas of their neighborhood

literally guide the pigeons in,

once they're on their final flight path.

In New York City,

the temperatures are climbing...

...and so is the appetite for love.

It's time for pigeons to strut their stuff.

Pumped up and in prime condition,

a male pigeon is a sight to behold.

With an inflated throat...

the feathers on his neck shine with iridescent purple

and green -- colors generated by the structure of the feathers

rather than pigment.

In "pigeon-vision",

the show's even more intense

as the birds are able to see ultra-violet light.

Courtship is also accompanied by a special coo.

Generated from deep within the pigeon's body...

...their throats work like an amplifier.

Combined with distinctive bowing and strutting,

the cooing cacophony draws in potential mates...

while intimidating other males.

But the real sign that male and female

are ready to move on...

is the pigeon kiss.

This simulates the behavior used to feed baby pigeons...

...a skill these two will be needing soon.

After mating, the male needs to watch his back.

Others want to get in on the act.

So he escorts her as closely as he can,

keeping other males clear of his still fertile mate.

Pigeons usually mate for life,

and a pair will stick together through thick and thin.

Only death will end the relationship...

...at which point the surviving partner picks themselves up,

dusts themselves off, and starts all over again.

Pigeons don't usually mate until they're a year old.

Nelson still has all of this ahead of him.

But other city families are much further along.

On Charing Cross Hospital,

the peregrine chicks are close to fledging.

For the local pigeon population, it's time to go on red alert.

With three hungry chicks now ready to fly,

the falcons must catch a substantial amount of food.

So pigeons need to be very wary.

Chicks need to learn to kill live prey,

so the parents bring back some unfortunate pigeons, alive.

But this chick's too slow.

In level flight, a pigeon can actually outpace a peregrine.

So this time, the escapee lives to fly another day.

Three miles east,

Nelson is exploring central London's biggest green space...

...Hyde Park.

Generations of Londoners have come here to feed the birds.

It may seem peaceful,

but there's danger at the water's edge.

While most pigeon eyes are trained on tasty treats...

...one pair of eyes is fixed on them.

Hunched down like a leopard,

this gull has developed a surprising skill.

With his experience of the gulls at the bridge,

Nelson knows the value of keeping his distance.

But there are some newly emerged squabs here,

and they have no idea of the killer

that stalks the edge of the flock.

Time for Nelson to move on.

There are better opportunities to be had

in the city's West end.

Operating in this environment

will require Nelson to draw on everything

he's learned about surviving in the busiest parts of London.

Pigeon intelligence may be very different to ours,

but their ability to recall thousands

of images and situations

makes them one of the sharpest birds on the planet.

Their brains may not be large,

but they're more densely packed with neurons

than those of other animals of similar size.

Dodging the West End crowds is one thing,

but the mission of every city pigeon

is to find the way to food, fast.

And being able to decode their environment is a critical skill.

Experiments using rewards placed in pots with colored lids

have shown that pigeons quickly learn

to associate different colors with food.

They're so efficient at doing this,

that scientists are using analysis

of the machine-like precision of a pigeon's brain

to refine artificial intelligence systems.

The heart of London's West End is full of patterns,

signs, and symbols.

And Nelson knows that some of them mean food.

A pigeon can distinguish combinations

of patterns and symbols, too.

That means that they're even able to separate the work

of different artists.

In a 1995 study,

scientists trained them to distinguish the works

of Picasso and Monet based on artistic style...

...something beyond even the cognitive skills

of young children.

At three months old, Nelson is still growing up.

He's undergoing his post juvenile molt,

and it's really important to keep his feathers

in tip top condition.

He's learned that fountains offer the best place for a bath.

Back inside Blackfriars Bridge,

the squabs have completely transformed.

They're now a month old

and almost ready to start their lives in the city.

Just a few strands of yellow down

will be a clue to their novice status.

The next stage of a city pigeon's journey

is the most precarious of all.

Squabs get very little help when they leave the nest.

Once the chick emerges, it's pretty well out on its own.

In New York, near the Brooklyn Bridge,

another youngster is facing these challenges

for the first time.

He's fledging a little early.

Not all his feathers are fully grown,

and he has little insulation,

but it's still summer,

and that'll give him a fighting chance.

He finally plucks up the courage to join the flock.

This gang, which controls the territory

around the subway station,

is a hard-bitten bunch.

The squab will need to feed soon

if he's to gain enough fat to keep warm and thrive.

Less than half of all squabs

make it through their first month.

And failure to compete for food is the main cause of mortality.

He's definitely the bottom of the pecking order.

And the other gang members are merciless.

No parent will come to feed him now.

His pigeon instincts are kicking in.

Few squabs survive their first year,

but if he can make this milestone,

his chances will climb as he joins the breeding population.

He'll need to build resilience, fast, as being a street pigeon

has never been tougher.

For a bird that was once revered and celebrated so much,

life is now full of extra challenges.

London's Trafalgar Square once teamed with pigeons.

In the 1950's and '60s, thousands made their home here.

They were a tourist attraction in their own right,

and inspired by Mary Poppins,

visitors were even sold pots of pigeon food.

But pigeon droppings are acidic and can corrode stone,

brick, and metal.

By the early years of the 21st century,

the attitude towards pigeons began to change.

Our former friends and allies had become pariahs.

The war on pigeons had begun.

A complete ban on pigeon feeding was implemented here.

And new, feathered allies

were enlisted to keep the pigeons away.

Harris hawks now patrol the square.

They may not have the pace of a peregrine...

but a daily tour of the area is enough to deter most pigeons.

The square that once heaved with birds is now almost pigeon free.

However, you can't keep a good pigeon down for long.

If you work on keeping them out of one place,

they'll always find an opportunity somewhere else.

They're ingenious

and can get into the most surprising places.

Back in New York,

the Brooklyn gang have worked out

that some of the best feeding places are deep underground.

Pigeons are so maneuverable

that they can navigate the stairs and escalators...

...to exploit the many opportunities

beneath the streets!

No other bird would do this.

Perhaps it's their ability to adapt quickly

to our changing world that makes pigeons so successful.

Wherever we go, and however we choose to make a living,

pigeons are never far behind...

finding new places to live and feed.

In London, Nelson is also learning to push the boundaries.

River Boats carry passengers

up and down the Thames all day long.

and if you're brave enough to hop on board,

there are plenty of scraps and crumbs to scavenge.

Good morning, everybody.

Bolder pigeons like Nelson are even happy to take a ride

while the tourists admire the sights.

This hustle also suits less mobile pigeons.

One of the few wild animals that can live with a disability,

these birds still make a living, even with missing toes and feet.

Nelson is really making the grade as a city pigeon.

He's learned to make the best of the countless opportunities

on the Streets of London.

Like millions of others around the world,

he's learning the rules of ducking, diving,

and surviving here in the city.

Pigeons are smart...

...resilient...

...surprising...

and inspiring.

They live out their lives alongside us,

adapting to our changing ways,

and working out ingenious hustles to find food

and avoid danger.

Our world is theirs, too,

and they deserve our respect and admiration.

And let's face it, for many people living on this planet,

a pigeon is the closest you'll ever get to a wild animal.

Long may they thrive...

here in the heart of the city.