The Trials of Life (1990) s01e03 Episode Script

A forest on the lower slopes of the Andes.
A spectacled bear is looking for a snack.
0ne of the problems that faces us and all animals is finding enough to eat.
Being animals and not plants, we only feed on other living organisms, and, by and large, other living organisms don't welcome that.
Animals run away or defend themselves, and even plants have surprisingly effective ways of preventing anyone from stealing their leaves.
I'm in the South American rainforest - the richest proliferation of life on Earth - so you might think that here I'd have no difficulty in finding food, particularly if I was prepared to be vegetarian.
But it's not as simple as that.
These woolly spider monkeys are taking their first meal of the day.
It might seem to be a gentle, peaceful scene, but, in fact, it's a battleground.
The tree defends itself by developing poison in its leaves, but when newly-sprouted, they're just edible, so the monkeys have to select which they eat with great care.
Even with great discrimination, they will swallow a little poison, and now they've had as much as they can tolerate.
They move off and find another kind of tree.
This too has poison in its leaves, but it's a slightly different kind, so the monkeys can take a second course of their meal, providing they continue to be careful.
Another drawback to eating leaves is that they're not very nutritious, and the monkey has to eat great quantities to sustain itself.
Huge meals require huge stomachs to hold them, and that means that the monkeys are not the most nimble of movers up in the branches.
After an hour or so of feeding, the need to digest their vast meals demands that they take time off and have a siesta.
Eating leaves is not easy.
The small red panda of the Himalayas is one of the few animals that has beaten the defences of the bamboo.
Its leaves are not only very fibrous but armed with tiny blades of silica, so sharp that they can cut flesh.
But the panda's digestion is able to cope with them and the reward is that it has all the bamboo it can eat, since so few other animals will touch it.
Bamboo also grows in Madagascar, and here the rare golden bamboo lemur feeds on it.
It scissors through the coarse outer leaves on the stem to reach the marginally softer and more succulent ones within.
Its preferred choice is not so much the leaves as the new shoots that come up through the ground like spears.
They, of course, are particularly important to the plant and it loads them with cyanide.
Eating one of these uncooked could kill a man.
The bamboo lemur can only eat them because its stomach produces special juices that neutralise the poison.
But developing this ability has a price - the bamboo lemur now can't eat much else.
So if the bamboo disappears, so does the lemur.
The greatest plunderers of leaves, however, are insects.
They're the most numerous creatures on Earth and a high proportion of them - as caterpillars or adults - eat leaves.
The evidence is everywhere.
Insects are also fussy feeders.
A female lays her eggs on the kind of plant her caterpillar's digestion can cope with, so when they hatch, they find the food they need immediately in front of them.
They are little more than eating machines - a pair of jaws attached to a bag-like gut.
No complications with wings and sex organs.
Those will come later when they turn into adults.
Now it's just munch, munch, munch.
Plague beetles have a special way of beating a plant's poison.
Since it's costly to produce, many plants only keep small stocks and deter grazers by rapidly deploying it to the point of attack.
But plague beetles descend on a plant in such numbers that its poison must be shared between many, and each beetle only gets a tiny and tolerable amount.
It's true that each one only gets a small meal, but as soon as they've finished with this plant, they move on to another.
The milkweed invests much more in its defences.
Its abundant and very poisonous sap - latex - is piped along special veins and is immediately available everywhere.
But this beetle has worked out how to deal with that.
It punctures the pipeline running along the leaf rib, so that the milky latex leaks out.
As a result, the poison never reaches the end of the leaf, and there the beetle can feed in safety.
The latex also seals a plant's wounds, because it rapidly solidifies in air.
But since it can't reach here, the beetle doesn't have any problem with gummed-up jaws.
Marmosets also deliberately wound plants.
They repeatedly gouge grooves in the trunks of trees that, when damaged, exude resin.
Like the milkweed's latex, resin seals off the tree's injuries, preventing loss of sap and the entry of infections.
But unlike latex, it's not poisonous.
0n the contrary, it's full of sugars and rather good to eat.
And the marmosets love it.
So the tree's measures to defend itself have actually resulted in encouraging its injury.
Not all plants are so uncooperative.
Some actually encourage animals to come and feed from them, and advertise the fact they've got food with brilliant displays, as these poppies are doing.
This is not, of course, generosity on their part, but self-interest.
The food they have to offer is a bribe to persuade the animals to act as couriers.
They need to have their pollen ferried across to other flowers.
Pollen in itself is edible.
Bumblebees have a great taste for it.
Bees have a complex arrangement of cones and brushes on their hind legs with which they gather pollen and pack it into baskets on their thighs.
As they move from flower to flower, the pollen that brushes onto their bodies on one flower brushes off on another, and the plant's purpose is accomplished.
Pollen, packed with genetic material, is a complex and expensive commodity, and many flowers offer a cheaper bribe - nothing more than sweetened water.
Nectar.
The plant produces it from nectaries usually in the heart of the flower, so that thirsty insects, to reach it, have to brush past the stamens, collecting a dusting of pollen.
In temperate lands, flowers can only be found in the spring and summer when there's no frost, so insects that shelter from the winter, in nests, have to build up stocks as quickly as they can.
They have, in fact, to be as busy as bees.
In the tropics, on the other hand, there are always plants of one kind or another in bloom, so it's possible to feed on nectar throughout the year, and many animals do.
This vine, combretum, is particularly generous.
Almost any animal that wants nectar can get it without difficulty when the plant is in flower.
Many birds which feed on fruit, berries, or even insects, come to drink from it.
And so do monkeys.
The smaller kinds - squirrel monkeys, tamarins and marmosets - can clamber right out onto the thinner branches.
Even the much bigger hefty capuchins, which feed on fruit, nestling birds, lizards and even, on occasion, small monkeys, enjoy a sweet drink.
As all the monkeys feed, so the stamens brush the fur on their face, and the pollen is on its way to another flower.
Nectar feeding has its problems.
A heliconia flower, like this one, produces only a little nectar at a time.
So if a hummingbird comes to feed from here, it has to go elsewhere to get more, so bringing about the heliconia's purpose of cross-pollination.
And it takes a little time for the heliconia to produce more nectar, so if the hummingbird comes back too soon it's wasted its journey; too late, and another bird may have stolen the nectar.
As a consequence, hummingbirds patrol a group of these plants, visiting each flower in strict rotation to an accurately timed schedule.
And he was right on time.
Hummingbirds are among the few animals that live almost entirely on nectar - they also eat small insects - and they've developed special equipment to collect it.
The wings have joints that enable them to beat with a whirling motion, giving perfect control in the air.
So it can hover in front of a flower and insert its beak with absolute precision.
The tongue is long and thread-like and flicks in and out thirteen times a second.
But this specialisation means that hummingbirds can feed on almost nothing else, and that puts them in the plant's power.
It may seem that this hummingbird is deciding which flower to drink from, but you could argue that the plant, by controlling nectar production, is dictating the movements of the hummingbird.
Many hummingbirds have a bill which, in its length and curvature, exactly matches the shape and dimensions of the particular flower on which they mostly feed.
The violet sabre-wing's beak fits into the columnea flower as accurately as a dagger slipping into a scabbard.
And the flower has stamens placed in precisely the position needed to put a dab of pollen on the bird's forehead.
So the sabre-wing and columnea have become partners.
This suits columnea because its pollen is not taken by hummingbirds feeding on other kinds of flowers, and so wasted.
And it suits the sabre-wing because, since no other bird has this shape of bill, it has all the columnea nectar to itself.
But not quite.
The mountain gem hummer has other ideas.
It's waiting for the flower's partner to leave.
Its bill is too short to reach the nectar as the sabre-wing does.
With a thrust from its wings, it tries to pierce the flower.
This time, it holds the flower with its feet.
It's broken in.
Columnea has been burgled.
Another thief, only too eager to take advantage of a flower.
Indian langur monkeys.
The flowers of the flame-of-the-forest are protected from raiders by being placed at the ends of long, thorny twigs, so they're reserved for their particular pollinators, birds.
But langurs find them very tempting.
This of course is disastrous for the tree.
Its complex, subtle mechanisms for getting its seeds fertilised, evolved over millions of years, are being chewed to pieces.
Even the remotest flowers aren't safe, for the young babies, braving the thorns, can clamber right out onto the thinnest branches without them breaking.
In the continuous struggle between animals and plants, this round has certainly been lost by the plant.
In the lush forests of the tropics, where flowers bloom all year, animals that feed on nectar can always find a drink somewhere.
But in other parts of the world, where the winters are bitterly cold, or here in the deserts of Australia, where flowers only bloom after brief rains, animals that rely on nectar have to have some way of storing it to last them through the hard times.
These mulga trees produce nectar on which ants feed, and they have the most extraordinary larders.
The galleries of their nests lie four feet or so below the surface of the ground.
These golden globes hanging from the roof are their storage pots, full of honey.
Each one is alive - an ant with an abdomen expanded to the size of a grape.
The small dark flecks are the hard plates which protect the body of a normal-sized ant.
It's the membrane between them that has stretched.
These bloated individuals are almost totally inactive, so they consume little of the honey that they hold.
It is drunk by the busy workers who, when there's little food above ground, come down here and induce the honeypots to regurgitate it.
The workers also tend the swollen bodies, keeping them well-groomed and clean.
During good times, the workers collect all the nectar they can and take it down to the larders to top up the colony's storage jars by feeding it to them drop by drop.
The people who have roamed these deserts for millennia - Aborigines - have always valued these ants as one of their few sources of sugar, and they eat them just as they are.
Mmmm.
Mmmm.
It's liquid, warm, and marvellously sweet.
A few weeks after flowering, many plants tempt animals with another food - fruit.
They have another problem.
Their seeds are formed and need to be distributed.
By wrapping them in sweet edible pulp, they recruit lots of animals to do the job.
The trees dissuade animals from collecting the fruit before the seeds are fully developed by not producing the sugars in it until the last moment.
So unripe fruit tastes bitter and is really not worth picking.
To indicate when it is, the fruit often changes colour.
Squirrel monkeys are primarily fruit eaters.
They move about in large groups of 40 or so, and must wander over a great area to find all the fruit they need.
Capuchins, on the other hand, live in small families, each with its own patch of forest.
They eat all kinds of things, but if there's fruit in their territory, they'll know about it.
So although the squirrel monkeys are frightened of the bigger capuchins, they still follow them as they forage.
There may be something for the capuchin - a lizard maybe - but no fruit.
So the squirrel monkey is not interested and must wait.
The capuchin moves on.
And the squirrel monkeys follow.
As the capuchins get near the fruiting tree, the squirrel monkeys, perhaps smelling the fruit, scamper ahead to try and get to it before the more powerful capuchins reach it and drive them off.
Now they must grab as much as they can as quickly as they can.
The capuchins arrive.
It's time for the squirrel monkeys to go.
They take with them, inside their stomachs, the tree's seeds.
They pass through the monkeys and then, some distance away, they're deposited with a convenient dollop of fertiliser.
Seeds themselves are packed with nourishment, so plants enclose them in shells which can be strong enough to defeat even a mangabey.
Victory to the plant.
But the chimp is so clever, it can crack them.
Victory to the animal.
Sharp teeth enable an agouti to chisel into the acorn of a tropical oak.
In spite of the acorn's armour, it seems that the oak has lost this contest.
But not totally.
The oak produces more acorns than the agouti can eat immediately.
Those that it can't, it carries away and buries for later.
But an agouti's memory is not infallible.
0ccasionally, it will forget about an acorn, which may germinate and grow into a new oak.
That will be a victory for the plant.
Perhaps the most extraordinary of all tools for nut eating is wielded by a strange Madagascan lemur, the aye-aye.
First it gnaws a hole, then scoops out the contents with this long bony probe, which is, in fact, its finger, but one quite unlike its others.
This curious digit serves just as well for eating a grub.
The aye-aye uses it to mash up the body in its burrow, and then flicks out the purée.
The spiny pocket mouse has a double problem.
The seed it's gnawing is not only hard-shelled but packed with poison.
The mouse does nothing more than puncture the shell.
It then tucks it into its cheek and carries it back to its burrow.
The hole in the shell stimulates the seed to germinate, and the tender white shoot that leaves the protection of the shell is poison-free.
The macaw has, almost certainly, the most powerful nutcracker of all.
It can demolish even the most resistant of nuts.
Many of the seeds macaws eat are also filled with poison, yet this doesn't seem to upset them.
How do they survive? Every day, they make long journeys through the forest to dose themselves with a special antidote.
Macaws usually fly in pairs.
0nly in such places as this do they assemble in flocks.
They've come to collect their medicine.
The regular presence of so many birds attracts eagles and other predators, so before the macaws come out of the trees, they want to be sure that it's safe to do so.
They wait for one bird, braver than the rest, to make the first move.
There it goes.
And this is what they're after.
Kaolin.
The soil in this river bank is rich in it.
Several kinds of parrots and macaws come here every day from miles around to take the treatment.
Kaolin combats acidity in the stomach, absorbs and neutralises poisons.
As a bonus, this clay is rich in calcium and sodium, which is lacking in diets that consist of fruit and nuts.
So eating plants poses more problems than one might think.
But eating other animals, even small defenceless ones, also has its difficulties.
It's dawn on the east coast of England, the middle of winter and food is very scarce.
But behind me is a huge and abundantly stocked larder.
Its doors have been shut for the past three hours, but now the tide is on the turn, and for a horde of hungry animals, their waiting is almost over.
Tens of thousands of knot and dunlin have assembled on a lagoon on the other side of the sand dunes.
They've sensed that the tide has exposed a mudbank.
Breakfast is served.
Millions of tiny molluscs are buried just below the surface of this mud and the birds are feeling for them with their bills.
Abundant though the food is out there, collecting it is a very dangerous business.
It's very exposed on the mudflats - there's nowhere to hide, nothing to dodge behind, and the birds deal with that problem by sticking together in tight flocks.
That way, each bird has a thousand eyes ready to spot danger.
But if that is such a good idea, why is this redshank out on its own? It's hunting, not by touch, but by sight, and it's searching for its favourite food - small shrimp-like crustaceans.
If they are alarmed by ripples or vibrations produced by many moving feet, they will disappear into the mud where the redshank can't see them, and so can't find them.
So if a redshank wants to catch this more swiftly-moving food, it has to forage by itself, despite the risks.
And if it does become a little alarmed, it just squats.
Some waters are so rich in food, there's plenty for everybody.
0n this Indian lagoon, there are storks, herons and egrets, openbills and spoonbills.
Each has its own particular beak technique with which to catch its favoured prey - probing and sieving, scything and stabbing.
Even parts of the open sea, like this bay in the West Indies, at certain times become so thick with fish that they can support great flocks of fishermen.
Barracuda - among the most ferocious hunters in the sea.
They regularly drive shoals of small fish into the bay.
(SCREECHING) The pelicans can tackle the shoals even when they're a foot or two beneath the surface.
But a pelican can only swallow the fish it's scooped up in its bill if it lets the water drain out first.
To do that, it must open its beak slightly, and that is the moment the gulls are waiting for.
Few places on land offer quite the density and richness of animal food that can be found in parts of the sea such as this.
But one kind of land animal does swarm in vast numbers, and this little long-eared tenrec from Madagascar is in search of them.
They can be sniffed for, but the tenrec's huge ears also help to locate them, for they make a faint rustling noise as they scurry along their pathways.
Termites.
The juicy, soft-bodied workers are largely defenceless.
But with them come soldiers.
This kind squirt noxious chemical sprays from nozzles on their heads.
The tenrec, with its sensitive nose, can tolerate a certain amount of chemical spray, but after a while it just has to come up for air.
Termites are hugely abundant in the tropics, and many different kinds of animals collect them when they get the chance.
A small gecko in the deserts of Australia eats little else.
The problem is those soldiers.
But it is such a fastidious and accurate feeder, it can avoid them and pick out the defenceless workers one by one.
0f all food-collecting devices, the most ingenious and elegant must be the webs of orb spiders.
It's nearly always the females who build them.
0ne starts by rigging filaments of silk across a flyway used by insects.
Around the spokes, using silk of a different kind, she sets a spiral mesh.
As she secures each section, she twangs it, so that the glue with which it's coated breaks up into a line of sticky beads.
0ne of the biggest of these webs, which may be two yards across, is constructed by the nephila spider.
She is huge.
Her legs can span six inches and she's virtually blind.
A fly blundering into her web is quickly seized.
She rapidly injects it with a venom that will liquefy the contents of its body.
She then wraps it up in silk and parks it on the web to allow the venom to take effect.
But nephila is not alone on her web.
Argyrodes is tiny, much smaller even than the fly.
She could easily become a meal for nephila.
She too is blind, but she's also felt the vibrations of the fly.
With what seems like suicidal recklessness, she approaches nephila, still feasting on her prey.
And she too begins to eat food that nephila not only caught, but has conveniently pre-digested.
Another capture calls nephila away.
0nce again, she stabs the fly, trusses it up and carries it away to hang on the side of the web.
She'll eat that later.
Argyrodes seems well aware of what's going on.
As soon as nephila has hung up her latest catch, argyrodes starts trying to discover its position by pulling the web filaments.
Nephila has returned to finish her first meal.
Meanwhile, argyrodes has run a line from the top of the web to the fly, which she's now cutting loose.
0nce the fly is free of the web, she lowers it down.
The stolen fly is now hanging entirely free.
Nephila won't be able to reclaim it now, but argyrodes must get it to a place where she can feed on it in safety.
Step by step, she heaves it up.
Her theft is complete.
Tropic birds nest on this cliff in Tobago in the West Indies.
They're magnificent fliers, able to exploit all the currents of the air with spectacular ease.
They fish out at sea, and every day the hard-working parents return to their nests with crops full of food for the family.
18th-century frigates were swift, heavily-armed warships which plundered merchantmen.
These are frigate birds.
The fishing fleet is returning.
The frigate wasn't trying to kill the tropic bird, only to make it surrender its cargo of fish.
But it'll have to find a less determined victim.
The usual tactic is to come up astern of the chosen victim and grab its leg or tail.
It surrenders.
There goes the disgorged fish, and the frigate catches it.
The frigates aren't always successful.
Watching them, you can't help wondering if it wouldn't be easier to catch the fish themselves, and indeed they often do.
But they seem positively to enjoy a life of piracy.
As to the tropic birds, most of them escape, and those that are caught only lose a few fish.
But it's only a short step between robbing your victim and killing him, for the pirate to become a hunter.
And that raises a completely new set of problems.
It's those that we'll be looking at in the next programme.