The freshwater wetlands
and waterholes of Australia
are full of life.
Hosting majestic,
extraordinary...
..and deadly creatures.
They congregate
at these waterways
to eat...
..breed...
(Clacking)
..and rear their young.
It's one of the most diverse
and prolific ecosystems
in Australia.
A vast island continent...
..home to
some of the planet's
most unusual
and fascinating animals.
These are the Secrets of
the Australian Waterhole.
The tropical Far North
of Australia.
It's hotter and wilder than
the milder southern regions.
Up here there are
only two real seasons:
the wet...
..and the dry.
It's October...
..the end of the dry season.
There's been very little rain
for five months.
The hot sun evaporates
moisture quickly.
Birds crowd around
one of the few remaining
shallow pools of water.
These shrinking reservoirs
are a vital lifeline
for animals
looking for water and food.
Day after day, the sun burns
and the land cracks.
Temperatures are high.
(Fire crackling)
Fire and drought are common,
and can be fatal to animals.
Some species avoid
the scorching dry season
by flying away
to more benign areas.
Some bury themselves
and go into a resting phase.
(Thunder rumbles)
In November or December,
the sky turns dark,
the clouds roil.
The wet season arrives.
Three or four months
of hard showers, humidity,
thunderstorms,
and millions upon millions
of gallons of rain.
Rivers burst their banks.
They flood out onto the
surrounding flat savannah...
..linking up to create vast
expanses of shallow wetlands.
The rain also tops up
the existing waterholes
and lagoons.
Frogs are among the first
to wake up.
(Thunderclap)
(Rumble of thunder)
They've been hiding from the
sun in crevices, hollow logs,
or deep down in the mud,
where they buried themselves
in cocoons
made from their own skins.
The aptly-named magnificent
tree frog emerges.
He begins calling for mates
straight away.
For wetland frogs in the Far
North, breeding is urgent.
Water levels are high
right now.
But within the wet season,
water levels still rise
and fall.
He wants to make sure his
eggs don't dry out and die.
So he swings into action
immediately.
Within hours of waking up,
frogs mate
and lay their eggs.
As little as a week later,
tiny but fully formed little
frogs can emerge onto land.
The shallow, temporary pools
that form
on the flat savannah
are preferred for egg laying.
The deeper waterholes
will soon be swarming
with predators:
not the safest place
for tadpoles.
As the rain continues...
..in the waterholes
and lagoons
dormant eggs and larvae
reactivate...
..creating food for insects,
small fish and crustaceans.
At this lagoon, close to
Kakadu National Park,
the water is teeming
with tiny life.
The basis of a remarkable
and complex food web.
(Birdsong)
The plant life revives too.
The rains trigger
the water lilies
to make
their colorful return,
opening their pristine
pink petals
and unfurling
their large leaves.
They survived
through the dry season
by letting their leaves
die off
but keeping their roots
alive.
As they grow and bloom again,
their large leaves
give shelter
for the insects and larvae
that are developing
in the water.
The undersides of
their leaves and stems
are covered with algae: food
for the new invertebrates.
As all this small-scale life
in the wetlands
and waterholes increases,
it attracts larger animals
to predate
on the burgeoning banquet
growing in the waters.
Birds.
Thousands of them.
(Honking)
From familiar ducks...
..to some of the most
extraordinary exotics.
Birds are the kings of
the wetlands and waterholes.
If a waterhole
is deep enough to persist,
some birds may stay
year-round.
Others,
like these magpie geese,
migrate from other parts
of Australia
to these fresh
feeding grounds,
taking advantage of
the new and watery world
brought by the rain.
(Squawking)
The magpie geese
are vegetarian.
They're looking for the seeds
of wild rice.
(Squawking)
But others, like this egret,
are here for
the new explosion of fish,
insects and crustaceans.
Different types of beak
or bill
help each species to catch
its favorite food.
The glamorous glossy ibis,
with its iridescent plumage,
is a crustacean lover.
With its curved beak it can
probe the mud to find food.
Weird and wonderful birds are
everywhere at the waterhole.
The spoonbill is another
unmistakable visitor.
There are two kinds
in Northern Australia.
The royal spoonbill has
a black face and legs.
The yellow spoonbill has
a pale bill and legs
and is slightly larger.
There's no mystery
to their name.
The birds swathe
their namesake bills
from side to side
in arcs of over 90 degrees
as they move through
the water,
searching for small fish,
crustaceans
and other invertebrates.
Sensory organs
on the spatulate bill
pick up any movement, helping
them feed in murky water.
Once they detect prey,
these strange beaks
snap shut on the victim.
(Birdsong)
The blossoming insect life
provides food
for many of the birds.
The willie wagtail tends to
stay firmly on dry land
by the water's edge,
looking for crawling
and hopping insects
like ants, termites
and grasshoppers.
Despite his name,
he's actually part of
the fantail family of birds,
rather than the wagtails.
A very familiar sight
in Australia,
he lives in almost
every kind of habitat
apart from dense forest.
He can't resist
the insect buffet
that's appeared
at the waterside.
The pied stilt scours
the surface of the water
for insects that skate,
hover or fly.
It uses its long legs
to stride a little way out
into the water.
But it hasn't got the reach
of the jacana.
Nicknamed the lily trotter,
it uses the lily pads
as stepping stones
to penetrate further into
the heart of the waterhole
and find different insects.
The jacana is also called
the Jesus bird
because it looks as though
it's walking on water.
Its enormous feet distribute
its weight over the lily pad.
(Heavy rainfall)
As the wetlands
and waterholes fill up,
there are some more
new arrivals.
The pelicans have appeared,
to exploit
the profusion of fish.
They may have come
from the coast.
These pelicans
are opportunistic
and go wherever
feeding grounds are good.
They have one of the longest
bills of any living bird.
It can grow up to
one and a half feet long.
The pouch-like bottom section
is elastic in nature.
(Honking)
The expandable pouch
scoops the fish up,
along with all
the surrounding water.
(Honking)
The hook
on the end of the bill
helps them grip on to
especially slippery fish.
(Honking)
They squash down
their pouches
and drain the water out,
leaving just their catch,
which they swallow whole.
(Honking)
The pelicans
patrol the waters in groups,
honking away.
(Honking)
Although they like
to live together,
sometimes they can be
rather cantankerous.
(Splashing)
(Honking)
All this commotion attracts
one of the waterholes'
top predators.
A freshwater crocodile,
known as a 'freshie'
in Australia.
It lives in rivers
and freshwater estuaries
during the dry season,
but with the prolonged rain
of the wet
comes flooding
of the plains...
..and the opportunity
to travel to new
feeding grounds.
Usually smaller than
its saltwater cousin,
the freshie also has
a narrower snout.
This nose shape
means better stealth
and speed in the water.
It feeds mainly on
aquatic life:
fish and crustaceans,
as well as the frogs
and turtles
that are now abounding in
the wetlands and waterholes.
It's an ambush hunter...
..waiting until
one gets close...
..and springing the trap with
a sideways snap of its jaws.
As it gets larger,
the freshie will also
go for mammals
like water rats
and waterbirds.
Crocodiles have been
on the planet for around
200 million years,
outliving the dinosaurs.
Although they can still be
plagued by flies.
Water is many times denser
than air,
so streamlining is necessary
for animals that need to swim
at high speeds underwater.
Even though this freshie
spends much of his time
motionless,
he has a classic
torpedo shape
for maximum
hydrodynamic efficiency.
His webbed back feet
help him maneuver into
the perfect position.
And his powerful tail
propels him silently
through the water...
..as he sneaks up on
an unsuspecting pelican.
After a morning hunting,
the freshie clambers
onto land
to warm his body in the sun.
He's an ectotherm,
and uses external heat
to control
his internal temperature.
Although this does make him
dependent on the weather,
one advantage is that
the freshie
doesn't need to feed as often
as warm-blooded animals
like birds and mammals.
He can go without food
for months if he needs to.
As well as fish, the freshie
will take any mammals
that venture too close
to the water.
(Flapping of wings)
A flock of little red flying
foxes comes in to roost.
These bats
like to base their colonies
near large bodies of water
like this waterhole.
In addition to
a secure water source,
waterholes may also
give them a landmark
that helps them navigate back
from their feeding areas.
Every evening they set off
en masse to find the nectar,
fruit and blossoms they eat.
The bats swoop down
and take a sip from the water
whilst on the wing.
But that drink
could cost them their lives.
(Screeching)
This ambush predator
has a special adaptation
that means the freshie
can break the surface
of the water
without a single
giveaway ripple.
He can move vertically
up and down on the spot,
without swimming
or twitching a limb.
Eyes and nostrils emerge
softly, slowly,
with total control.
But he's not simply using air
as a floatation device.
The croc is actually moving
entire organs around
to achieve this shift
in buoyancy.
Using a muscle
at the back of his diaphragm,
the freshie shifts
the position of his lungs.
To sink, he draws the lungs
back in the body,
towards the tail.
To rise,
he relaxes that muscle,
moving the lungs forward.
And the freshie has
a specialized throat
so he can open his mouth
underwater to capture prey
without swallowing
lots of water.
When the mouth opens,
part of the tongue,
called the palatal valve,
closes off the opening
to the throat
so the mouth
can fill with water,
but none of it enters
the stomach or lungs.
Meanwhile, air inhaled
through the nostrils
enters behind
the palatal valve,
allowing the freshie
to keep breathing,
even when his mouth
is full of water.
(Thunder rumbles)
All the waterhole inhabitants
have their own ways
of getting oxygen.
The fish absorb
dissolved oxygen
in the water
with their gills.
Birds have lungs like humans,
but also possess air sacs
that work like extensions
of their lungs,
so they have fresh,
oxygen-rich air
in their bodies all the time.
Rather than a diaphragm,
they use
muscular contractions
of their ribcages
to move the air in and out.
Amphibians have lungs,
but can also breathe
through their skin.
The crocs'
stealthy breathing system
also means
they can go undetected
as they ambush their prey,
with no giveaway bubbles.
They have excellent
binocular vision...
..but even if they're in
dark water full of mud
they have tools
that enable them
to constantly map
their environment.
Sense receptors
on their bodies
tell them
when water pressure changes
or if there's a disturbance
which could mean
dinner is served.
The young freshie here
has his eye on a pelican.
But his eyes are bigger
than his stomach.
He's got a few more years
to grow
before he can tackle
a bird this size.
In fact, at this size
he's nowhere near
fulfilling his role
as the apex predator.
Right now, he's on the menu
of other animals himself.
A water python is silently
poised at the water's edge.
It's a non-venomous snake
that kills
by constricting its coils
and suffocating its prey.
It mainly feeds on rats
and other small mammals,
but if this snake
gets big enough,
it will take
a baby crocodile.
Especially a nice little
bite-sized one like this,
just a few weeks old.
(Splash)
Not today.
The water python
is a stealthy hunter,
but the croc's ability
to sense differences in water
pressure gives it an edge,
and the baby makes its
getaway in the nick of time.
And the snake itself,
like everything else
in this intricate food web,
is potentially food
for another animal.
(Birdsong)
At first glance,
the ecology of the waterhole
may look like
a simple food pyramid,
with the plankton
feeding insects,
which feed fish and birds,
which in turn feed bigger
animals like the freshie.
But the real law
of this watery jungle
is that all the animals eat
whatever will fit into
their mouths at the time.
For example,
many fish eat larval beetles,
but as the surviving beetles
grow larger,
they can, in turn,
prey on young fish.
So at the waterhole, what
goes around, comes around.
The snake may be a hunter,
but it's also a favorite meal
for one of the rulers
of the wetlands.
It's not an obvious predator.
It has no sharp teeth,
claws or coils.
It's the jabiru.
The jabiru,
or black-necked stork,
is Australia's only
stork species.
The females have golden eyes.
The males, dark.
She's around four feet tall,
with an eight-foot wingspan.
She has a heavy,
foot-long beak...
..capable of spearing
straight through
a hard turtle shell.
The jabiru reigns supreme
among the waterhole birds.
This heron has just caught
a snake for lunch.
But the jabiru lets the heron
know who's boss.
The jabiru eats everything
the waterhole has to offer,
from tiny fish and insects
to baby crocs.
Like the spoonbill,
it feeds by touch,
foraging
in the shallow water.
Holding its bill at around
a 90-degree angle
to the surface,
it can feel sensations
in the water and mud
that tell it
when prey is close.
Then it snatches it up
or skewers it
with its bayonet bill.
(Birdsong
and insects buzzing)
Many of the other
waterhole birds
have a similar shaped beak,
sturdy and sharp.
Ideal for catching fish.
The beautiful
azure kingfisher
launches aerial strikes
from an overhanging branch.
He dives into the water
at high speed,
targeting an unsuspecting
victim in his beak.
Back on his perch,
he kills the fish
by bashing it on the branch,
before eating it.
While the kingfisher
needs his prey to be
fairly near the surface,
some birds can go deeper,
widening their prey base.
The herons and egrets
use their long legs
to wade out and stalk fish.
Once they've zeroed in
on their target,
they jab their dagger-like
beaks down and impale it.
All the animals of the
wetlands are interconnected
in a multi-layered web
of life,
whether predators and prey
in a food chain,
or in their relationships
with other species
at the same level.
The grebes like to hang out
close to the ducks.
The vegetarian ducks
are looking for
underwater plants to eat.
As they agitate
this layer of vegetation,
they're disturbing
all the nearby fish.
The grebes see their
opportunity and move in.
As the fish flee from
the disturbance,
they're easy pickings
for the grebes,
who make
fairly prolonged dives
to snatch up
the panicking small fry.
One of the champion fishermen
of the waterhole
is the Australian darter.
It's fishing
with just its head
and snaky neck
above the waterline.
This expert angler dives down
deeper than most of
the other fishing birds,
around three feet
below the surface,
where he uses his strong,
pointed beak
to transfix his victim.
Being able to dive deeper
means there's reduced
competition with the birds
that are taking fish
from the surface levels.
But birds, with their hollow
bones, are naturally buoyant.
So the darter has
an amazing adaptation.
Its feathers have
a microstructure that,
rather than repelling water,
actually allows it in,
so the bird can sink.
Once near the prey,
it can uncoil its kinked neck
at lightning speed,
to spear the fish.
These special feathers
are ideal for fishing,
but they're poor insulation.
So, after diving,
the darter hangs itself out
to dry in the sun.
(Chirping)
(Chirping and squawking)
All the food here
in the wet season
means it's a good place
for the jabiru
to bring up their babies.
They stay together for
at least one breeding season.
They've chosen a nest site
near the water's edge
and built a massive nest
around three feet wide
from sticks and woody debris.
These chicks are just over
three weeks old.
They develop rapidly.
The babies already weigh
almost one and a half pounds.
The pair share nest-building,
incubation
and chick-minding duties
and maintain
a close relationship.
As one of them returns
to the nest after foraging,
they greet each other with a
graceful dance-like display.
(Clacking)
With wings outstretched,
they gently clack their beaks
and flutter.
(Clacking)
(Clacking)
This can go on
for over a minute.
(Clacking)
Both parents
bring the chicks food...
..small fish
which they regurgitate.
The chicks
swallow them whole.
It's mid-November,
and the chicks will fledge
in just another nine
or ten weeks,
although they'll still get
food from mum and dad
for some weeks after that.
It's a long-term commitment.
They'll be together
for around six months,
from mating, through hatching
and extended chick-rearing.
So it's difficult for them
to breed every year.
Many pairs mate
every other year.
At around four months old,
the chicks will start to find
their own food.
At first, they'll be
going after smaller prey
like small fish and insects.
But they'll have
lots of competition
for the tiny fish.
Large, predatory fish
lurk here too.
The barramundi,
known in Australia as
a delicious edible fish,
is itself very good
at getting dinner...
..able to use
its bucket-like mouth
to suck prey in
from over eight inches away.
Perhaps the most
skillful hunter, though,
is the archer fish.
Living in mangrove swamps,
rivers and streams,
it doesn't look like much
at first.
But it can do...this.
This feat of marksmanship
is even more impressive
than it looks.
Archer fish
can actively control
everything about their jets:
speed, angle,
height and force.
Controlling a free jet
of water like this
is something that's
challenging for humans...
..but for the archer fish,
it's all child's play.
If an insect is in range,
to the archer fish,
it's already history.
When the archer fish
takes aim
at an insect
on an overhanging branch,
its eyes are underwater.
Light bends
when it enters water,
so the fish must make
a calculation
about where the prey
really is
and correct
for the bending of the light.
That's easy maths
for the archer fish.
It must also adjust
for gravity.
Water jets don't travel
in a straight line
because the force of gravity
pulls them down,
changing their angle.
But the archer fish
is able to work out
this tricky physics problem
too and compensate for it.
Bullseye.
And researchers have
discovered something
about the archer fish
that explains how it's able
to hit an insect
with enough force to stun
and dislodge it
up to six-and-a-half feet
away.
Most ballistic objects, like
bullets, when shot upwards
will slow down due to
air resistance and gravity.
But the water jet
of the archer fish
actually speeds up
as it goes further.
As the fish lets fly with its
jet, it modulates the stream
so that the tail end
of the jet
is moving faster
than the leading end.
As the back end catches up
with the front end,
it combines into one big
super-blob
that moves even faster.
The energy that was
dissipated over an arc
is now condensed into
a high-power ball of water
that blasts the unsuspecting
insect from its perch.
Waterhole life
is a complex web.
Distinctions between
the hunter and the hunted
are often unclear.
The whole ecosystem
is in a delicate balance,
but it works.
There is, however,
something that's capable of
not only throwing
the system out,
but completely destroying it.
The cane toad.
Originally from
Central and South America,
cane toads were introduced
to Australia in the 1930s
to try and control pest
beetles in sugar cane crops.
But the toad has become
a ticking time bomb
for native species.
Its upper surface
is covered in glands
that exude
highly poisonous toxins.
Many native animals
eat frogs and toads
as a natural part of
their diet,
so they unwittingly eat the
cane toads: a fatal mistake.
And that's not all.
If the toads happen to die
near a water source
like the wetlands
or waterholes,
their bodies
will contaminate the water
and kill any animal
that comes to drink it.
Even cane toad tadpoles
are poisonous.
They look virtually identical
to harmless tadpoles,
which are a vital food source
for many fish and birds.
These toxic toads
are expanding their range
westwards across the country
at a steady pace,
and are a complete disaster
for native wildlife.
(Thunder rumbling)
After three or four months of
glorious, life-bringing rain,
once again,
the seasons start to move on.
By March,
showers become lighter
and more intermittent.
Little by little,
the dry season returns.
As the dry season
intensifies,
the wetlands and waterholes
begin to shrink back.
The water's edge
turns to thick mud.
The once lush plant life
begins to dry up.
Life for all the animals
gets harder.
The migrants leave for
wetter, fresher pastures.
(Panting)
But for the dingo,
the shrinking water presents
a new opportunity.
He's probably been searching
the nearby wild country
for prey: small mammals
like rabbits or rodents
are favorites.
As the center of
local animal life,
the waterhole
is also a prime spot
to see if there's anything
to eat.
The dingo is
an opportunistic feeder
as well as an able hunter.
If something succumbs to
starvation or disease,
he'll take advantage of it.
He's a regular visitor
to the waterhole.
Especially as the waters
recede,
leaving thick, cooling mud
behind.
As an apex predator,
the dingo is good
for the ecosystem.
It keeps down the numbers
of feral cats,
an introduced species which,
along with the cane toads,
has wrought total havoc
on native animals.
Today, the dingo's just
taking advantage
of the facilities.
As the rainfall slackens off,
for some species
this is a time of plenty.
All the food
concentrates into
diminishing pools of water
and becomes easier prey.
The extremes of a monsoonal
climate in the far north
have led to
a 'boom or bust' ecology.
Times of plenty
followed by hard times.
The wildlife here
has adapted to that.
Magpie geese
switch from eating rice
to eating high-energy starchy
tubers like water chestnuts,
which they dig up
with their hooked beaks.
Some of the frogs cocoon
themselves in the mud,
awaiting reactivation
when the next rains come.
The crocodiles start eating
less as the seasons change
and food becomes more scarce.
They too can dig themselves
into the mud
to rest through the dry.
The leaves of
the water lilies
will once more die off.
Some freshwater turtles
wait for the dry season
to lay their eggs
in sand banks.
Inside the eggs, the embryos
develop for around 70 days,
but then go into diapause,
a state of stasis.
In this dormant condition,
they wait until the next lot
of heavy rain or floodwater
reaches the nest.
Then all the hatchlings
will burst out of the nest
at once.
To avoid the worst
of the drought,
the jabiru
will simply take off
and fly to less ephemeral
water sources.
As can the spoonbill
and the rest of the birds.
The smaller lifeforms,
like crustaceans,
have their own ways
of ensuring
the next generation
lives through the dry.
Some have eggs that are
resistant to drought,
and so tiny they can be
borne on the wind.
Wetlands and waterholes
are a stunning microcosm
of Australian biodiversity.
(Honking)
They're the natural
storehouses
for thousands
of different species.
The magnificent jabiru...
(Clacking)
..the freshwater croc,
both hunter and,
in its youth, the hunted,
aquatic sharpshooter,
the archer fish...
..turtles and wading birds
all take advantage of the
limited time of abundance
the wet season brings.
Playing their part in the
vivid, interconnected life
of the wetland and waterhole
ecosystems.
♪♪
