BBC Wild South America_2of6_Mighty Amazon
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00:30The Amazon is the mightiest river on earth. A thousand miles before it reaches the sea,
00:43its main channel is already ten miles wide. By the time it meets the ocean, it carries
00:50a fifth of all the river water in the world, spilling an incredible 45 million gallons
00:56a second into the Atlantic. Every year without fail, the Amazon bursts its banks and floods
01:12an area of forest the size of England.
01:27This huge change in water level over such a vast area affects everything that lives
01:35here in a dramatic way.
01:43Over its 4,000 mile course from the Andes to the Atlantic, the Amazon is swollen by
01:57some 1,100 tributaries. Several are massive rivers in their own right. Between them they
02:04drain 40% of the continent. 3,000 kinds of fish live in this water world.
02:12And where there are fish, there are fish hunters.
02:43Giant otters. They really are giants, nearly two metres from nose to tail. Local people
02:53call them lobos del rÃo, wolves of the river. They live almost entirely on fish, though
03:01they can kill caiman and anacondas. They're one of the top predators of the Amazon, the
03:07aquatic equivalent of the jaguar.
03:17Most otters are solitary, but these are very sociable. They live in family groups of about
03:23half a dozen, a mated pair and their full-grown young from previous years.
03:30The otters bridge two worlds. All their food comes from the river, but they sleep and rear
03:35their cubs on dry land. So their lives are profoundly affected by the changing level
03:42of the river, which has its origins far to the west in the distant peaks of the Andes.
03:49After a first precipitous rush from the mountains, the river's course is flat and winding. For
03:56the next three-and-a-half thousand miles, it drops barely two inches a mile. As sluggish
04:15meanders twist across the floodplain, their course is constantly changing, creating new
04:20channels and lakes. This is more than just a river. It's a whole river system.
04:37It's October, the height of the dry season. The Amazon is at its lowest ebb and showing
04:45its bare bones. For just a few weeks each year, sandbanks rise clear of the water, giving
04:55a brief window of opportunity for one of the Amazon's most remarkable animals.
05:14Giant river turtles. They're one of the largest freshwater turtles in the world, over a metre
05:22long and weighing more than 40 kilos. They come back to the same place each year to lay
05:30their eggs, but this is a race against time because the sandbanks will soon be flooded
05:36again.
05:45For two weeks after they arrive, the pregnant females bask in the sun. This hastens the
05:57development of the eggs still inside their bodies. When she's ready, each huge female
06:05digs a hole a metre deep. In it she'll lay a hundred soft-shelled eggs. But all this
06:15activity doesn't go unnoticed. Good sandbanks are few and far between, so early clutches
06:25of eggs are often accidentally dug up by turtles nesting later.
06:35For the vultures, too, this is a once-a-year opportunity.
06:44But it only lasts a few days. The turtles will soon be gone.
07:05In 45 days, the surviving eggs will hatch, far quicker than other turtles.
07:12Just a week or two later, the sandbanks will be drowned again. If the rivers rise early,
07:19all the eggs are lost.
07:24The turtles will soon be gone.
07:29In 45 days, the surviving eggs will hatch, far quicker than other turtles.
07:36If the rivers rise early, all the eggs are lost.
07:45At the peak of the dry season, broad reaches of river can be almost cut off as sandbars
07:52separate them from the main flow.
07:59Fish become concentrated in these lagoons, so for predators the killing is easy.
08:06Caiman and egrets gather to take advantage of the best hunting of the year.
08:19The fish take shelter in the reeds, but in shallow water they're easier to catch.
08:29Striking low and from the side makes it harder for the egrets' prey to see them, until it's too late.
08:41Sometimes the caiman seem to work together to herd fish into the shallows.
08:49The shoals of prey become even more concentrated.
09:08The water literally heaves with fish.
09:18With so many to choose from, there's no need to single out a target.
09:23A random lunge can be just as effective.
09:26And as each caiman strikes, it panics fish into the jaws of another.
09:35But the good times won't last long. The caiman must make the most of them while they can.
09:48A feast like this could keep them going for months.
10:19For most fish, the dry season is not a good time.
10:25They're on everyone's menu, and their own food's so scarce that many will not eat for months.
10:38Some of the birds are having a hard time too.
10:42Tui parakeets are seed eaters, and the seeds of this munguba tree are a rare treat.
10:52The munguba uses the wind to scatter its seeds.
10:57Each one is carried on a parachute of fluff.
11:00But if it lands on the water, there's not much chance of it germinating.
11:07These are bricon, sometimes called South American trout.
11:18They're so hungry, they jump at the chance of even these meager mouthfuls.
11:36They can leap up to four times their body length.
12:07Even at low water, the larger rivers are still navigable.
12:13On the Amazon's main channel, seagoing ships can reach as far as the city of Iquitos, over 2,000 miles from the ocean.
12:26The rivers are the main arteries of travel. Local people depend on them throughout the year.
12:37Riverside communities rely heavily on fish for their livelihood.
12:43For the people, as for the natural predators, low water is also the best time to make a catch.
13:06Laden with silt from the distant mountains, the rivers are often very muddy.
13:12It's hard to see much underwater during the day. At night, the problem is even worse.
13:18Infrared cameras let us follow the action in total darkness. But how do the fish find their way?
13:28Some, like these candiru, have an acute sense of smell.
13:33They can detect the slightest trace of blood or decay.
13:41Fish trapped in fishermen's nets are easy meat.
13:45Like aquatic vultures, the candiru home in on the scent of flesh and strip the carcass from within.
13:54A close relative of these candiru has the most unsavoury reputation of any fish in the Amazon.
14:00It's a parasite rather than a scavenger, and it's attracted to blood and urine.
14:06It's been known to swim right up into people's bodies, wedging itself inside with backward-pointing spines.
14:23Other fish deploy much stranger senses, ones that we can scarcely begin to visualise.
14:38They generate an electric field around their body. Any object in their path distorts the field.
14:45They detect the changes with receptors in their skin.
14:50This extraordinary sense allows them to find their way around in the murkiest of water, and to detect and catch their prey.
15:04They also use it to communicate.
15:12Most electric fish generate a very weak field, but not this one.
15:19To local people, it's one of the most feared fish in the Amazon, the electric eel.
15:30Its two-metre-long body is a gigantic battery.
15:34It can deliver a jolt of 600 volts, a shocking defence, enough to kill a child, and more than enough to stun its prey.
15:50As the rivers shrink to their very lowest, some of the channels are entirely cut off.
15:56Here, predators and prey become even more concentrated.
16:04Territorial male caiman have put aside their differences to take advantage of the glut of food.
16:10But in such cramped conditions, disputes are inevitable.
16:20Despite the crowds, there are still plenty of fish to go around.
16:28But that doesn't remove the temptation to steal someone else's.
16:50Even theft is scarcely worth the energy.
16:53The heron keeps its meal.
16:58For fish hunters, these are the good times, though not without a price.
17:03The heron is the most expensive fish in the world.
17:06It's the most expensive fish in the world.
17:09It's the most expensive fish in the world.
17:12It's the most expensive fish in the world.
17:15For fish hunters, these are the good times, though not without their annoyances.
17:21Caiman may look armour-plated, but there are chinks in their defences.
17:29With only their heads out of water, they're still a target for blood-sucking horseflies.
17:37Even a harmless butterfly can be a nuisance.
17:46The first showers hint at a change of season,
17:49a promise of rising water and better times to come
17:53for fish now trapped at the mercy of predators like caiman and egret.
18:06For the cormorants, too, the best of the fishing will soon be over.
18:11Released from their dry-season prison, the fish will spread out and become harder to catch.
18:16They'll be too scattered to feed a flock like this.
18:20The dry season may be coming to an end, but not just yet.
18:28Fish will not settle in their flocks now.
18:32The dry season may be coming to an end, but not just yet.
18:50This is only an isolated shower, it will take much more to set the fish free.
19:00The first rain can even make things worse for them, much worse.
19:05The cold rainwater sinks, displacing warmer and less oxygenated water below.
19:16Decaying vegetation and bubbles of hydrogen sulphide rise from the depths.
19:22This lethal cocktail makes oxygen levels plummet, and fish are soon gasping for breath.
19:31The topmost film of water, where it touches the air, still has the most oxygen, so desperate
19:36fish skim the surface to avoid suffocation.
19:51Most kinds of fish seem to be affected.
20:05For the birds, this may be the last opportunity to make a killing.
20:20The distressed fish are easy prey for the cormorants and egrets.
20:33With so much on the menu, they ignore the dead and dying.
20:37But not all of these will go to waste.
20:44For the vultures, this is another brief window of opportunity.
20:49Fish kills are sudden and short-lived, and the dead fish soon sink.
20:55Black vultures have an acute sense of smell.
20:58The stench of rotting fish draws them to the feast in increasing numbers.
21:25There is too much, even for the vultures.
21:27The victims of this natural disaster can number tens of thousands.
21:45Isolated local showers turn to more general rain.
21:54The Amazon basin gets a massive three metres of rain a year, most of it concentrated in
22:01just a few months.
22:06The timing of the rainy season varies from one part of this vast catchment to another,
22:11but the result is the same everywhere, a slow but inexorable rise in the river level.
22:22The changing season has a profound effect on everything that lives here.
22:27Swollen by the rain that falls within the basin, the rivers are soon full to the brim.
22:40But there's more to come.
22:46In the cloud forests of the Andes, the annual rainfall can be an incredible six metres.
23:00When that joins with snowmelt from the high peaks, the results are dramatic.
23:17It may be days or even weeks before these torrents make their full impact on the floodplain
23:40forest hundreds of miles to the east, but already animals are on the move.
23:54The rain that has already fallen here waterlogs the soil and raises the humidity, and that
24:00triggers a remarkable migration.
24:10The small creatures of the leaf litter move upwards into the trees.
24:16Soon their world will be transformed.
24:28Caught up in the treetops, predators are waiting for them.
24:58For many of the leaf litter animals, the shift to the treetops proves fatal.
25:12So why do they move?
25:21It can take two months, but finally the rain and snowmelt from the Andes make their mark.
25:28The rivers are already full from rain in the lowlands and can take no more.
25:32Now they overflow into the forest.
25:39The reason for that mass migration from the leaf litter becomes clear.
25:43The forest floods to a depth of ten metres.
25:49The flood changes the lives of everything that lives here.
25:54Even the giant otters are on the move.
25:57Their dry season dens are now under water, so they have to move their young to higher
26:01ground.
26:04This year's cubs are still too small to swim far, so the adults carry them in their jaws.
26:27Giant otters are territorial, and the group's range has to include dens for both low and
26:31high water.
26:51The whole family share the task of looking after the young.
26:56It will be two or three years before their elder brothers and sisters leave to start
27:00a family of their own.
27:10Few predators will tackle a full-grown giant otter, but infants can be killed, especially
27:16by caiman.
27:40Safely installed in their new home, the otters will stay here until the flood water recedes.
27:53At the height of the flood, Amazonia is transformed.
27:58An entirely new habitat has been created, a water world that can drown the forest for
28:03ten miles either side of the main river channel.
28:17At the peak of this inundation, the rivers engulf an incredible 57,000 square miles of
28:24forest, an area the size of England.
28:31The trees can stand in water for six months or more, but this drowning is something that
28:37happens every year, and many will turn the flood to their advantage.
28:51Branches where birds once perched now shelter fish.
28:56Feed from the dry season confines of the riverbed, they spread out into the forest.
29:02This is their season of plenty.
29:16Predators follow the fish into the forest, but now it's much harder for them to hunt.
29:21Their prey are more scattered and have more places to hide.
29:27The hunters include one of the Amazon's most remarkable animals, the Botodolphin.
29:38This river dolphin is almost blind, but the water here is often so muddy that eyes are
29:43useless.
29:44It finds its way through the branches by using sonar.
29:49Like its marine relatives, it has a very flexible neck, so it can sweep its head from side to
29:54side to scan the water ahead.
29:58And to catch fish.
30:20Because there is so much decaying vegetation, the water in the flooded forest is very low
30:24in oxygen.
30:28That's no problem for an air-breathing dolphin, but how do fish survive here?
30:36The Pirarucu is the largest freshwater fish in the world.
30:41It can grow to three meters and weigh nearly 150 kilos.
30:49Like the dolphin, this giant has to breathe air.
30:56Every few minutes it comes to the surface and takes a gulp of oxygen.
31:02All sorts of other fish share this ability.
31:08The electric eel absorbs oxygen through the lining of its mouth.
31:14It acts like a lung.
31:19Many of the Amazon's fish have a high concentration of red blood cells, which makes their gills
31:23more effective, but they also take air from the surface.
31:34A swamp eel traps great gulps of air in its inflated throat.
31:46Animals that live in the trees also need special skills to survive in the flooded forest, like
31:51being able to swim.
32:03Sloth and spider may seem unlikely swimmers, but their own form of freestyle is now the
32:09best way for them to move between trees.
32:26If you can't swim, climb or fly, you can't stay here.
32:31So this water world has none of the usual forest animals, like deer or peccaries.
32:43The sloth may not be fast, but it's a good swimmer and climber.
32:59The most unexpected creatures take to the water.
33:06Fire ants even turn the flood to their advantage.
33:11When their forest floor nests are drowned, they set sail on a living raft, formed from
33:16their own interlinked bodies.
33:26Drifting with the current, they can end up far away from their old home.
33:32All they need for a new colony is on the raft, including the next generation.
33:42But the voyage has its hazards.
33:46Fire ants have a painful sting, but that doesn't stop fish picking them off as they drift through
33:50the forest.
34:08Eventually the rafting ants make landfall.
34:13This tree will provide a refuge until the waters fall, and they can return once more
34:18to the forest floor.
34:25If their eggs are to survive, they must find shelter from the drying heat of the sun.
34:39A crack in the bark is a perfect nest site.
34:45The tree comes with a built-in food supply.
34:49Others have already taken refuge here.
34:51They arrived even before the flood had started.
35:01The lizard has now got competition.
35:15These insects are all on the fire ant menu, but they seem strangely reluctant to jump.
35:26Those that do take the plunge may find that they've leapt from the frying pan into the
36:01Fish are quick to take advantage of any insects that fall into the water.
36:09For some, like the meter-long arowana, they're a large part of their diet.
36:19The fish may not have eaten for months, so now it's time to fatten up.
36:28Wind and rain dislodge a steady supply of insects from the crowded canopy above.
36:40Even if it's not actually in the water, an insect still may not be safe.
36:52All sorts of other fish make the most of the windfalls.
36:57Needlefish cruise the surface, picking off anything small.
37:05Like some other fish in the Amazon, and the dolphins, these little fish have a marine
37:09origin.
37:13They spend most of their time near the water's surface, hunting by sight.
37:18That slim profile may help to camouflage them.
37:32Their long beak is ideal for seizing prey.
37:40The rising water triggers an event that will affect the lives of almost everything that
37:45lives here.
37:58It's now that the trees in the flooded forest fruit.
38:17Many trees depend on the flood to disperse their seeds.
38:21By the time they germinate, the water will have carried them far away from their parentry.
38:27Drifting with the flow isn't the only way seeds can travel.
38:34In this strange new world, some trees use fish to scatter their seed.
38:42The fish eat the fleshy part of the fruit, but the hard seeds pass through their gut
38:46unharmed.
38:47This is a good time for fish.
39:04They gather wherever fruit falls, and where there are fish, there are fishers.
39:26Most of the predatory birds have gone, but not this one, a little green heron.
39:49Most fruit eaters have an equal partnership with the trees.
39:52They spread their seeds in return for food.
40:00But some fish don't play by the rules.
40:04They eat the seeds, crunching them up and destroying rather than dispersing them.
40:11Tambaqui have a powerful sense of smell to lead them to fruiting trees.
40:23They have powerful jaws too, well able to crush hard seeds such as this walnut-like
40:28supacayu.
40:31Little of what they eat will ever get the chance to germinate.
40:51The flood is also a good time for the wakari.
40:58These monkeys live in loose groups of 30 to 50.
41:05They seldom come down to the ground, preferring to travel through the treetops in elegant
41:10leaps and bounds.
41:11So when the forest floods, they have no need to swim.
41:22These bizarre monkeys live only in floodplain forests, where they take full advantage of
41:27the flush of new fruit.
41:55Some people call this the English monkey.
41:58Its red face reminds them of a gin-swilling white man who's been out too long in the sun.
42:03In fact, the red face is a sexual signal, a sign of potency and good health.
42:13Wakaris are one of the few monkeys that live in this riverine forest all year round, surviving
42:18on leaves and unripe fruit.
42:21With their strong jaws, they can tackle food that would be too tough for other animals.
42:33The seasonal flooding of the forest leaves nothing untouched.
42:37Everything that lives here has to adapt or move on.
42:41Remarkably, people stay here right through the year.
42:45Their houses are built on stilts or rafts to raise them above the flood, as are their
42:50chicken coops.
43:07Watering the plants may be easy, but a floating platform is now the only place to grow vegetables.
43:14This is a challenging time.
43:16Most people depend on fish, but the shoals of the dry season are scattered through the
43:21forest and so harder to catch.
43:28All sorts of predator are having a hard time.
43:32Even fearsome hunters like piranhas are reduced to scavenging for scraps.
43:41Of all the Amazon's fish, these have the most notorious reputation.
43:47They could strip a chicken to the bone in seconds if it were careless enough to fall
43:52in.
44:08Swimming on the water does have some advantages, at least for children, though most of us wouldn't
44:13want piranhas in our swimming pool.
44:16In fact, their ferocious reputation is undeserved.
44:23Only in the dry season, when they're concentrated in landlocked pools, are they truly dangerous.
44:30So for now, it's safe to swim.
45:00People can live without dry land, at least for a while.
45:29But otters can't.
45:31They need a dry den to sleep in and rear their young.
45:36They're now deep in the flooded forest, well away from the open river, hunting fish hidden
45:42in the trees.
45:46The easy times of the dry season may have gone, but otters are supreme predators.
45:59Their webbed feet and paddle-like tails, their strength and agility make them a match for
46:04even the most elusive fish.
46:28If fish are hard-pressed to escape an otter hunting alone, they're even less able to get
46:43away when they hunt as a pack.
46:51Often the whole family fishes together, driving their prey into a tight shoal or trapping
46:56them against a bank.
47:06The rewards of communal fishing are one of the most important benefits of family life.
47:20Over the months to come, the floodwater will slowly drain from the forest.
47:24The rivers will once again be confined to their channels, and the otters will return
47:29to their dry-season dens.
47:37Giant otters are an indicator of a healthy river.
47:41Only where they have a plentiful supply of fish and can live undisturbed do they survive.
47:54There are many threats to the world's last wild places, but the sheer scale of the Amazon
47:59could be its salvation.
48:01It's far too mighty to control, dam or divert.
48:08The massive yearly flood makes it a hostile home for all but a few people, and means this
48:14watery wilderness may always remain untamed.