Winter in the suburbs of London.
It's late. People are tucked up,
or watching David Attenborough on the telly.
'And the vast herds follow.
'Wildebeest are free to travel
'wherever the quest for food leads them
'and they home in on the scent of wet soil
'that carries the promise of fresh grass.'
There's a migration going on here, too.
The last bus does its rounds
and the old residents of this place are looking to reclaim the streets.
Fallow deer are stepping into a world
where nothing is quite natural.
Above them, this leaf should have fallen months ago,
but a tiny patch remains, confused by the streetlights
into believing winter has not yet arrived.
On the ground, the council's lawnmowers encourage fresh grasses
tastier than the brambles in the woods.
Like the wildebeest herds in Africa,
the deer of Essex are attracted to their own suburban Serengeti.
There are not lions here,
but cars can kill, too.
They won't be deterred - the manicured lawns are irresistible.
Finally they can eat their fill.
By rush hour, they'll be long gone.
And it's not just deer.
There are other mass migrations and alien invasions,
a world most of us never see.
There are a lucky few
who have opened their eyes to this wild subculture.
Is that one feeding now?
For them, London is a magical wilderness full of opportunity.
Every building in London resembles a cliff face.
Good dog.
No, there are no foxes in the countryside now.
They're all in London.
They'll come right over like helicopters.
We're surrounded. This is the real urban jungle.
It's like a gang here and a gang there, and it's all about territory.
I think she's camera shy.
Our window on to this world is through some unlikely heroes.
This is the natural history of London
as you have never seen it before.
'This train is ready to depart.'
To understand the nature of London,
we need to look at it as we would look at any other habitat.
But there is no habitat on Earth that evolves as quickly as a city.
London's wildlife has had to adapt
to this extreme eruption of rock and glass.
Down in the streets,
spring reveals the city is still throbbing to the seasons.
Trees, the giants of the old order,
now reach up between towers and wheels,
living signposts to the arrival of summer.
Despite all the changes,
London is still a handful of gently rolling hills
that fall away to a flood plain of drained marshes...
with a river running through it.
Before we tried to contain it,
the Thames reached over five times its current width.
Fighting back this tide is an ongoing battle.
You can never keep nature out -
it will always seep back, bringing its magic with it.
One recent arrival swam in through the lock gates of Canary Wharf
to an old coal dock that separates the towers of industry
from Billingsgate Fish Market.
The Billingsgate Porters are a London tradition.
For 500 years, men have risen at 4am each day
to distribute fish to a hungry city.
But these tradesmen have gone soft on an animal
most fishermen would see as the enemy.
I think she's camera shy.
When I first saw her, it was dark
and right down the other end of the docks there
and I was coming down the stairs from the changing room,
and I saw this shape in the water and I thought it was a man in the water.
No, I didn't think it was human. I could see it was a seal.
I'm not that naive, you know?
Just kick this. Like that...
METAL CLANGS
And up she comes.
Like Flipper.
This seal can escape to the Thames should she choose to do so,
yet she prefers to stay.
Certainly, catching fish here is a lot easier.
She's a bit fussy - she won't eat plaice or nothing like that.
She'll eat mackerel, herrings - soft fish, like, you know?
What she likes the most are the squid
because they're nice and soft, I suppose easy to swallow.
Salmon, I reckon. Salmon and trout.
Nice, big, juicy mackerel for her.
Bit hungry. Looks a bit narrow.
METAL CLANGS
She just puts it in her flippers and claws and just strips it down.
Strips it right off.
It's an unlikely relationship.
Men considered to be tough as old nails
raiding their stock for the love of a seal.
She'll sort of go up and down, follow you along.
She sort of performs, you know? Especially when she's hungry.
There's a good girl. A lovely girl.
There's more fish in there than there is in there!
For those of us who care to look, London is full of surprises.
You've had whales up the river, in't ya?
Had whales, dolphins.
Terns - red Arctic terns round here.
You see more in London and surrounding areas than what you can in the countryside.
It's all around you,
if you only look and see for yourself what's about.
Some people walk about with their head in the clouds. They don't look at nothing.
Like I say, my garden - toads, slowworms, frogs.
Middle of London, you know?
I mean, we'd never see a slowworm when we was kids.
Grass snakes. You know, all coming in. Where are they coming from?
See, what you don't see a lot of now - hedgehogs.
When I first moved in the house where I am
it was heaving with hedgehogs. You know, there was too many of them.
The habitat of London is not for the faint hearted
and hedgehogs have it tougher than most.
They don't understand roads and they confuse a pile of cuttings
as a place to doss down for the night when it's actually a bonfire.
They have even developed a habit for the sweet nectar of coffee
at the bottom of a Styrofoam cup.
If it gets stuck, it can be fatal.
They may not be streetwise yet,
but they muddle along where they can.
Others have adapted brilliantly
and left their country cousins far behind.
To the feral pigeon, the streets of London are paved with gold.
Most Londoners barely give these birds a second thought,
but Lisa, far from ignoring the humble pigeon...
- Stay, boys. - ..has developed an obsession with them.
It's all in the art of stealth.
She's not a scientist - she's just a girl with an unlikely passion.
But you don't crawl around the streets of London for six years
without picking up a thing or two.
We are in the middle of Soho,
so all these guys basically live in Soho Square.
Scientists believe that pigeons used to navigate their way
using the Earth's magnetic field
and there are actually a lot of scientists now
that believe they just use roads like everybody else.
So literally, you know,
a Manchester pigeon might arrive in London by flying down the M1.
See the bobbing heads?
Because they've got an eye on each side of their head,
they balance it up by bobbing their heads,
which actually gives them amazing eyesight.
They've also got a beak that works like a straw.
When most birds drink, they take a sip and knock it back.
Pigeons can literally suck up water as if their beak is like a straw,
so it means they can literally get a good old pint-full very quickly.
Lisa tracks them all over London, and she thinks their characters
are defined by the neighbourhood they come from.
God - easily spooked, these pigeons of Peckham.
I've now filmed pigeons or shot pigeons
in almost every borough in London pretty much.
Kensington, obviously, they tend to be
feeding largely off smoked salmon and caviar.
A whole different kind of posher type of pigeon, really.
And obviously this is the extreme, which is south of the river.
The minute you go south, they're quite different.
Just slightly more edgy, basically.
Slightly more edgy, a little bit more of a gang mentality.
They're a slightly scarier pigeon down here.
She has an online diary about a pigeon called Brian
and with thousands of hits on his website,
he's fast becoming a London celebrity.
There's Brian. That's Brian Pigeon -
see that light grey one there, with the black stripes around him?
That's how you always know that's Brian Pigeon.
The online diary is what he gets up to every day,
hanging out with mates, disappearing with mates.
Doing his own thing, partying.
He organised a protest flyby
that happened to coincide with the G20 protests
and, literally, I came down here to cover it
and there were thousands of pigeons. Thousands from all over the country,
so he'd managed to get this whole thousands of pigeons together
and then they did a mass flyby.
Did a huge flyby over to the mayor's office, flew round it
and then flew all the way back again.
Lisa's blog may not be science, but it's not all flight of fancy.
# Don't got a lot of time
# Don't give a damn
# Don't tell me what to do
# I am the man. #
The descriptions of Brian's love-life all over London
taps into one of the keys to the pigeons' success.
# God, shine your light down here
# Shine on the love
# Love of the loveless
# Love of the loveless. #
If you just care to look, you will see pigeon courtship
going on all over the place and all year round.
But the girls aren't easy.
Yeah, normally he will give it a couple of goes first,
with most of the ladies running away.
But finally, when he meets one who's up for it
and a little bit of eye contact,
a little bit of the puffing of the chest.
And then the turning round in circles, and I've often thought
it's just a, kind of, "Look - here's me from all sides."
When they do finally manage, though - he's done the puffy chest bit,
he's done the dancing round in circles bit and she's gone, "Yeah, all right, then. I'm up for it."
Yeah, then there can be all sorts of lovely entwining of necks,
pecking each other's beaks,
feeding each other bits of spit, which is nice.
And, yeah, then finally, up he jumps, has a little wiggle around.
But, of course, they don't actually have penises.
They're not actually well hung or anything like that. They actually do have a little hole.
Well, I think that's generally why the female's a bit like,
"I'm really sorry - I'm not in the mood.
"It's all going to be over and done with in about ten seconds.
"And frankly it hurts my back."
The male tends to bask in the wonderful afterglow,
the female's going, "Oh, my back.
"He was a little bit heavy, that one."
But the male's all kind of like,
"Yeah, look at me. Check out me and my packet."
Six weeks later, loads of eggs.
The pigeons hide their nests
on the rocky crags and cliff faces of our buildings.
If you think about it, you never see a baby pigeon.
Like many London teenagers,
they stay with their parents until they are fully grown.
They'll only come down when they look just like an adult.
Once fledged, the pigeon is free to fly the canyons of London
to places none of us can go.
But up here, a predator's moved into the neighbourhood
and it's the fastest animal on the planet.
During the Second World War,
Parliament ordered all Peregrine to be killed
because they could hunt the carrier pigeons
bringing messages from the front.
The raptors have returned with a vengeance,
even nesting here in the capital.
Most of us have no idea what is going on above us,
but there are a few intrepid types
climbing high up to Peregrine level.
Peregrine! Mark, Peregrine.
When you do get, you know, a large bird of prey
gunning through the centre of London, it's just...
It's a marvel, you know, it really is.
And a phenomenon of only the last ten years.
Up here I can see five Peregrine sites.
There are up to around 23, 24 pairs now.
In the early days, it was probably three pairs in London.
Beautiful. Beautiful.
And it's not just Peregrines they're looking for.
- Buzzard! - Passerine. - Swallow. Just below the horizon now.
Peregrine just below the plane. Swift just above us up here.
- Nice one, Jamie! - Where are we?
Standing on the pinnacle of one of the biggest banks,
each month this group of birders
holds a vigil over the London skyline.
Below them, global finance hangs in the balance.
Up here, they're following global movements too -
migrants from as far as Asia are tracked and logged.
Looks like - talk of the devil - an immature lesser black-backed gull.
Gulls are fascinating, but they're an acquired taste for a lot of people.
You'll often look up and if there's a very distant speck soaring,
thermalling like raptors, more often than not it's a cormorant or a gull.
They're kind of like the ground mass that you're working through
to try and get to the good stuff.
Most birders are solitary types.
This gathering is a rare collaboration,
each of them coming together from their own special patches of London.
It seems to be coming closer towards us.
You might get some film here, yeah.
- We communicate online a lot, don't we? - Yeah.
And we're always seeing things in different parts of London.
We actually met up here, didn't we, Pete?
- Yeah. I'd heard of you before. - And you, too.
Yeah, we kind of follow each other's sightings and exploits.
Yeah, we've got our different patches that we cover,
so everyone covers a certain area, and together we all cover the whole of London.
Yeah, gotcha. Cheers, mate.
This is mutual territory,
but what happens if one of them starts birding on another's patch?
That's called poaching. THEY LAUGH
Mark's patch is in the council estates of Hackney.
You mention Hackney to most people
and it does conjure up images of poverty and crime,
the archetypal concrete jungle.
It is the birders who know the wild places of our cities the best.
At dawn, behind the estates,
Mark has a secret oasis.
The hidden nature of the city
can be better than anything found in the countryside.
Living here has really intensified my appreciation.
It's more isolated, it's more specialised -
I think that creates an enormous sense of well-being,
which you can't necessarily quantify.
You can't really put a price on.
It's a reservoir of London's drinking water
where heron and cormorants have taken up residence.
No self-respecting heron would nest at water level,
but in the city deviant behaviour is more acceptable than elsewhere.
When out on a date, Canada geese may not be deviant,
but they are certainly not gentle lovers.
With the arrival of spring, Mark's secret place
can give up one of the greatest spectacles of London wildlife.
It's a love story -
a courtship ritual that would knock the hardest of urban hearts.
The grebe is a world-class performer.
They represent a dash of real exotica.
You wouldn't think they were out of place in, perhaps,
Africa or Asia, but they're very much a British bird
and they are very much a Hackney bird.
This is the start of the courtship, where they both approach each other fairly fast, heads down.
Straight for each other and then, as they arrive,
the head-shaking and the dance begins.
What the birds are actually doing now
is they're approaching each other with vegetation,
almost like a Valentine's Day present.
It's very much a symbolic offering, almost Egyptian.
It seems like a lot of work for a bit of old weed.
It's not all about value, isn't?
The bigger the rock on your finger, the better the marriage?
I don't think so.
That judging them by human standards,
which is, you know, an extremely flawed way to enjoy nature.
The grebe's display is...
something that's indicative of spring.
I think it's one of nature's signals
that spring is well and truly on its way.
And that makes you happy?
I think... I think it'd be very odd if it didn't make me happy.
While most of us are still supping cornflakes,
Mark's tapping into a Planet Earth special.
Unlike Mark's secluded haven,
over at Pete's patch, there's a riot going on.
It's a huge party, with an all-you-can-eat deal.
For them, it must be heaven.
Because they're scavengers, so it's the ultimate scavenger paradise.
They've got more food than they can wave a stick at.
London's waste attracts
one of the greatest gatherings of gulls in the country.
To be close to this,
Pete has even bought his house overlooking the site.
When the wind is blowing from the East
it can actually get almost unbearable some days.
This is junk food - literally.
The gulls' success is all about the distinct lack of fussiness.
It's not just the fast food that lures them in -
around the coast, there's no longer the same opportunities
for seagulls to socialise en masse.
This is one big seagull party.
Herring gulls got their name
because they followed our boats for the herring we threw overboard.
There are over 2,000 of them here,
yet on the coastlines of Britain, they're becoming endangered.
In the future, London's children may wonder
why they are called herring gulls.
The relationship these birds once had with fishermen out to sea
will have been lost for the pull of the city.
Herring gulls, lesser black-backed gull...
Where we see a mass of birds, Pete sees rare individuals.
There should be greater black-backed here as well.
There's one there now, look. Going past that bulldozer.
It's hovering. Down and right.
Coming towards us, just a single bird, there.
Some of them come from a very long way,
you know, all over Scandinavia, Norway, Finland...
We get Caspian gulls here as well - they've come from central Asia.
Uh, we get, um...
We get Iceland gulls, which come from Greenland.
We've had gulls that have come from as far as Alaska.
There could be up to 15,000 gulls here today.
That's a lot of birds.
Every hour in Britain,
we throw away enough rubbish to fill the Albert Hall.
It's not just the gulls that are cashing in on this.
Foxes like to scavenge, too,
but the swirling mass of live food above his head is just too tempting.
Old instincts die hard.
- SOMEONE WHISTLES - This vixen has learned to do an extraordinary thing
for an even more reliable source of food.
First, all she has to do is follow the whistle.
SOMEONE WHISTLES
Then she's learned that sitting politely is a small price to pay
for a steady stream of sausages.
Do you want this?
Sit.
Good dog.
And I just call her White Legs. She's the mother.
And this one's Greedy. Yeah?
You want this? Fox. Sit.
Sit.
Good dog.
You see? He sits.
Do as your mother tells you.
There are four or five foxes who have this relationship with Lillian.
The White Legs is the mummy. She's got five little ones to feed.
Greedy, I think, is her sister.
You want this one, Greedy?
We've got two Greedys here and they've got the daddy there.
Sit. Sit. Sit.
- But, of course, this isn't just about the foxes. - Good dog.
This is about our need for a connection with nature.
This is about a lady high in a concrete tower
who finds solace through the animals below.
Oh, the other one's there. That's three, that's four there. Sit.
Now, watch him. When we give him...
He'll go straight over there and take it to the little one.
- Hey! - SHE LAUGHS
Now he's got it, he's going to go. He's going to go.
Yeah, here he goes. Go on. He's gone to where the cubs are.
Only we humans go out of our way
to intentionally sustain another species.
I'd like someone to feed me if I was out there,
especially if I've got five cubs.
You want this? Sit.
Sit.
When animals respond to us, they can bring extraordinary joy.
And that can come in many forms.
For a chef in Bethnal Green, it's not foxes -
but sparrows are important in his life.
For Cyrus, these small birds are a reminder of his childhood in India.
Ah, look who's here - a good friend.
There's one bird I grew up with in India,
and we had hundreds of them there. They used to perch inside our house
and we used to get little sparrows coming out and I used to
actually have them in my hands sometimes. So sparrows make me very happy.
I was amazed when I first came here that the sparrows were dwindling
and I didn't see many sparrows. I only saw them in a few places.
It's an amazing bird - very industrious, very hard-working
and every one of them has got a character.
If Cyrus is to help his little friends here in London,
then he must do battle with an invader
that some consider to be overrunning the city in plague proportions.
My biggest problem is the squirrel.
A squirrel becomes cleverer by the day.
What I'm going to do now is apply lots of Vaseline on that bar,
and just really keep on smearing Vaseline, coat after coat.
Cyrus is an award-winning chef and he has another trick up its sleeve.
To ward off my little devil four-legged friend,
who seems to get into everything,
I mixed some crushed chilli seeds inside.
I know it's a bad thing to do because I love animals of all kinds,
so I won't kill him, but what I will do is keep him away from here.
So the chillies get into his nose and it's amazing
because he takes a somersault, he takes a backward flip,
shakes his head about, and he doesn't come back.
If you tried to eat a spoonful of that, you'd be suffering miserably.
London is amazing from the point of view that
there is still so much wildlife.
Just look on the canal in the early morning.
The swans are floating past, the geese are there,
the ducks are there, the coots are there, of course, crazy as they are,
screaming and shouting at two in the morning, waking me up sometimes.
In India, they would be cut.
Somebody's little dinner would be ready.
You just see birds floating around like that, aimlessly.
They would get them. If you come from a city like Bombay,
wildlife has virtually been exterminated.
Where I grew up, in our little suburb of Bombay, we had snakes,
we had monitor lizards, we had parakeets, parrots, the lot.
I don't see a single bird now.
There is no city like London in the world.
The amount of parks we have got, the amount of open spaces we've got,
tiny little spaces also are green.
I think that is something that London needs to be really proud of.
Coming from India, of course, this is like magic.
'Good morning, London. It's five minutes past six.'
'As London basks in a mini heatwave,
'it's perhaps difficult to imagine the capital...'
'Phew, what a scorcher!
'If you watched John Hammond a bit earlier on the national weather,
'you'll know the hotspot today is Northolt in north-west London.'
London is indeed magical.
It is home to eight million people,
yet each day throughout its history
it has greeted a wild population bigger than its human count.
'Habitats on land and in water are still works in progress,
'but already drawing praise.'
'The rivers look a lot cleaner.
'Everything's been trimmed down, so it's wonderful.'
The rivers are now full of fish,
grebes and herons, even otters are back.
Peregrines and gulls fill the sky.
It's one of the greenest cities in the world.
Away from the canyons of the city,
rising above the floodplains of the Thames,
lie the ancient oak forests of Richmond.
This is a place where Old England still remains,
that harks back to the original habitat of London.
This man is no stranger to the history of these woods.
Nice old oak trees here.
Massive, big, old tree.
These are probably 400,500 years old.
Henry VIII probably alive when these trees were around.
He's probably done what I've done,
just lent against it while he's chasing the old deer.
It's almost like Robin Hood country.
You expect to see a bloke come out in a pair of tights in a minute.
It's John's job to manage the deer here.
He's been a London gamekeeper all his life.
There was a female here a minute ago,
cos she's got a baby here somewhere.
Right now, he's looking for a fawn.
At the start of summer, the mothers stash their young in the grass.
It's the one time when female deer are aggressive to anything
they think may be a danger to their calves.
There's a hind watching. Be careful of her.
She's got one here somewhere.
Most at risk are the dog-walkers in the park.
If we had a dog here, you'd be in serious trouble.
I mean, if there was a dog chasing a calf here now,
all of those hinds and those up there,
there'd be 50 hinds chasing the dog. And God help the dog!
Their feet are called slots
and they're extremely sharp on the tip end of the toe.
We have had dogs killed here.
Got some people here with dogs which are going to be in trouble,
cos they're heading right towards them.
If you let the dog off the lead, actually,
and if it was scared of deer and was running away,
you could run away with it and it would attack the dog, not you.
You'd get away that way.
With the deer distracted by the dogs,
it's a good opportunity to sneak in to catch a young fawn.
Got one, just down here.
It's 20 feet in front of me now.
Hopefully, if I can just walk up to it and just hold it, you know,
come in slowly, keep it calm, there's less chance of it bleating.
But once it bleats, we've got some girls behind us, some hinds...
Once he bleats, we've got to get out fast because they'll come running.
John wants to tag the young deer.
They will not move for anything.
Catching it is the easy part.
But avoiding the attention of the females is the problem.
Let me get an ear tag in fast because...
BLEATING
CONTINUES BLEATING
Number ten. There you are.
Oop! Get out of here quick. Here come the girls.
Stay with me, John.
You see what I mean? You have to be careful.
But I would back out now if I were you guys.
She's going to follow us, see.
Just keep walking.
The tags help track the fawns as they grow up.
Come winter, many of the deer will have to be culled
in the dead of the night.
We'd all like to live in an ideal world,
where predators will take care of things,
but we're not in that world no more.
You know, if you didn't cull these deer, I mean,
they produce between 100 and 150 babies every year.
And you've got to think, you've only got to give it three, four years,
you'll have doubled your herd size.
Then, anything green you're looking at will be gone
cos they'll have eaten it all.
There'll be nothing left.
Who wants a park like that?
Here, nature has been managed and controlled
since Charles I built a wall around Richmond
and claimed it as his garden.
I'm afraid you have to act as God.
The really wild spaces of London are somewhere else.
not the parks and gardens,
but the forbidden zones.
The railway verges
are some of the most important and undisturbed green spaces in London.
Behind electric fence and barbed wire,
they are as difficult to reach as any sea cliffs or deserted island.
They thread through London like green arteries.
Plants which normally live oceans apart
find their place to thrive and reach every corner of the city.
Here, the seeds of ragwort, knotweed and willowherb
commute on the slipstream of the Circle, District or Northern lines.
Here, foxes and feral cats migrate through the city,
seeking their fortune.
And there's another animal that is rumoured to be using our rail links.
If it's true, then pigeons have taken their relationship with London
to a whole other level.
Pigeons visit stations because there are plenty of crumbs about.
But Londoners are reporting a new phenomena.
Some birds, after feeding at one station,
are happy to go to the next one...by train.
'Bad news for commuters - fare rises and tube strikes.
'The RMT has announced a series of walk-out dates.'
'That's right. Four days of strikes have been announced,
'all for the second half of this month.'.
'South West Trains has said it will review the way it deals with disruption to its services..'
PA: This is a Circle line train via Paddington and Baker Street.
This train is ready to depart. Please stand clear of the doors.
Is this a new kind of evolution?
PA: The next station is Goldhawk Road.
PA: This is Goldhawk Road.
This is Hammersmith & City line train to Plaistow.
It's certainly a nice life if you can get it.
Travelling by train, visiting friends in the park,
constantly fed by the upright apes all around you.
But a pigeon doesn't have it all its own way.
There are dangers here, too.
There are 300 languages being spoken in London.
And the multicultural flavour of the city
is reflected in the animals that live here.
The pelicans have been here since 1664,
a gift from a Russian ambassador.
They seem prepared to get along with the locals.
It's hard to know what sort of behaviour to expect
from a Russian pelican living near Buckingham Palace.
But, surely, this is not normal.
WOMAN: Oh, my God!
ONLOOKERS LAUGH
It's not just the pigeons that have to face
unnatural dangers in the city.
Nesting high in a tree or on a rock face is normal for a duck.
The chicks jump down soon after they hatch.
But this London cliff face is a hell of a leap.
For some ducklings, once in the water,
their troubles are just beginning.
20 years ago,
a ninja cartoon sent kids flocking to the shops to buy baby turtles.
Then, they were no bigger than a 50-pence piece.
Now, a London pond can contain several hundred red-eared terrapins,
all grown up,
and doing what they've always done in the Everglades and the Amazon.
London has always provided a haven to immigrants
from all over the world,
and there's one refugee rumoured to have Hollywood credentials.
Sometimes, dramatic changes may be traced back
to a single human mistake.
These Indian ring-necked parakeets
first centred around London's Shepperton Studios,
and popular opinion has it that they escaped in 1950
from the set of The African Queen.
Humphrey Bogart left a door open for a moment perhaps,
and the wildlife of London was changed.
And dusk, wave after wave of parakeets
can build to a roost of over 6,000 birds.
Of course, London is used to aliens.
Immigrant black rats off the boats brought with them the plague.
Today, it's the Norwegian brown rat
which, in London, can now grow twice the size of its cousins back home.
And new arrivals are still coming in off the boats.
Go dancing down by the docks tonight
and the UV lights of the clubs can reveal more than you bargained for.
The European yellowtail scorpion is rarely lethal,
but you wouldn't want to lie around in this gutter after a skinful.
There are now three separate colonies of scorpion
living in London, some several thousand strong.
Some immigrants arrive on boats, others by train.
This man is hunting aliens that are sneaking their way in
using the old Victorian canals.
Crayfish Bob has ideas of big business down here.
He wants to catch the invaders for us all to eat.
But in these murky depths,
he's stumbled upon a gang war with crayfish invaders
from both Europe and America fighting over territory.
This underworld is the scene for a major turf war.
I would think, in this darkness, this would be a very attractive habitat.
In this old brickwork,
the chances are they'll find crevices to hide away in.
Yeah, I would think that this was
a fairly popular place to reside.
Well, that's a red swamp.
As you see - red swamp - likes living in swamps and...
..is somewhat red.
What we have is four different species of crayfish.
They're all invasive. None of them should be here.
The old gang of white-claw - folklore, gone years ago.
And it's like a gang here and a gang here. It's all about territory.
The Serpentine, for example,
used to be absolutely teeming with Turkish crayfish.
But now the signal crayfish have come in.
Hampstead Heath - once Turkish territory, red swamp move in.
It's like the sort of gangland wars of the '60s.
The gangs are on the move.
In Maida Vale, a red swamp has moved on a signal's patch.
A punch-up is inevitable.
The signal crayfish fights dirty.
He carries with him a plague
that lays low all other crayfish in its path.
He's already wiped out the native crayfish
and his gang is set to take over the whole of London.
He's killed most of our native white-claws in many areas.
He's teeming on the bottom of the rivers, and he's quite likely
to do what he's done in the rest of the UK and become dominant.
In the waterways of London, a new order is being established.
All over London, it's the same.
The ancient residents and immigrants
are pioneering a new future with us in the city.
This unnatural habitat is home for a new generation
and they're growing up in a place that suits them just fine.
An unnatural life in the city
can be easier than anything in the countryside,
never more so than in the winter.
'More heavy snow and freezing temperatures forecast.
'Up to nine inches of snow fell in some areas.'
It's two degrees warmer for a start.
It means pigeons can nest even earlier here.
They may even get a break from the London Peregrines
who've adapted to use the bright lights to hunt bats,
instead of birds.
And when times are tough, for those who look for it,
there's always a little extra food to be found.
Modern life usually creates a barrier between us
and the natural world.
But, just occasionally, technology brings us closer together.
Ernie has his own special relationship
with the foxes he feeds around his nightwatchman's cabin.
ERNIE SHOUTS
It's the shouting out that actually does it.
They seem to get to recognise the voice.
Then he sits back for his own reality TV show, live.
And like Lillian and her foxes, and Cyrix and his sparrows,
he thinks of the wild animals as friends.
You can hear them actually walk across the weigh bridge
and you look up and think, "What's that noise?"
Look at the camera and you can actually see 'em coming across.
Is that one feeding now?
We've got one feeding on the left-hand corner.
Ernie's seeing an important twist in the story.
An old hand at urban living
is threatened by a new migrant to the city.
If the fox is feeding first, they obviously can sense the badger
and they can hear it, they will look around and simply back off.
They walk away.
As his weigh bridge reveals,
this badger comes with a formidable appetite.
10.2 kilos, that one weighed.
They're supposed to dig their own weight in worms a day.
And I can imagine some of them are quite a big animal.
This winter, Ernie's going to be eaten out of house and home.
The fox very rarely will try and intimidate the badger.
If you see the size of the claws,
you can understand why the foxes would walk away.
I'm sure I would as well!
Here comes a car in now.
Maybe in a few years, the badger will also abandon its country roots
for an improvised city life.
MUSIC: "Someone Like You" by Adele
Do you miss the badgers when you're not at work?
Sometimes - when we're talking to the grandchildren.
A couple of times, they'll come down and watch 'em all come out and feed.
Not so much now.
They're growing up and becoming teenagers
and girls become more important than badgers, unfortunately.
We all like a glimpse of an untamed world.
All around us, animals and plants
are being displaced from their natural homes,
colonising the forgotten corners of our cities.
Here, a global mixture of emigres and refugees
have created a new life.
And there's no turning back.
They're Londoners now.
Who knows what weeds in the concrete, or gang of crayfish
or scorpion, parakeets or ninja turtles will arrive next.
Here, the animals have a dependency on us,
but we also have a need for them -
a desire to be in contact with a world
that is not shaped by human hand.
Most people live in cities now, lost in their own world.
They only notice each other.
Yet if they look up into the sky, down an alleyway,
or behind a fence,
they may meet a wild animal, and that could change both their lives.
There is no city like London in the world.
Coming from India, of course, this is like magic.
I've got the job that everybody wants. What could I want for more?
Pleasure. Just simple pleasure,
to know that they're surviving.
I think it'd be very odd if it didn't make me happy.
When you're reincarnated the first time around,
you come back as a bird which, quite often, is a pigeon.
I'd love to come back as a pigeon.
# Never mind I'll find someone like you
# I wish nothing but the best for you, too
# Sometimes it lasts in love But sometimes it hurts instead
# Sometimes it lasts in love But sometimes it hurts instead. #
Subtitles by Red Bee Media Ltd