Crocodiles hail from the great age of reptiles over 70 million years ago.
Since then, the world has changed dramatically...
but amazingly, they have changed little.
They're the only great reptile predator...
to have outlived the dinosaurs.
Ancient they may be but 70 million years on...
they're still the most successful freshwater predator.
Most of the waterways in the tropics these days...
have their own species of crocodile.
How come they've been so successful for so long?
It seems their design when it first appeared was already very advanced...
and it's kept them successful ever since.
This film reveals the nature of that success.
Crocodiles may have scored an early evolutionary bull's eye...
but there's much more to their staying power than brute strength.
Only now, by exploring their complete world...
above and below water, by day and night...
can we fully appreciate just how sophisticated they are.
Underwater, crocodiles have perfect poise.
They can control their buoyancy like a submarine.
To dive, they breathe out which reduces their lung volume.
They can sink without trace.
While submerged a protective membrane closes over their eyes...
like swimming goggles.
Crocodiles are cold-blooded.
They rely on the temperature of sun and water...
to heat themselves up or to cool down.
But when fully charged...
they are capable of breath-taking power and speed.
They're the most dangerous freshwater predator on the planet.
Even Tyrannosaurus Rex couldn't match this winning formula.
It's a design that has allowed them to spread around the tropical world.
This extended family includes alligators of temperate waterways...
Gharials of the Indian subcontinent...
and caiman of tropical South America.
They've even invaded the sea.
Crocodiles have special glands which enable them to tolerate saltwater.
This is how they've colonised new rivers along the coast.
But only a few species can migrate across oceans.
The real specialists, the saltwater crocodiles...
are affectionately known as "salties".
They've been seen 1000 kilometres from land...
encrusted with barnacles, as they search for new island homes.
This pioneering spirit and their unique character...
has made them a universal threat.
Crocodiles deserve their tough reputation...
but they aren't just solitary killers.
In the calm of the Florida swamps we can begin to see them in a new light.
They are reptiles with social skills...
and American alligators are particularly chatty.
During the breeding season...
an expressive chorus of bellows, grunts and hisses...
rises from their densely vegetated swamps.
The males are calling to distant females...
but their bellows sometimes attract rivals.
There are snappy ways to make your feelings known...
if you end up in the wrong company.
The resident male only shows a bit of muscle...
if the rival fails to get the message.
He's made his point and he can now focus on finding a mate.
Vibrations within his muscle walls...
send sound waves rippling out in to the swamp...
powerful enough to make the water dance.
Part of his roar radiates at such low frequency...
that human ears can't hear it.
But these subsonic calls have astounding penetration...
travelling four times faster and further under the water.
Only with special low frequency recordings...
can we appreciate what the female alligator hears.
She finds his romantic rumblings irresistible.
Even though the call may come from the remotest parts of the swamp...
she is soon on his wave length.
Then they have a more intimate conversation...
conducted in body language.
Their relationship is sealed, touchingly.
Crocodiles are extremely sensitive to touch.
Their armour-plated toughness would appear to be only skin-deep.
Such complicated language and behaviour...
is exceptional among today's reptiles...
but crocodiles might provide a tantalising rear window...
on the social life of their ancient relatives, the dinosaurs.
Nile Crocodiles are the most fraternal crocs of all.
Once a year, they hang out together...
soaking up the sun at traditional mating places.
These are far from being lazy afternoons.
The group is very organised...
so individuals keep a careful eye on movements within it.
An adult male, over five metres long, is the centre of attention.
Up to ten females spend much of their time in the water soliciting him.
They bear their throats as a gesture of appeasement.
Body signals are also used by the male.
He shows-off with noisy water displays.
These postures enhance his attractiveness to females.
It is they who often take the lead...
by rubbing themselves along the length of his body.
At first he snubs both of them.
But the rubbing releases a pungent oil from glands under their jaws.
Both sexes are highly sensitive to this crocodile perfume...
and the male answers with his own musky message.
The scent in the water is particularly potent prior to mating.
Several weeks later, the females are ready to make their nests.
Even when basking, adults rarely move far from the water.
It's ironic that the first critical part of crocodilian life...
is spent on land.
Crocodile babies are born encased in eggs but they must still breathe air.
It's essential this mother lays her clutch beyond the high water mark.
The eggs will be so at risk...
from drowning, predators and temperature fluctuations...
that she relies on exactly the same nest position year after year.
These time-honoured sites are a measure of the experienced care...
that crocodile mothers provide.
Once the excavation is complete she lays her eggs in a trance-like state.
She's entering a deep commitment to her offspring.
The hole will become an incubator.
Crocodile eggs will only develop...
if they remain between a steamy 27 and 34 degrees...
so her choice of site is critical.
Nest chambers from equatorial African plains to Himalayan river valleys...
all remain within this temperature range...
but no-one knows how crocodile mothers get it right.
Once the nest is sealed, the mothers keep vigil for 90 days.
Temperature determines the sex of the developing eggs.
A half degree difference between the top and bottom of the nest...
can markedly affect the ratio of males to females.
Given the changes in climate that the world has experienced...
it seems incredible that crocodiles have survived at all.
Overall, enough males and females emerge...
but these baby Nile crocs face more immediate threats to existence.
Raiders might be drawn to their combined noise and smell.
Hopefully their mother will hear their calls and reach the nest first.
Once she digs them out...
they must reach the relative security of water as quickly as possible.
The babies could probably find their own way...
but they are only safe if they stick together.
So their mother transports them to water herself. In her mouth.
The skin of her lower jaw stretches into a hanging cradle...
in which she can carry fifteen or so at a time.
It's a snug fit, once you're in.
Her forty-or-so eggs hatch simultaneously...
so she'll have to make several trips.
The clamourings of the hatchlings...
constantly remind her to return to the nest...
and ensure that no-one misses the last bus.
She releases them into a nursery pool.
They must make the most of her tender loving care.
They have only a few weeks under her watchful eye.
For safety's sake, they call to each other and to her...
conversations which continue into adulthood.
The 18 different sounds they'll use...
represent a vocabulary more typical of mammals than of reptiles.
Unlike mammals, their rate of growth is affected by temperature.
The warmer it is, the quicker the food digests into body bulk.
Over a lifetime under a tropical sun...
they may grow 4000 times bigger than this.
Their mother won't eat at all.
She's protecting her infants from being eaten...
even by other crocodiles.
The mother successfully defends her own brood...
but it's a grim reminder that crocodiles eat just about anything.
Her babies will learn that successful crocodiles...
take all their dietary chances.
Their hunting technique is there from birth.
With eyes, ears, and nose at water level...
they mirror the tactics they'll use as adults.
These shoreline snacks...
may be wildebeest or zebra in years to come.
They rely on communal living to survive this tender age...
but competition between the youngsters is intense.
Despite their mother's protection, only two percent will survive.
The babies of caiman, a type of South American crocodile...
face even shorter odds.
Wildlife may seem abundant in their Venezuelan marsh...
but that's because the water elsewhere is drying up.
Even the fish are out of water.
The dry season is five months long...
but in some years it's more severe than usual.
Unexpectedly, animals can be left high, if not exactly dry.
Eventually some of these watercourses will dry up completely...
leaving many caiman exposed and dehydrated.
Temporary skin relief is provided by this ultimate of face packs.
Mud is an effective crocodilian sun screen.
Cooling water is at a premium.
The remaining pools are becoming overcrowded.
At such pressing times the adults usually rub along.
However, babies could be eaten by them...
so this is no place for a mother to raise her young.
Fortunately they can expect complete maternal attention...
during this five month period of danger.
The shrinking watercourse becomes hazardous for the babies.
Drastic measures are called for.
Night-time cameras reveal they'll make a run for it...
under the cover of dark.
Their escape will be risky, for it is made over land.
Mother leads the way.
It's a while before the babies have the courage to join her.
Calls of reassurance and maybe her musky smell...
encourage the hatchlings out of the water.
She follows good instincts.
Night-time temperatures are safer for tiny cold-blooded bodies...
and there are fewer threats about.
But this is a long march that must be concluded by daybreak.
Their mother's acute sense of smell...
brings them to their watery destination...
with less than an hour to spare.
There's plenty of water for her babies...
to survive the rest of the dry season.
But lots of other females have had the same idea...
and there's only room for one adult.
The mothers must fight, or as is more often the case, simply leave.
Their offspring are far from abandoned.
The remaining female will adopt and protect them all...
over one hundred of them.
This super-mum carries her burden lightly.
Family life may be unconventional but crocodiles do grow up in company.
As hunting adults, this may prepare them for dedicated teamwork.
Especially if there's a rare dish on the menu.
Migrating zebra cross the Mara River in Kenya...
on only a few occasions each year.
Resident Nile Crocodiles can't afford to miss these fleeting chances.
So they co-operate.
From different places under the banks...
they spend days waiting and watching the nervous herds.
Only when the zebra commit themselves to a departure point...
do the crocodiles take up their final positions.
The current drags the zebra downstream...
so five or six crocodiles cover the crossing from different angles.
It's hard work for crocodiles too, but they can submerge...
taking advantage of deeper, slower currents, to move closer.
Their approach is stealthy, measured and tactical...
as if moving in on a chosen victim.
The current is flowing in the zebra's favour.
It buffets the crocodiles out of position and they can't get a grip.
The zebra's wide rump gives it a big advantage.
Adult zebras also have a vicious kick which could break a crocodile's jaw.
That might mean starvation, so crocodiles are also taking risks.
A lot of effort results in little success for the crocodiles.
But only until smaller, more vulnerable animals enter the water.
At any time the zebras can be ambushed by frightening power...
and lightening speed.
The baby zebra faces several waves of attack.
This is the advantage of teamwork.
Most of the year, life along Africa's rivers is even more of a struggle.
The dry season in Zambia's Luangwa Valley can be unsparing.
Even vegetarians are forced to scavenge.
But crocodiles still thrive on the edge.
Far from being dependent on large mammals like wildebeest or zebra...
crocodiles have extraordinarily adaptable diets.
We've not known this until now...
because we've never seen them hunting at night.
What crocodiles do at night has remained a mystery...
because they will only move around naturally in total darkness.
So only with the use of invisible infrared light...
can we see their nocturnal habits for the first time.
In the Luangwa River shallows...
a Nile crocodile hunts for less glamorous prey. It's stalking fish.
Over the year, crocodiles fatten-up on fish and molluscs...
rather than mammals.
Mammals come and go, but the muddy river bottom...
is always a good place to stir up snails, for instance.
The crocodile is a flexible feeder in its methods too.
It uses its armour plated body...
as sinuously as a length of fishing net to corral fish towards the shore.
Within their element, crocodiles equally deserve the title:
"King of the beasts".
Only when the dry season becomes desperate...
are these two great hunters of land and water...
likely to come face to face.
But only the crocodile is bold enough to leave the safety of water...
and meet the lion on its home ground.
Few animals would actively take on a whole pride.
The lions are simply frustrated.
Especially when the smell of their supper...
coaxes other crocodiles out of the water.
Crocodiles have thick skins.
The lions are forced to defend their meal by moving to a different table.
They just leave nothing but scraps behind.
The reptiles have stronger stomachs than the mammals.
Lions can only cope with the chewy parts.
Crocodile digestive juices are so acidic...
that they can break down skin, bone and horn, to be turned into muscle.
There's no such thing as crocodile left-overs.
Their exceptional sense of smell...
enables them to capitalise quickly on the demise of others.
And at the end of the dry season the smell of death is everywhere.
A mother hippo mourns her baby.
Crocodiles have good reason to be wary of adult hippos...
so they wait for the grieving mother to go.
Food, any food, is hard to find.
Crocodiles from up to 7 km away recognise the whiff of opportunity.
One dead hippo attracts over 100 hungry crocodiles.
But there's no feeding frenzy. This is crocodile queuing.
The reason for this patient approach?
Crocodiles have a powerful grip and sharp teeth...
but their jaws don't move sideways. They can't chew.
So they have to eat large animals together.
One or two crocodiles effectively brace the carcass in their jaws...
while others wrench off smaller pieces of flesh...
by spinning their bodies round.
Everyone waits their turn.
With such tolerant table manners...
it might take 24 hours to satisfy the whole queue of diners.
Too readily, perhaps, we have cast crocodiles as ruthless predators...
when they are also well-mannered, adaptable creatures.
And too readily we have called them primitive...
when our own human design...
has yet to stand up to their successful test of time.
In evolutionary terms, the crocodile has every reason to smile.