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AnimalsTranscript
00:00 The freshwater wetlands and waterholes of Australia are full of life, hosting majestic,
00:07 extraordinary and deadly creatures. They congregate at these waterways to eat, breed and feed
00:22 their young. It's one of the most diverse and prolific ecosystems in Australia. A vast
00:47 island continent, home to some of the planet's most unusual and fascinating animals. These
00:54 are the secrets of the Australian waterhole.
01:12 The tropical far north of Australia. It's hotter and wilder than the milder southern
01:19 regions. Up here there are only two real seasons, the wet and the dry.
01:29 It's October, the end of the dry season. There's been very little rain for five months.
01:54 The hot sun evaporates moisture quickly.
02:01 Birds crowd around one of the few remaining shallow pools of water. These shrinking reservoirs
02:23 are a vital lifeline for animals looking for water and food. Day after day the sun burns
02:30 and the land cracks. Temperatures are high. Fire and drought are common and can be fatal
02:52 to animals. Some species avoid the scorching dry season by flying away to more benign areas.
02:59 Some bury themselves and go into a resting phase. In November or December the sky turns
03:11 dark, the clouds royal. The wet season is the most dangerous.
03:22 The wet season arrives.
03:29 Three or four months of hard showers, humidity, thunderstorms and millions upon millions of
03:36 litres of rain.
03:43 Rivers burst their banks. They flood out onto the surrounding flat savanna, linking
03:50 up to create vast expanses of shallow wetlands. The rain also tops up the existing waterholes
04:11 and lagoons.
04:18 Frogs are among the first to wake up. They've been hiding from the sun in crevices, hollow
04:25 logs or deep down in the mud where they bury themselves in cocoons made from their own
04:32 skins.
04:38 The aptly named magnificent tree frog emerges. He begins calling for mates straight away.
04:45 For wetland frogs in the far north breeding is urgent. Water levels are high right now.
04:55 But within the wet season water levels still rise and fall. He wants to make sure his eggs
05:03 don't dry out and die. So he swings into action immediately.
05:10 Within hours of waking up, frogs mate and lay their eggs. As little as a week later
05:19 tiny but fully formed little frogs can emerge onto land.
05:26 The shallow temporary pools that form on the flat savanna are preferred for egg laying.
05:32 The deeper waterholes will soon be swarming with predators, not the safest place for tadpoles.
05:39 As the rain continues, in the waterholes and lagoons dormant eggs and larvae reactivate,
05:49 creating food for insects, small fish and crustaceans.
06:02 With this lagoon close to Kakadu National Park, the water is teeming with tiny life.
06:09 The basis of a remarkable and complex food web.
06:17 The plant life revives too. The rains trigger the water lilies to make their colourful return,
06:26 opening their pristine pink petals and unfurling their large leaves.
06:33 They survive through the dry season by letting their leaves die off but keeping their roots
06:40 alive. As they grow and bloom again, their large
06:46 leaves give shelter for the insects and larvae that are developing in the water.
06:55 The undersides of their leaves and stems are covered with algae, food for the new invertebrates.
07:02 As all this small scale life in the wetlands and waterholes increases, it attracts larger
07:14 animals to predate on the burgeoning banquet growing in the waters.
07:21 Thousands of them.
07:28 From familiar ducks to some of the most extraordinary exotics.
07:48 Birds are the kings of the wetlands and waterholes.
07:56 If a waterhole is deep enough to persist, some birds may stay year round.
08:03 Others, like these magpie geese, migrate from other parts of Australia to these fresh
08:33 feeding grounds, taking advantage of the new and watery world brought by the rain.
08:40 The magpie geese are vegetarian. They're looking for the seeds of wild rice.
08:56 But others, like this egret, are here for the new explosion of fish, insects and crustaceans.
09:24 Different types of beak or bill help each species to catch its favourite food.
09:31 The glamorous, glossy ibis, with its iridescent plumage, is a crustacean lover.
09:39 With its curved beak, it can probe the mud to find food.
09:53 Wild and wonderful birds are everywhere at the waterhole.
10:00 The spoonbill is another unmistakable visitor.
10:05 There are two kinds in northern Australia.
10:10 The royal spoonbill has a black face and legs.
10:15 The yellow spoonbill has a pale bill and legs and is slightly larger.
10:22 The birds swathe their namesake bills from side to side in arcs of over 90 degrees as
10:29 they move through the water, searching for small fish, crustaceans and other invertebrates.
10:36 Sensory organs on the spatula bill pick up any movement, helping them feed in murky water.
10:49 Once they detect prey, these strange beaks snap shut on the victim.
10:56 The blossoming insect life provides food for many of the birds.
11:14 The willy wagtail tends to stay firmly on dry land by the water's edge, looking for
11:20 crawling and hopping insects like ants, termites and grasshoppers.
11:27 Despite his name, he's actually part of the fantail family of birds, rather than the wagtails.
11:35 A very familiar sight in Australia, he lives in almost every kind of habitat, apart from
11:40 dense forest.
11:43 He can't resist the insect buffet that's appeared at the waterside.
11:50 The pied stilt scours the surface of the water for insects that skate, hover or fly.
12:08 It uses its long legs to stride a little way out into the water.
12:15 But it hasn't got the reach of the jacana, nicknamed the lily trotter.
12:22 It uses the lily pads as stepping stones to penetrate further into the heart of the water
12:26 hole and find different insects.
12:33 The jacana is also called the Jesus bird because it looks as though it's walking on water.
12:40 Its enormous feet distribute its weight over the lily pad.
12:53 As the wetlands and water holes fill up, there are some more insects that come out
13:00 and eat the fish.
13:26 The pelicans have appeared to exploit the profusion of fish.
13:30 They may have come from the coast.
13:34 These pelicans are opportunistic and go wherever feeding grounds are good.
13:39 They have one of the longest bills of any living bird.
13:44 It can grow up to half a metre long.
13:51 The pouch-like bottom section is elastic in nature.
14:16 The expandable pouch scoops the fish up along with all the surrounding water.
14:23 The hook on the end of the bill helps them grip onto especially slippery fish.
14:42 They squash down their pouches and drain the water out, leaving just their catch,
14:49 which they swallow whole.
15:11 The pelicans patrol the waters in groups, honking away.
15:16 Although they like to live together, sometimes they can be rather cantankerous.
15:23 All this commotion attracts one of the water hole's top predators, a freshwater crocodile.
15:38 It lives in rivers and freshwater estuaries during the dry season, but with the prolonged
15:45 rain of the wet comes flooding of the plains and the opportunity to travel to new feeding
16:00 grounds.
16:07 To smaller than its saltwater cousin, the freshie also has a narrower snout.
16:14 This nose shape means better stealth and speed in the water.
16:21 It feeds mainly on aquatic life, fish and crustaceans, as well as the frogs and turtles
16:31 that are now abounding in the wetlands and water holes.
16:37 It's an ambush hunter, waiting until one gets close and springing the trap with a sideways
16:44 snap of its jaws.
16:54 As it gets larger, the freshie will also go for mammals like water rats and water birds.
17:05 Crocodiles have been on the planet for around 200 million years, outliving the dinosaurs.
17:12 Although they can still be plagued by flies.
17:27 Water is many times denser than air, so streamlining is necessary for animals that need to swim
17:32 at high speeds underwater.
17:36 Even though this freshie spends much of his time motionless, he has a classic torpedo
17:41 shape for maximum hydrodynamic efficiency.
17:48 His webbed back feet help him manoeuvre into the perfect position.
17:56 And his powerful tail propels him silently through the water, as he sneaks up on an unsuspecting
18:03 pelican.
18:21 After a morning hunting, the freshie clambers onto land to warm his body in the sun.
18:28 He's an ectotherm and uses external heat to control his internal temperature.
18:35 Although this does make him dependent on the weather, one advantage is that the freshie
18:39 doesn't need to feed as often as warm-blooded animals like birds and mammals.
18:48 He can go without food for months if he needs to.
18:55 As well as fish, the freshie will take any mammals that venture too close to the water.
19:03 A flock of little red flying foxes comes in to roost.
19:17 These bats like to base their colonies near large bodies of water, like this waterhole.
19:24 In addition to a secure water source, waterholes may also give them a landmark that helps them
19:33 navigate back from their feeding areas.
19:38 Every evening they set off en masse to find the nectar, fruit and blossoms they ate.
19:46 The bats swoop down and take a sip from the water whilst on the wing.
19:53 But that drink could cost them their lives.
20:00 This ambush predator has a special adaptation that means the freshie can break the surface
20:14 of the water without a single giveaway ripple.
20:20 He can move vertically up and down on the spot without swimming or twitching a limb.
20:27 Eyes and nostrils emerge softly, slowly with total control.
20:32 But he's not simply using air as a flotation device.
20:39 The croc is actually moving entire organs around to achieve this shift in buoyancy.
20:46 Using a muscle at the back of his diaphragm, the freshie shifts the position of his lungs.
20:53 To sink, he draws the lungs back in the body towards the tail.
20:58 To rise, he relaxes that muscle, moving the lungs forward.
21:06 The freshie has a specialised throat so he can open his mouth underwater to capture prey
21:11 without swallowing lots of water.
21:16 When the mouth opens, part of the tongue, called the palatal valve, closes off the opening
21:21 to the throat.
21:23 So the mouth can fill with water, but none of it enters the stomach or lungs.
21:29 Meanwhile, air inhaled through the nostrils enters behind the palatal valve, allowing
21:34 the freshie to keep breathing even when his mouth is full of water.
21:41 All the waterhole inhabitants have their own ways of getting oxygen.
21:50 The fish absorb dissolved oxygen in the water with their gills.
21:57 Birds have lungs like humans, but also possess air sacs that work like extensions of their
22:02 lungs, so they have fresh, oxygen-rich air in their bodies all the time.
22:09 Rather than a diaphragm, they use muscular contractions of their ribcages to move the
22:15 air in and out.
22:21 Amphibians have lungs, but can also breathe through their skin.
22:30 The croc's stealthy breathing system also means they can go undetected as they ambush
22:34 their prey, with no give-away bubbles.
22:41 They have excellent binocular vision.
22:47 But even if they're in dark water full of mud, they have tools that enable them to constantly
22:53 map their environment.
22:57 Stress receptors on their bodies tell them when water pressure changes, or if there's
23:00 a disturbance, which could mean dinner is served.
23:07 The young freshie here has his eye on a pelican.
23:26 But his eyes are bigger than his stomach.
23:32 He's got a few more years to grow before he can tackle a bird this size.
23:38 In fact, at this size he's nowhere near fulfilling his role as the apex predator.
23:45 Right now, he's on the menu of other animals himself.
23:56 A water python is silently poised at the water's edge.
24:03 It's a non-venomous snake that kills by constricting its coils and suffocating its prey.
24:12 It mainly feeds on rats and other small mammals, but if this snake gets big enough, it will
24:19 take a baby crocodile.
24:22 Especially a nice little bite-sized one like this, just a few weeks old.
24:29 Not today.
24:44 The water python is a stealthy hunter, but the croc's ability to sense differences in
24:49 water pressure gives it an edge.
24:52 The baby makes its getaway in the nick of time.
24:56 And the snake itself, like everything else in this intricate food web, is potentially
25:01 food for another animal.
25:08 At first glance, the ecology of the waterhole may look like a simple food pyramid, with
25:14 the plankton feeding insects, which feed fish and birds, which in turn feed bigger animals
25:19 like the freshy.
25:23 But the real law of this watery jungle is that all the animals eat whatever will fit
25:28 into their mouths at the time.
25:35 For example, many fish eat larval beetles, but as the surviving beetles grow larger,
25:43 they can in turn prey on young fish.
25:47 So at the waterhole, what goes around, comes around.
25:52 The snake may be a hunter, but it's also a favourite meal for one of the rulers of
25:57 the wetlands.
26:00 It's not an obvious predator.
26:03 It has no sharp teeth, claws or coils.
26:09 It's the jabiru.
26:15 The jabiru, or black-necked stork, is Australia's only stork species.
26:22 The females have golden eyes.
26:29 The males, dark.
26:36 She's 1.2 metres tall, with a 2.5 metre wingspan.
26:41 She has a heavy 30 centimetre long beak, capable of spearing straight through a hard turtle
26:48 shell.
26:50 The jabiru reigns supreme among the waterhole birds.
26:55 This heron has just caught a snake for lunch.
27:01 But the jabiru lets the heron know who's boss.
27:09 The jabiru eats everything the waterhole has to offer, from tiny fish and insects to baby
27:16 crocs.
27:27 Like the spoonbill, it feeds by touch, foraging in the shallow water.
27:37 It's bill is at around a 90 degree angle to the surface.
27:41 It can feel sensations in the water and mud that tell it when prey is close.
27:48 Then it snatches it up or skewers it with its bayonet bill.
28:05 Many of the other waterhole birds have a similar shaped beak, sturdy and sharp, ideal for catching
28:12 fish.
28:17 The beautiful azure kingfisher launches aerial strikes from an overhanging branch.
28:24 He dives into the water at high speed, targeting an unsuspecting victim in his beak.
28:34 Back on his perch, he kills the fish by bashing it on the branch before eating it.
29:00 While the kingfisher needs his prey to be fairly near the surface, some birds can go
29:05 deeper, widening their prey base.
29:11 The herons and egrets use their long legs to wade out and stalk fish.
29:18 Once they've zeroed in on their target, they jab their dagger-like beaks down and impale
29:28 it.
29:35 All the animals of the wetlands are interconnected in a multi-layered web of life, whether predators
29:44 and prey in a food chain or in their relationships with other species at the same level.
29:52 The grebes like to hang out close to the ducks.
29:59 The vegetarian ducks are looking for underwater plants to eat.
30:04 As they agitate this layer of vegetation, they're disturbing all the nearby fish.
30:11 The grebes see their opportunity and move in.
30:16 As the fish flee from the disturbance, they're easy pickings for the grebes, who make fairly
30:22 prolonged dives to snatch up the panicking small fry.
30:29 One of the champion fishermen of the waterhole is the Australian darter.
30:37 It's fishing with just its head and snaky neck above the waterline.
30:44 This expert angler dives down deeper than most of the other fishing birds, around a
30:49 metre below the surface, where he uses his strong pointed beak to transfix his victim.
30:56 Being able to dive deeper means there's reduced competition with the birds that are taking
31:03 fish from the surface levels.
31:06 But birds, with their hollow bones, are naturally buoyant.
31:13 So the darter has an amazing adaptation.
31:18 Its feathers have a microstructure that, rather than repelling water, actually allows it in
31:24 so the bird can sink.
31:30 Once near the prey, it can uncoil its kinked neck at lightning speed to spear the fish.
31:44 These special feathers are ideal for fishing, but they're poor insulation.
31:51 So, after diving, the darter hangs itself out to dry in the sun.
31:59 [Music]
32:29 All the food here in the wet season means it's a good place for the jabiru to bring
32:33 up their babies.
32:40 They stay together for at least one breeding season.
32:48 They've chosen a nest site near the water's edge and built a massive nest around a metre
32:53 wide from sticks and woody debris.
33:00 These chicks are just over three weeks old.
33:05 They develop rapidly.
33:09 The babies already weigh 600 grams.
33:16 The pair share nest building, incubation and chick-minding duties and maintain a close
33:23 relationship.
33:26 As one of them returns to the nest after foraging, they greet each other with a graceful dance-like
33:30 display.
33:37 With wings outstretched, they gently clack their beaks and flutter.
33:46 [Music]
33:53 This can go on for over a minute.
34:01 Both parents bring the chicks food.
34:11 Little fish, which they regurgitate.
34:17 The chicks swallow them whole.
34:24 It's mid-November and the chicks will fledge in just another nine or ten weeks, although
34:37 they'll still get food from mum and dad for some weeks after that.
34:44 It's a long-term commitment.
34:47 They'll be together for around six months, from mating through hatching and extended
34:53 chick rearing.
34:56 So it's difficult for them to breed every year.
34:59 Many pairs mate every other year.
35:03 At around four months old, the chicks will start to find their own food.
35:08 At first, they'll be going after smaller prey like small fish and insects.
35:15 But they'll have lots of competition for the tiny fish.
35:22 Large predatory fish lurk here too.
35:28 The barramundi, known in Australia as a delicious edible fish, is itself very good at getting
35:35 dinner.
35:36 Able to use its bucket-like mouth to suck prey in from over 20 centimetres away.
35:43 Perhaps the most skilful hunter though is the archerfish.
35:54 Living in mangrove swamps, rivers and streams, it doesn't look like much at first.
36:00 But it can do this.
36:07 This feat of marksmanship is even more impressive than it looks.
36:14 Archerfish can actively control everything about their jets.
36:18 Speed, angle, height and force.
36:25 Controlling a free jet of water like this is something that's challenging for humans.
36:32 But for the archerfish, it's all child's play.
36:35 If an insect is in range, to the archerfish, it's already history.
36:43 When the archerfish takes aim at an insect on an overhanging branch, its eyes are underwater.
36:50 Light bends when it enters water, so the fish must make a calculation about where the prey
37:04 really is and correct for the bending of the light.
37:09 Simple easy maths for the archerfish.
37:16 It must also adjust for gravity.
37:22 Water jets don't travel in a straight line because the force of gravity pulls them down,
37:27 changing their angle.
37:30 But the archerfish is able to work out this tricky physics problem too and compensate
37:35 for it.
37:42 Bullseye.
37:45 And researchers have discovered something about the archerfish that explains how it's
37:49 able to hit an insect with enough force to stun and dislodge it up to two metres away.
38:03 Most ballistic objects, like bullets, when shot upwards will slow down due to air resistance
38:09 and gravity.
38:11 But the water jet of the archerfish actually speeds up as it goes further.
38:18 As the fish lets fly with its jet, it modulates the stream so that the tail end of the jet
38:31 is moving faster than the leading end.
38:36 As the back end catches up with the front end, it combines into one big super blob that
38:42 moves even faster.
38:47 The energy that was dissipated over an arc is now condensed into a high-power ball of
38:52 water that blasts the unsuspecting insect from its perch.
38:59 Waterhole life is a complex web.
39:06 Distinctions between the hunter and the hunted are often unclear.
39:25 The whole ecosystem is in a delicate balance, but it works.
39:31 There is, however, something that's capable of not only throwing the system out, but completely
39:37 destroying it.
39:40 The cane toad.
39:47 Originally from Central and South America, cane toads were introduced to Australia in
39:52 the 1930s to try and control pest beetles in sugar cane crops.
39:59 But the toad has become a ticking time bomb for native species.
40:05 Its upper surface is covered in glands that exude highly poisonous toxins.
40:12 Many native animals eat frogs and toads as a natural part of their diet, so they unwittingly
40:19 eat the cane toads, a fatal mistake.
40:24 And that's not all.
40:27 If the toads happen to die near a water source, like the wetlands or waterholes, their bodies
40:32 will contaminate the water and kill any animal that comes to drink it.
40:39 Even cane toad tadpoles are poisonous.
40:45 They look virtually identical to harmless tadpoles, which are a vital food source for
40:50 many fish and birds.
40:57 These toxic toads are expanding their range westwards across the country at a steady pace
41:04 and are a complete disaster for native wildlife.
41:12 After three or four months of glorious, life-bringing rain, once again the seasons start to move
41:19 on.
41:29 By March, showers become lighter and more intermittent.
41:37 Little by little, the dry season returns.
41:44 As the dry season intensifies, the wetlands and waterholes begin to shrink back.
41:53 The water's edge turns to thick mud.
42:00 The once lush plant life begins to dry up.
42:07 Life for all the animals gets harder.
42:09 The migrants leave for wetter, fresher pastures.
42:16 But for the dingo, the shrinking water presents a new opportunity.
42:24 He's probably been searching the nearby wild country for prey.
42:29 Small mammals like rabbits or rodents are favourites.
42:37 As the centre of local animal life, the waterhole is also a prime spot to see if there's anything
42:43 to eat.
42:47 The dingo is an opportunistic feeder as well as an able hunter.
42:59 If something succumbs to starvation or disease, he'll take advantage of it.
43:06 He's a regular visitor to the waterhole, especially as the waters recede, leaving thick, cooling
43:15 mud behind.
43:21 As an apex predator, the dingo is good for the ecosystem.
43:27 It keeps down the numbers of feral cats, an introduced species which, along with the cane
43:32 toads, has wrought total havoc on native animals.
43:39 Today the dingo's just taking advantage of the facilities.
43:56 As the rainfall slackens off, for some species this is a time of plenty.
44:03 All the food concentrates into diminishing pools of water and becomes easier prey.
44:21 The extremes of a monsoonal climate in the far north have led to a boom or bust ecology.
44:28 Times of plenty followed by hard times.
44:36 The wildlife here has adapted to that.
44:43 Magpie geese switch from eating rice to eating high energy starchy tubers like water chestnuts
44:49 which they dig up with their hooked beaks.
44:54 Some of the frogs cocoon themselves in the mud, awaiting reactivation when the next rains
44:59 come.
45:05 The crocodiles start eating less as the seasons change and food becomes more scarce.
45:15 They too can dig themselves into the mud to rest through the dry.
45:22 The leaves of the water lilies will once more die off.
45:29 Some freshwater turtles wait for the dry season to lay their eggs in sandbanks.
45:40 Inside the eggs the embryos develop for around 70 days but then go into diapause, a state
45:47 of stasis.
45:50 In this dormant condition they wait until the next lot of heavy rain or flood water
45:55 reaches the nest.
45:58 Then all the hatchlings will burst out of the nest at once.
46:03 To avoid the worst of the drought, the jabiru will simply take off and fly to less ephemeral
46:09 water sources, as can the spoonbill and the rest of the birds.
46:15 The smaller life forms, like crustaceans, have their own ways of ensuring the next generation
46:21 lives through the dry.
46:23 Some have eggs that are resistant to drought and so tiny they can be born on the wind.
46:37 Wetlands and waterholes are a stunning microcosm of Australian biodiversity.
46:44 They're the natural storehouses for thousands of different species.
46:56 The magnificent jabiru.
47:05 The freshwater croc, both hunter and, in its youth, the hunted.
47:12 Aquatic sharpshooter, the archerfish.
47:16 Turtles and wading birds.
47:18 All take advantage of the limited time of abundance the wet season brings.
47:25 Playing their part in the vivid, interconnected life of the wetland and waterhole ecosystems.
47:32 [Music]
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47:47 [Music]
47:55 [Music]
48:02 you
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