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The natural world is full of extraordinary animals
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with amazing life histories.
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Yet certain stories are more intriguing than most.
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The mysteries of a butterfly's life cycle,
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or the strange biology of the emperor penguin.
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Some of these creatures
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were surrounded by myth and misunderstandings
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for a very long time.
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And some have only recently revealed their secrets.
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These are the animals that stand out from the crowd.
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The curiosities I find most fascinating of all.
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Animals are usually either male or female.
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And, usually, they behave in a way
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that is characteristic of their gender.
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But in nature, there are always curious exceptions.
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Female hyenas behave and look like males.
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And male seahorses play mother
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and physically give birth.
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Only now are we beginning to understand
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why these two animals seem to have swapped their sexual identities.
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And also in this programme,
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spiders spin intricate webs using their own silk.
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And birds weave nests from strips of leaves.
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I investigate the skill of these spinners and weavers
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and the way they use such materials
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to produce such truly complex structures.
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Seahorses are fascinating.
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Some are tiny and blend perfectly with their surroundings.
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Others could grow to an impressive 35 centimetres in size.
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They live in shallow waters, both tropical and temperate,
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across much of the world,
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and have even been found in the Thames Estuary near London.
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Seeing one for the first time is a moment to remember.
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They're magical creatures, with a truly fantastic appearance.
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They have the head of a horse, eyes like a chameleon,
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the prehensile tail of a monkey,
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armour that can change colour
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and, perhaps most strangely of all, a pouch.
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Their unusual features inspired their name, Hippocampus,
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a combination of two Greek words -
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hippo, meaning "horse", and kampos, meaning "sea monster".
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For centuries, they've been considered
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animals of myth and legend,
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and only today are we unravelling the true story
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of males that give birth.
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Seahorses baffled early naturalists.
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Their unusual characteristics seemed to make them misfits.
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But after much debate,
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they were recognised as true bony fish.
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But their breeding habits were hardly fishy.
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Typically, female fish release large numbers of eggs into the sea
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that males must quickly fertilise.
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But a fish that kept its eggs in a pouch seemed scarcely believable.
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The seahorse's striking appearance
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has given it an almost magical status.
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Images and stories of a creature, part horse, part fish,
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have spanned the centuries across many cultures.
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Among the most famous are those belonging to Poseidon.
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This famous Greek god of the sea
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lived below the waves,
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and his golden chariot was pulled by a pair of giant hippocampi.
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The seahorse's odd behaviour appeared mysterious, too.
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As early as the third century BC,
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Aristotle noted in his book on the history of animals
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that pipefish, close relatives of the seahorse,
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had a pouch that burst into two
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to release the young.
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These early observations
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of the pipefish's strange breeding behaviour
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help to reveal the true story
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of the male seahorse's mysterious pouch.
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Just like seahorses, pipefish carry their eggs around with them.
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Some species simply stick the eggs to the outside of their bodies.
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Others have a rudimentary pouch.
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These simpler techniques provide some clues
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as to how seahorses developed their more complex closed pouch.
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But what Aristotle didn't know
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when he spotted the pipefish giving birth,
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was that he was actually looking at a male.
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And this important detail
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was to remain undiscovered for hundreds of years.
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Although seahorses live in British waters,
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until Victorian times few people apart from fishermen
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had ever seen them.
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In 1859, a Mr Pinto brought four live seahorses back to London
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from the mouth of the River Tagus in Portugal.
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Pinto endured a sleepless seven-day train journey through Europe,
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waking himself frequently
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to aerate the seahorse's water with a syringe.
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His seahorses survived
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and were installed in the new London Aquarium.
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They were an instant hit.
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Seahorses were headline news.
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Mr Pinto's journey and their arrival made the front pages.
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Now they could be seen in great detail,
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and the study of their mysterious breeding began.
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In that same year,
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what was described as a "herd" of baby seahorses
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was born in the British Midlands Aquarium.
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This caused quite a stir, as did the discovery
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that it was the male that gave birth to the young.
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But why seahorses swapped parenting roles remained a mystery,
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and we're still searching for the answers today.
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Here at the London Zoo's aquarium,
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over 150 years since the arrival of the first seahorses,
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a detailed study is revealing more about their reproduction
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and the usual role of the male.
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These tanks are set like a seahorse dating centre,
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the first port of call
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is the courtship aquarium, or ballroom tank.
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Here, a number of adult seahorses
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spend time getting to know each other
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as they look for compatible partners.
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Breeding seahorses form lasting partnerships as mating pairs,
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and their long, elaborate courtship dances
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are a way of finding and securing a suitable mate.
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Dances like those of this Australian species
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can be complex and last several days.
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They help the couple synchronise their bodies
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so that the male's pouch is ready for the eggs.
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They also help to establish the couple's joint territory.
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Seahorses were thought to be monogamous,
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but we now know that some are only exclusive couples
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for the duration of the breeding season.
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The female must choose the right male
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because she's going to pass over her precious eggs to him.
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Female seahorses do not have a pouch,
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so a strong pair-bond with a male is very important,
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as he will care for her eggs.
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This is the honeymoon tank.
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Seahorses that have shown an attraction for each other
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in the courtship tank
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are removed as a couple
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and given their own private space.
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In the wild, each pair has its own territory
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and these smaller tanks make captive breeding more successful.
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Here, the pair can synchronise their courtship.
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Timing is crucial.
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The female's eggs must be fully developed
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at exactly the same time
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that the male's pouch is ready to receive them.
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Once the female's eggs are ready,
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she hydrates them with seawater.
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They must then be laid within 24 hours.
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She transfers her eggs to her partner
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by inserting her egg-laying tube, or ovipositor,
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into the male's pouch.
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Once pregnant, the male attaches himself to one spot
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and the female visits him every day.
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She checks to see when he'll be ready for her next batch of eggs.
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One theory suggests that because the male is incubating the eggs,
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the female has more time to feed
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and can put energy into making new eggs more quickly.
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Swapping roles may be a smart way
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to use their resources more efficiently.
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What goes on inside the pouch is still a mystery.
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The male may simply provide a closed incubator.
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Or the inner skin may develop extra blood vessels
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to give a more placenta-like connection.
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It's not clear.
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During pregnancy and birth
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the male's metabolism increases,
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but that's little wonder,
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for he may have up to 1,500 eggs in his pouch.
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The male seahorse gives birth to dozens of miniature babies,
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perfect in every detail.
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The free-swimming young are put into separate creche tanks
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where they can be fed and cared for.
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The parent seahorses in this biological hotel
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remain in the honeymoon suite
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ready to mate again.
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These are some of last year's youngsters
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and they've grown enormously.
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Next year, they'll be breeding themselves.
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Swapping the parental roles
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seems to work well for seahorses.
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In warm conditions, a male can give birth every 28-30 days.
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But of the thousands of fry produced each year, only a few survive.
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There is no safe creche in the open sea.
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To succeed, seahorse parents must work well together,
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yet in this partnership,
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the female seems to have the freedom
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to swim, feed, and patrol the territory,
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which is normally the prerogative of the male.
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So, is the male seahorse a slave to a gallivanting female?
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Well, latest research suggests not,
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and shows that some males may have more control over breeding
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than first thought.
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If small or poor-quality eggs are deposited into their pouches,
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some males will absorb them.
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Such males appear to be choosy
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about how they invest their time and energy.
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And some females, in entrusting their eggs to males,
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are being cheated.
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But the male seahorse can't be duped,
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as having a pouch means that he can always be certain
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that all the baby seahorses he gives birth to are his own.
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So male and female seahorses
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have swapped their roles.
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The male is the mother and he gives birth to the babies.
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Another animal with unusual parenting habits is the hyena.
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Here, it's the female that looks and behaves more like a male.
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Why have female hyenas becomes so masculine?
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These are African spotted hyenas,
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creatures that have an undeservedly bad reputation
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and a very strange biology.
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In the wild, they live in clans of up to 80 individuals
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and the females dominate the males.
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The females are big, aggressive,
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and look physically almost exactly like males.
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Unravelling why the female is like this has not been easy,
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as it's difficult to tell the difference between the sexes.
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The female's male appearance
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is made all the more convincing by her reproductive organs -
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they're external and very similar to a male's.
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HYENAS SQUEAK
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Understanding hyena biology
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has helped to explain the female's masculinity
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and the species' reputation as aggressive scavengers.
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But in the past, these strange traits
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gave hyenas a very bad image.
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In the first century, Pliny the Elder described the hyenas
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and did them a great disservice.
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This is what he wrote.
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"Hyenas are like a cross between a dog and a wolf.
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"They break everything with their teeth,
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"swallow it as a gulp
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"and masticate it in the belly.
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"They are believed to become male and female in alternate years.
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"They can imitate the human voice,
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"calling a shepherd by name
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"so that he comes outside, where they tear him to pieces.
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"Any animal that a hyena looks at three times
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"will be unable to move."
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That tainted image of hyenas
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was perpetuated for many years to come,
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and they were branded as evil, dangerous creatures.
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Hyenas are not, of course, evil,
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but their competitive nature and unusual eating habits
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make them appear fearsome.
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They're specialist feeders.
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They crush, eat and digest bones
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that other creatures can't tackle
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and so leave behind.
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And this diet has a significant effect
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on the female's appearance and her family relationships,
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especially those with her cubs.
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In the early 19th century,
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an unusual discovery in Britain
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excited one man to look more closely at the hyena's diet.
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In 1822, a rather eccentric but very eminent geologist
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called William Buckland
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made a significant discovery
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that was to further the modern understanding of hyenas.
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Quarry workers in Kirkdale, Yorkshire,
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had come across a cave that contained a large number of bones.
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Buckland was very excited
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and rushed to see the remains before they were disturbed any further.
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And he found that mud deposits in the cave
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had preserved the bones of over 22 different species of animals,
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including tiger, bear, wolf, elephant
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00:15:24,840 --> 00:15:28,040
and, significantly, hyenas,
263
00:15:28,040 --> 00:15:31,040
which Buckland described as "littering the cave
264
00:15:31,040 --> 00:15:32,960
"like the bones in a dog kennel".
265
00:15:34,280 --> 00:15:39,040
This is one of the actual hyena jaws that Buckland found.
266
00:15:39,040 --> 00:15:42,320
It belonged to a young but ancient hyena.
267
00:15:42,320 --> 00:15:46,520
There were also a lot of these on the cave floor.
268
00:15:46,520 --> 00:15:48,800
They are coprolites,
269
00:15:48,800 --> 00:15:52,480
or fossilised faeces from hyenas.
270
00:15:52,480 --> 00:15:53,840
They contain bone fragments
271
00:15:53,840 --> 00:15:56,760
that have passed through the hyena's digestive tract
272
00:15:56,760 --> 00:16:01,040
and so showed that they were successful bone-crushers.
273
00:16:03,400 --> 00:16:05,960
Buckland's discovery of so many bones
274
00:16:05,960 --> 00:16:08,560
in what he believed to be a hyena's den
275
00:16:08,560 --> 00:16:12,080
indicated that they were very successful hunters.
276
00:16:12,080 --> 00:16:13,960
Contrary to popular belief,
277
00:16:13,960 --> 00:16:15,640
they scavenge very little
278
00:16:15,640 --> 00:16:18,680
and kill over 80% of their own food.
279
00:16:21,600 --> 00:16:25,440
A lone hyena can easily kill a wildebeest or a topi,
280
00:16:25,440 --> 00:16:29,080
and with teamwork they will tackle bigger animals,
281
00:16:29,080 --> 00:16:31,560
like zebra and giraffe.
282
00:16:31,560 --> 00:16:33,600
They do scavenge as well,
283
00:16:33,600 --> 00:16:36,800
but it's more usual for lions to steal from hyenas
284
00:16:36,800 --> 00:16:39,040
rather than the other way around.
285
00:16:40,240 --> 00:16:43,400
Female hyenas have become big and strong
286
00:16:43,400 --> 00:16:46,920
and compete for food with other members of their clan.
287
00:16:46,920 --> 00:16:48,280
Nothing goes to waste -
288
00:16:48,280 --> 00:16:50,640
they can eat even the thickest of bones.
289
00:16:51,960 --> 00:16:56,280
Buckland was fascinated by the marks on the bones from the cave,
290
00:16:56,280 --> 00:16:59,320
but found it hard to believe that hyenas had made them.
291
00:16:59,320 --> 00:17:01,680
He wanted to be sure of his findings
292
00:17:01,680 --> 00:17:03,840
and understand how their jaws,
293
00:17:03,840 --> 00:17:06,960
with their strange, massive teeth, actually worked.
294
00:17:08,480 --> 00:17:11,640
Hyenas are African or Asiatic animals,
295
00:17:11,640 --> 00:17:16,520
so Buckland's discovery of hyena bones in an English cave
296
00:17:16,520 --> 00:17:18,640
was strange, to put it mildly.
297
00:17:18,640 --> 00:17:21,120
As a man of science, he wanted to confirm
298
00:17:21,120 --> 00:17:25,720
that the skull he had collected from Kirkdale was definitely from a hyena
299
00:17:25,720 --> 00:17:29,440
and that it had made the marks on the many fractured bones.
300
00:17:30,480 --> 00:17:32,320
To try and prove his case,
301
00:17:32,320 --> 00:17:35,960
he asked a friend, William Burchill, an African traveller,
302
00:17:35,960 --> 00:17:39,840
to send a young hyena back to England from the Cape.
303
00:17:39,840 --> 00:17:41,040
He planned to kill it
304
00:17:41,040 --> 00:17:44,720
and compare its skull and teeth with the specimens in the cave.
305
00:17:44,720 --> 00:17:48,760
The young hyena that arrived at the docks was already tame
306
00:17:48,760 --> 00:17:51,560
and had become a great favourite with the sailors,
307
00:17:51,560 --> 00:17:53,200
who christened him "Billy".
308
00:17:53,200 --> 00:17:56,400
Billy became quite a celebrity
309
00:17:56,400 --> 00:17:59,160
and was as tame as a pet dog.
310
00:17:59,160 --> 00:18:01,760
No-one could bring themselves to sacrifice him
311
00:18:01,760 --> 00:18:03,440
for the sake of science.
312
00:18:03,440 --> 00:18:07,960
Instead, a search of British museums produced a hyena skull
313
00:18:07,960 --> 00:18:10,000
and Billy's life was spared.
314
00:18:11,200 --> 00:18:14,680
Buckland was then able to compare the new and old skulls,
315
00:18:14,680 --> 00:18:16,440
and they matched.
316
00:18:16,440 --> 00:18:20,040
Billy also helped to clarify the fractures on the bones.
317
00:18:20,040 --> 00:18:24,080
He was fed ox bones, this was one.
318
00:18:24,080 --> 00:18:28,840
And Buckland compared it with one that was found in the cave,
319
00:18:28,840 --> 00:18:30,600
and they closely match.
320
00:18:31,680 --> 00:18:34,400
This ability to crack massive bones
321
00:18:34,400 --> 00:18:38,640
explains why female hyenas look like males.
322
00:18:38,640 --> 00:18:40,520
It's also tied up intricately
323
00:18:40,520 --> 00:18:43,560
with the relationship they have with their cubs.
324
00:18:44,680 --> 00:18:46,360
Cubs are born underground
325
00:18:46,360 --> 00:18:48,920
and are fed on their mother's rich milk.
326
00:18:51,360 --> 00:18:53,000
At about three months of age,
327
00:18:53,000 --> 00:18:54,440
they emerge from the den
328
00:18:54,440 --> 00:18:58,320
and continue to suckle for almost another two years.
329
00:18:58,320 --> 00:19:00,600
Their mother helps feed the youngsters,
330
00:19:00,600 --> 00:19:04,040
as they can't yet crack and crush bones for themselves.
331
00:19:04,040 --> 00:19:06,120
Even at almost a year in age,
332
00:19:06,120 --> 00:19:09,400
when they're big enough to join the kill,
333
00:19:09,400 --> 00:19:12,640
their teeth and jaws are still not sufficiently developed
334
00:19:12,640 --> 00:19:13,840
to tackle big bones.
335
00:19:15,120 --> 00:19:16,560
The skull of a young hyena
336
00:19:16,560 --> 00:19:19,320
is quite different from that of an adult.
337
00:19:19,320 --> 00:19:22,320
It's got a flat top, narrow cheeks
338
00:19:22,320 --> 00:19:25,360
and relatively small teeth.
339
00:19:25,360 --> 00:19:27,200
An animal with a skull like this
340
00:19:27,200 --> 00:19:30,680
would not be able to crush and eat big bones.
341
00:19:30,680 --> 00:19:32,400
It takes almost three years
342
00:19:32,400 --> 00:19:35,000
for a young hyena's skull to grow to full size
343
00:19:35,000 --> 00:19:37,120
and reach mechanical maturity.
344
00:19:37,120 --> 00:19:39,160
And this is the result.
345
00:19:39,160 --> 00:19:42,520
This skull has a large, vaulted forehead
346
00:19:42,520 --> 00:19:44,160
that dissipates biting stress,
347
00:19:44,160 --> 00:19:45,800
carrying it away from the face.
348
00:19:45,800 --> 00:19:48,720
It's also got wide arches at its sides
349
00:19:48,720 --> 00:19:51,160
for the attachment of powerful jaw muscles,
350
00:19:51,160 --> 00:19:54,000
and robust premolars
351
00:19:54,000 --> 00:19:56,520
that have specialised crack-resistant enamel.
352
00:19:56,520 --> 00:19:57,800
Jaws like these
353
00:19:57,800 --> 00:20:01,960
can crack the dense bones of zebra and even giraffe.
354
00:20:04,520 --> 00:20:08,400
Developing this substantial specialised eating equipment
355
00:20:08,400 --> 00:20:09,880
takes time.
356
00:20:09,880 --> 00:20:11,560
So it may be several years
357
00:20:11,560 --> 00:20:14,640
before a young hyena can feed independently.
358
00:20:14,640 --> 00:20:16,840
This puts pressure on their mothers
359
00:20:16,840 --> 00:20:19,800
to become dominant and aggressive.
360
00:20:19,800 --> 00:20:24,400
They need to fight to get enough food for their cubs.
361
00:20:24,400 --> 00:20:27,160
The female's status in the clan's hierarchy
362
00:20:27,160 --> 00:20:29,960
will directly affect the survival of her young.
363
00:20:29,960 --> 00:20:33,160
The biggest, oldest, most established females
364
00:20:33,160 --> 00:20:36,920
are the most dominant and take a bigger share of the kill.
365
00:20:36,920 --> 00:20:39,200
So food and the need to fight for it
366
00:20:39,200 --> 00:20:43,280
has made females look and behave like aggressive males.
367
00:20:43,280 --> 00:20:46,760
But it has also had a strange side effect.
368
00:20:46,760 --> 00:20:52,120
Female hyenas have large amounts of the male hormone testosterone
369
00:20:52,120 --> 00:20:56,120
and, consequently, develop male-like reproductive organs.
370
00:20:56,120 --> 00:20:58,000
This can be a problem.
371
00:20:58,000 --> 00:21:00,000
Having a long, thin birth canal
372
00:21:00,000 --> 00:21:01,960
makes mating very difficult,
373
00:21:01,960 --> 00:21:05,920
and both mothers and cubs sometimes die during birth.
374
00:21:07,200 --> 00:21:09,560
The female's strange gender swap
375
00:21:09,560 --> 00:21:12,360
is one of the most unusual in the animal kingdom.
376
00:21:12,360 --> 00:21:16,160
And new science has now made sense of the old clues
377
00:21:16,160 --> 00:21:18,040
and solved this mystery.
378
00:21:19,120 --> 00:21:21,920
Hyenas are very intriguing animals.
379
00:21:21,920 --> 00:21:25,400
William Buckland's early observations of their bones
380
00:21:25,400 --> 00:21:26,960
in his hyena experiments
381
00:21:26,960 --> 00:21:29,280
started a study of these creatures
382
00:21:29,280 --> 00:21:32,440
that was to reveal their fascinating biology.
383
00:21:32,440 --> 00:21:36,400
Hyenas may have a frightening reputation,
384
00:21:36,400 --> 00:21:39,640
but their odd characteristics all have a reason.
385
00:21:39,640 --> 00:21:42,840
The story of their aggression and bizarre bodies
386
00:21:42,840 --> 00:21:47,360
is intimately tied up with their food and the survival of their cubs.
387
00:21:47,360 --> 00:21:50,760
They've evolved a perfectly formed bone-breaking jaw,
388
00:21:50,760 --> 00:21:52,520
but the time it takes to grow
389
00:21:52,520 --> 00:21:56,240
has resulted in one of the most unusual but dedicated mothers
390
00:21:56,240 --> 00:21:58,200
in the animal kingdom.
391
00:21:58,200 --> 00:22:00,760
So, to become the best parents,
392
00:22:00,760 --> 00:22:03,600
female hyenas have become more male,
393
00:22:03,600 --> 00:22:06,480
and male seahorses more motherly.
394
00:22:12,840 --> 00:22:15,520
Birds build a variety of nests,
395
00:22:15,520 --> 00:22:20,000
each with a design that is characteristic of their species.
396
00:22:20,000 --> 00:22:23,960
The simplest nests are just sticks wedged into position,
397
00:22:23,960 --> 00:22:26,840
but some are more complicated.
398
00:22:26,840 --> 00:22:29,920
The long-tailed tit builds a delicate nest
399
00:22:29,920 --> 00:22:32,920
from plant material and spider silk.
400
00:22:32,920 --> 00:22:37,000
And weaverbirds do, literally, weave with leaves.
401
00:22:40,320 --> 00:22:44,560
But are such skills learned or instinctive?
402
00:22:47,320 --> 00:22:50,640
In 1905, Eugene Marais,
403
00:22:50,640 --> 00:22:53,000
a South African writer and scientist,
404
00:22:53,000 --> 00:22:56,520
was intrigued by the complexity of weaverbird nests.
405
00:22:56,520 --> 00:23:00,520
He wanted to understand more about their nest building skills
406
00:23:00,520 --> 00:23:03,440
and performed a rigorous, but simple, experiment
407
00:23:03,440 --> 00:23:05,640
to see if they learnt how to make nests
408
00:23:05,640 --> 00:23:10,120
or if they built them using what he called "cultural instinct".
409
00:23:10,120 --> 00:23:14,120
He took eggs from a pair of wild weaverbirds
410
00:23:14,120 --> 00:23:18,080
and put them into a canary's nest to hatch.
411
00:23:18,080 --> 00:23:23,080
Then he encouraged the next three generations of weaverbirds to breed,
412
00:23:23,080 --> 00:23:25,240
but gave them no nest material
413
00:23:25,240 --> 00:23:28,880
and hatched their eggs, once again, under canaries.
414
00:23:28,880 --> 00:23:32,760
When nesting time came for the fourth generation of weaverbirds,
415
00:23:32,760 --> 00:23:34,880
he gave them natural nest materials
416
00:23:34,880 --> 00:23:36,440
and, without hesitation,
417
00:23:36,440 --> 00:23:40,200
they vigorously set about constructing perfect wild nests.
418
00:23:42,920 --> 00:23:47,760
So nest-building is largely under genetic control,
419
00:23:47,760 --> 00:23:52,200
but it is influenced by experience and the environment.
420
00:23:52,200 --> 00:23:56,880
Nests of the same kind of weaverbird are not always exactly the same,
421
00:23:56,880 --> 00:24:01,280
and the birds of necessity must have some flexibility in how they build.
422
00:24:03,400 --> 00:24:06,720
Nests that hang are particularly difficult to make,
423
00:24:06,720 --> 00:24:11,360
as the birds have to work against gravity with no support from below.
424
00:24:11,360 --> 00:24:14,000
Weaverbirds solve part of this problem
425
00:24:14,000 --> 00:24:16,080
with a skill none others have.
426
00:24:16,080 --> 00:24:19,280
They're the only birds that can tie knots.
427
00:24:20,720 --> 00:24:23,840
These knots vary and are worked on until the weaver succeeds
428
00:24:23,840 --> 00:24:28,440
in attaching several strands of grass to a suitable branch or stem.
429
00:24:31,280 --> 00:24:33,920
These first fastenings are crucial,
430
00:24:33,920 --> 00:24:37,000
as the whole of the completed nest will hang from them.
431
00:24:42,080 --> 00:24:45,040
Once the birds have secured the foundation,
432
00:24:45,040 --> 00:24:46,680
they can start to weave.
433
00:24:52,600 --> 00:24:57,880
Weaving is just one way of binding leaves together.
434
00:24:57,880 --> 00:24:59,960
There are others.
435
00:25:03,080 --> 00:25:05,560
These are tailorbird nests.
436
00:25:05,560 --> 00:25:09,840
They consist of folded leaves stuffed with soft material
437
00:25:09,840 --> 00:25:12,800
and stitched together using spider's silk.
438
00:25:12,800 --> 00:25:15,640
The tailorbird pierces the leaves with its sharp beak
439
00:25:15,640 --> 00:25:19,960
and then binds them together by pulling silk through the holes.
440
00:25:19,960 --> 00:25:24,200
The complete operation involves a number of different skills.
441
00:25:25,600 --> 00:25:28,520
Making the holes is like riveting.
442
00:25:28,520 --> 00:25:30,600
Two leaves are placed together
443
00:25:30,600 --> 00:25:34,120
and then pierced to create matching holes above and below.
444
00:25:36,800 --> 00:25:39,920
Then the edges are sewn up.
445
00:25:41,320 --> 00:25:45,200
The upper surface of the leaf is kept to the outside
446
00:25:45,200 --> 00:25:47,800
to help the nest look unobtrusive.
447
00:25:50,680 --> 00:25:55,880
The result is a secure pocket, which is then stuffed with a soft lining.
448
00:26:02,040 --> 00:26:07,120
The materials the birds choose to sew up their nest can vary.
449
00:26:07,120 --> 00:26:08,720
At the turn of the century,
450
00:26:08,720 --> 00:26:11,640
there was a report in The Common Birds Of Bombay
451
00:26:11,640 --> 00:26:14,880
of weaverbirds watching carpet makers and tailors
452
00:26:14,880 --> 00:26:16,680
as they worked on verandas.
453
00:26:16,680 --> 00:26:18,400
When the coast was clear,
454
00:26:18,400 --> 00:26:21,720
the birds flew down and stole tiny pieces of thread
455
00:26:21,720 --> 00:26:23,920
with which to sew up their nests.
456
00:26:26,200 --> 00:26:28,280
Birds search with a clear idea
457
00:26:28,280 --> 00:26:31,040
of what will be suitable nest material.
458
00:26:31,040 --> 00:26:33,960
Many use sticks and twigs.
459
00:26:37,600 --> 00:26:40,960
They will, however, occasionally use other material
460
00:26:40,960 --> 00:26:42,440
that does the same job.
461
00:26:43,520 --> 00:26:46,280
And their choices are sometimes surprising.
462
00:26:47,920 --> 00:26:52,560
This nest was found in an aircraft hangar in the 1950s
463
00:26:52,560 --> 00:26:56,080
and it's made entirely of twisted wire.
464
00:26:57,240 --> 00:27:01,160
When it was discovered, it contained two blackbird eggs.
465
00:27:01,160 --> 00:27:03,680
It's an unusual nest for a blackbird,
466
00:27:03,680 --> 00:27:07,480
but similar nests have been found belonging to crows and pigeons.
467
00:27:11,400 --> 00:27:14,320
Weaverbirds work with natural material
468
00:27:14,320 --> 00:27:16,280
and, like the tailorbird,
469
00:27:16,280 --> 00:27:20,320
they have to solve the problem of joining leaves together.
470
00:27:20,320 --> 00:27:23,680
After making a knot to secure the basic framework,
471
00:27:23,680 --> 00:27:25,520
they begin their weaving.
472
00:27:27,000 --> 00:27:29,520
They construct the main egg chamber
473
00:27:29,520 --> 00:27:31,640
and then add a small entrance
474
00:27:31,640 --> 00:27:35,240
around the first securely knotted ring of leaves.
475
00:27:37,960 --> 00:27:42,040
The male, as he works, is under intense scrutiny.
476
00:27:43,720 --> 00:27:45,880
Females are looking for mates,
477
00:27:45,880 --> 00:27:49,280
and males that build firm, well-positioned nests
478
00:27:49,280 --> 00:27:51,040
are favoured as fathers.
479
00:27:52,200 --> 00:27:57,080
When he finishes, a male advertises his handiwork by fluttering.
480
00:27:58,080 --> 00:28:01,400
But he may be forced to build several nests
481
00:28:01,400 --> 00:28:05,360
before a female finally chooses him as a partner.
482
00:28:07,560 --> 00:28:10,600
Weaverbirds' nests are very conspicuous.
483
00:28:11,680 --> 00:28:15,800
Other birds, however, go to some trouble to conceal them.
484
00:28:18,920 --> 00:28:22,720
We may not have tailorbirds or weaverbirds in Britain,
485
00:28:22,720 --> 00:28:25,360
but we do have long-tailed tits.
486
00:28:25,360 --> 00:28:26,680
Delicate little birds
487
00:28:26,680 --> 00:28:30,000
that make intricate and finely constructed nests.
488
00:28:33,000 --> 00:28:35,360
With tiny, repetitive movements,
489
00:28:35,360 --> 00:28:37,600
they use loops of spider's silk
490
00:28:37,600 --> 00:28:40,960
to fell together their mixture of wool and moss.
491
00:28:51,000 --> 00:28:54,600
Both male and female work on the construction.
492
00:28:55,760 --> 00:28:57,640
As the nest takes shape,
493
00:28:57,640 --> 00:28:59,680
they decorate the outside
494
00:28:59,680 --> 00:29:03,280
with several thousand tiny flakes of lichen.
495
00:29:13,560 --> 00:29:16,680
The nest is then lined with hundreds of feathers
496
00:29:16,680 --> 00:29:19,840
and provides a delicate but strong structure
497
00:29:19,840 --> 00:29:21,720
to house the growing chicks.
498
00:29:24,600 --> 00:29:28,280
And it's a nest that's particularly hard to find
499
00:29:28,280 --> 00:29:30,440
because of its covering of lichen.
500
00:29:33,320 --> 00:29:36,880
For years, it was believed that this acted as a sort of camouflage
501
00:29:36,880 --> 00:29:39,200
to help hide the nest.
502
00:29:39,200 --> 00:29:42,240
But the recent discovery of long-tailed tit nests
503
00:29:42,240 --> 00:29:45,320
covered with small flakes of paper and polystyrene
504
00:29:45,320 --> 00:29:50,000
have helped explain more clearly the reason for this decoration.
505
00:29:50,000 --> 00:29:53,960
Rather than helping to blend the nest with its background,
506
00:29:53,960 --> 00:29:58,320
these small flakes reflect light from it, making it almost invisible.
507
00:29:58,320 --> 00:30:03,200
And it seems paper and polystyrene do the job just as well as lichen.
508
00:30:06,520 --> 00:30:10,840
The largest and, perhaps, the most long-lasting nest of all
509
00:30:10,840 --> 00:30:13,280
is made by the social weaverbird.
510
00:30:17,200 --> 00:30:20,000
They live in the dry areas of southern Africa
511
00:30:20,000 --> 00:30:21,280
and work together
512
00:30:21,280 --> 00:30:25,000
to build what looks like a great haystack up in a tree.
513
00:30:27,960 --> 00:30:30,800
New nest chambers are continually added,
514
00:30:30,800 --> 00:30:33,960
as many as 100 pairs of birds may live together
515
00:30:33,960 --> 00:30:36,480
under the one roof, as you might say.
516
00:30:42,640 --> 00:30:46,040
The chambers provide shade during the day
517
00:30:46,040 --> 00:30:48,640
and keep out the chill at night.
518
00:30:54,880 --> 00:30:58,680
And the whole construction is so robust
519
00:30:58,680 --> 00:31:01,280
that it may provide mass housing
520
00:31:01,280 --> 00:31:03,720
for generation after generation of birds.
521
00:31:14,360 --> 00:31:18,480
Recently, the biggest nest ever recorded was discovered
522
00:31:18,480 --> 00:31:22,520
attached to telegraph poles in the Kalahari Desert.
523
00:31:22,520 --> 00:31:25,280
It's more than seven metres across and three metres high.
524
00:31:26,360 --> 00:31:30,520
So weaverbirds make their nests in many different ways
525
00:31:30,520 --> 00:31:34,760
and it was once thought that they worked entirely by instinct,
526
00:31:34,760 --> 00:31:36,080
but this is not so.
527
00:31:36,920 --> 00:31:41,360
They are amongst the most expert nest-builders in the animal kingdom,
528
00:31:41,360 --> 00:31:43,000
and this array of nests
529
00:31:43,000 --> 00:31:45,960
shows the complex and elaborate designs
530
00:31:45,960 --> 00:31:47,760
that they can produce.
531
00:31:47,760 --> 00:31:49,280
Recent studies suggest
532
00:31:49,280 --> 00:31:52,040
that weaverbirds may be using mental skills
533
00:31:52,040 --> 00:31:56,040
that are not dissimilar to those required to make simple tools.
534
00:31:56,040 --> 00:32:00,920
For weaverbirds, a well-built nest is a ticket to successful breeding.
535
00:32:02,760 --> 00:32:06,040
Who would imagine that such complexity could be produced
536
00:32:06,040 --> 00:32:09,320
using just a foot and a beak.
537
00:32:12,200 --> 00:32:15,240
Weaverbirds make their elaborate nests
538
00:32:15,240 --> 00:32:18,440
from simple materials they find around them.
539
00:32:18,440 --> 00:32:22,480
Another of nature's extraordinary builders are the spiders.
540
00:32:22,480 --> 00:32:24,360
They make their complex webs
541
00:32:24,360 --> 00:32:29,600
from an incredible substance they produce themselves, silk.
542
00:32:32,320 --> 00:32:34,720
Spider silk is unique.
543
00:32:34,720 --> 00:32:36,960
It's very thin, very strong,
544
00:32:36,960 --> 00:32:40,000
and has many exciting potential uses.
545
00:32:40,000 --> 00:32:41,920
Spiders spin it with ease,
546
00:32:41,920 --> 00:32:45,120
but scientists have been trying to copy it for many years.
547
00:32:45,120 --> 00:32:48,480
To do that, we need to understand two of the spider's secrets -
548
00:32:48,480 --> 00:32:51,000
the exact structure and nature of their silk,
549
00:32:51,000 --> 00:32:55,280
and the way they transform it from a fluid into a thread.
550
00:32:57,080 --> 00:33:00,600
Spider silk is a truly remarkable material.
551
00:33:00,600 --> 00:33:02,320
It can withstand impact
552
00:33:02,320 --> 00:33:06,640
and it can be strong, stretchy and sticky all at the same time.
553
00:33:07,680 --> 00:33:11,800
Spiders produce it from special glands inside their bodies
554
00:33:11,800 --> 00:33:15,640
and extrude it from tiny nipples called spinnerets
555
00:33:15,640 --> 00:33:18,160
at the back end of their abdomens.
556
00:33:18,160 --> 00:33:21,680
And what is more, they can produce up to seven different kinds,
557
00:33:21,680 --> 00:33:23,600
each with its own purpose.
558
00:33:25,360 --> 00:33:29,440
For centuries, it was the only silk known to man.
559
00:33:29,440 --> 00:33:32,480
The Ancient Greeks used cobwebs to stop bleeding
560
00:33:32,480 --> 00:33:37,280
and Australian Aborigines used it to catch small fish.
561
00:33:37,280 --> 00:33:38,760
Then, in the Far East,
562
00:33:38,760 --> 00:33:42,600
a different and mysterious new kind of silk started to appear,
563
00:33:42,600 --> 00:33:45,160
and in much larger quantities.
564
00:33:46,320 --> 00:33:48,280
According to Chinese legend,
565
00:33:48,280 --> 00:33:52,080
the first person to weave silk into a fabric
566
00:33:52,080 --> 00:33:55,640
was the Empress Leizu, back in the 27th century BC.
567
00:33:56,800 --> 00:34:00,360
She was having tea in her garden under a mulberry tree,
568
00:34:00,360 --> 00:34:03,760
when a cocoon fell from the branch above
569
00:34:03,760 --> 00:34:05,880
and dropped into her cup
570
00:34:05,880 --> 00:34:07,680
and started to unravel.
571
00:34:07,680 --> 00:34:10,720
Whether that's true or not,
572
00:34:10,720 --> 00:34:13,680
the Empress Leizu is now honoured as the goddess of silk.
573
00:34:13,680 --> 00:34:16,000
And silk-moth farming dates back
574
00:34:16,000 --> 00:34:18,880
to the beginning of Chinese civilisation.
575
00:34:18,880 --> 00:34:23,400
The silk was traded right across the Near East and into the Roman Empire.
576
00:34:23,400 --> 00:34:26,520
The Chinese traders were sworn to secrecy
577
00:34:26,520 --> 00:34:29,920
about how this marvellous material was made.
578
00:34:29,920 --> 00:34:32,680
But in the year 532,
579
00:34:32,680 --> 00:34:35,920
the Roman emperor Justinian managed to find out
580
00:34:35,920 --> 00:34:40,400
that it came not, as some suspected, from a spider's web,
581
00:34:40,400 --> 00:34:42,760
but from the cocoon of a moth.
582
00:34:45,000 --> 00:34:48,800
Silk moth caterpillars produce large quantities of silk
583
00:34:48,800 --> 00:34:52,280
and they make it in a very different way to spiders.
584
00:34:52,280 --> 00:34:55,400
The caterpillars feed voraciously on mulberry leaves,
585
00:34:55,400 --> 00:34:59,400
and then, when they're full-grown and ready to transform into a moth,
586
00:34:59,400 --> 00:35:03,240
they spin silken cocoons in which they will pupate.
587
00:35:03,240 --> 00:35:06,920
Unlike spiders, which have specialised spinning organs,
588
00:35:06,920 --> 00:35:10,760
silk moth caterpillars produce silk from their salivary glands.
589
00:35:12,600 --> 00:35:16,360
Each cocoon is made from a single, unbroken filament,
590
00:35:16,360 --> 00:35:20,120
that can be over 500 metres long.
591
00:35:20,120 --> 00:35:24,240
This silk is plentiful and easy to spin commercially,
592
00:35:24,240 --> 00:35:27,560
but it isn't as tough as spider silk.
593
00:35:30,360 --> 00:35:35,400
And spider silk also has more exciting potential uses.
594
00:35:38,560 --> 00:35:39,960
An orb web like this
595
00:35:39,960 --> 00:35:44,280
is constructed over a Y-shaped scaffold of silk threads,
596
00:35:44,280 --> 00:35:46,400
which are extremely strong.
597
00:35:46,400 --> 00:35:51,000
Unlike silkworms, the female spiders, which spin the webs,
598
00:35:51,000 --> 00:35:53,760
are very territorial and aggressive.
599
00:35:53,760 --> 00:35:57,560
So farming and collecting spider silk is very difficult,
600
00:35:57,560 --> 00:35:59,720
but it has been done.
601
00:36:01,600 --> 00:36:05,480
In 1762, a Spanish missionary called Termeyer
602
00:36:05,480 --> 00:36:08,240
made a machine that held a single spider,
603
00:36:08,240 --> 00:36:10,760
from which he pulled a silken thread.
604
00:36:12,200 --> 00:36:15,040
In London, Daniel Rolt, a factory worker,
605
00:36:15,040 --> 00:36:18,680
attached spiders to a small steam machine
606
00:36:18,680 --> 00:36:22,720
and succeeded in reeling out 18 metres of silk a minute.
607
00:36:22,720 --> 00:36:27,760
That led to machines that were able to milk several spiders at a time.
608
00:36:31,280 --> 00:36:34,480
Experiments then stopped, until 2004,
609
00:36:34,480 --> 00:36:37,320
when two textile artists in Madagascar
610
00:36:37,320 --> 00:36:40,600
built a machine based on these early designs,
611
00:36:40,600 --> 00:36:43,920
with which they made something very special indeed.
612
00:36:45,480 --> 00:36:49,680
The golden colour of this stunningly beautiful spider silk shawl
613
00:36:49,680 --> 00:36:51,920
is completely natural.
614
00:36:51,920 --> 00:36:54,360
The silk from which it was made
615
00:36:54,360 --> 00:36:58,280
was produced by 1,063,000 spiders,
616
00:36:58,280 --> 00:37:01,880
like this one, over four years.
617
00:37:01,880 --> 00:37:05,440
Local people collected 3,000 spiders a day
618
00:37:05,440 --> 00:37:08,440
and trained handlers extracted silk
619
00:37:08,440 --> 00:37:10,640
from groups of 24 at a time.
620
00:37:10,640 --> 00:37:15,400
After being milked, the spiders were released back into the wild.
621
00:37:15,400 --> 00:37:19,080
The individual silk strands were then twisted into a thread
622
00:37:19,080 --> 00:37:23,840
which was woven into this intricately patterned fabric on looms.
623
00:37:27,400 --> 00:37:29,800
Now, this kind of silk fabric production
624
00:37:29,800 --> 00:37:31,640
couldn't work commercially.
625
00:37:31,640 --> 00:37:34,520
Apart from being hard work to make in quantity,
626
00:37:34,520 --> 00:37:39,280
spider silk isn't really a very suitable thread for fabric.
627
00:37:39,280 --> 00:37:42,920
As a cloth it reacts badly to moisture and heat,
628
00:37:42,920 --> 00:37:46,080
but in its natural state, as a single thread,
629
00:37:46,080 --> 00:37:48,280
it has physical qualities
630
00:37:48,280 --> 00:37:50,680
that could be exploited medically.
631
00:37:50,680 --> 00:37:53,240
These special characteristics
632
00:37:53,240 --> 00:37:58,360
are a consequence of the molecular structure of spider silk.
633
00:37:58,360 --> 00:38:02,280
It consists of two large protein molecules.
634
00:38:02,280 --> 00:38:04,560
One is stretchy and spaghetti-like,
635
00:38:04,560 --> 00:38:07,760
and the other has a harder, crystalline structure.
636
00:38:07,760 --> 00:38:09,840
Combined, these two proteins
637
00:38:09,840 --> 00:38:13,920
give silk unique qualities of strength and flexibility.
638
00:38:15,440 --> 00:38:19,320
Spiders store these proteins as a gel-like liquid in their bodies.
639
00:38:19,320 --> 00:38:20,880
And when they need to make silk,
640
00:38:20,880 --> 00:38:23,360
they extrude it through the spinnerets,
641
00:38:23,360 --> 00:38:25,920
combining the molecules in a special way.
642
00:38:27,200 --> 00:38:30,160
If we hold down a spider without harming it
643
00:38:30,160 --> 00:38:32,960
we can see this process in more detail.
644
00:38:32,960 --> 00:38:37,240
Normally, the spider would attach the end of the silk filament
645
00:38:37,240 --> 00:38:39,560
to an object and then move away,
646
00:38:39,560 --> 00:38:42,560
so that the filament is pulled from the spinnerets.
647
00:38:42,560 --> 00:38:45,160
We can produce the same reaction,
648
00:38:45,160 --> 00:38:48,480
by gently pulling the end of the filament itself.
649
00:38:48,480 --> 00:38:51,520
Internally, the silk liquid is passing down a long duct
650
00:38:51,520 --> 00:38:56,120
in which stretchy elements within the protein molecules
651
00:38:56,120 --> 00:38:58,400
are lined with harder crystalline ones,
652
00:38:58,400 --> 00:39:01,720
to create an extremely strong and tough thread.
653
00:39:04,840 --> 00:39:07,160
Scanning electron microscopes
654
00:39:07,160 --> 00:39:10,800
reveal how the liquid emerges from the spinnerets.
655
00:39:10,800 --> 00:39:14,240
Incredibly, spiders can convert liquid proteins
656
00:39:14,240 --> 00:39:17,360
into a hardened thread at room temperature
657
00:39:17,360 --> 00:39:19,200
with very little energy.
658
00:39:19,200 --> 00:39:21,920
If we could understand and copy this process,
659
00:39:21,920 --> 00:39:25,000
it would be a major scientific breakthrough.
660
00:39:26,880 --> 00:39:29,400
Scientists have, in fact, spent many years
661
00:39:29,400 --> 00:39:33,320
trying to replicate the spider's liquid silk and the way it's spun.
662
00:39:33,320 --> 00:39:37,680
Recently, the genes of spider-silk proteins were cloned
663
00:39:37,680 --> 00:39:39,440
and put into goats
664
00:39:39,440 --> 00:39:42,160
to try and produce silk in their milk.
665
00:39:42,160 --> 00:39:45,720
It worked, and when the goats had kids
666
00:39:45,720 --> 00:39:49,120
silk proteins were extracted from the mother's milk.
667
00:39:51,160 --> 00:39:52,880
But none of these processes
668
00:39:52,880 --> 00:39:57,480
have yet produced silk that is as tough as natural spider silk.
669
00:39:59,160 --> 00:40:01,960
This machine is called a tensile tester
670
00:40:01,960 --> 00:40:05,920
and it shows how strong and stretchy spider silk can be.
671
00:40:05,920 --> 00:40:10,600
This dragline silk is being pulled apart,
672
00:40:10,600 --> 00:40:13,120
and a graph shows the force the fibre is taking
673
00:40:13,120 --> 00:40:15,280
and at what point it breaks.
674
00:40:15,280 --> 00:40:17,480
A steel thread of similar diameter
675
00:40:17,480 --> 00:40:19,400
would have broken by now.
676
00:40:25,440 --> 00:40:27,880
There, it's broken.
677
00:40:27,880 --> 00:40:32,640
Spider silk is the toughest natural material known to man.
678
00:40:35,160 --> 00:40:37,840
A single thread of web silk,
679
00:40:37,840 --> 00:40:39,400
less than a millimetre thick,
680
00:40:39,400 --> 00:40:42,520
can absorb the impact of fast-moving prey
681
00:40:42,520 --> 00:40:45,440
and bring it to a halt without breaking.
682
00:40:45,440 --> 00:40:48,760
Complete webs can stretch enormously
683
00:40:48,760 --> 00:40:51,440
and then return to their original shape
684
00:40:51,440 --> 00:40:52,920
with a minimum of damage.
685
00:40:55,920 --> 00:41:00,200
Incredibly, spiders can make this complex material
686
00:41:00,200 --> 00:41:03,240
from just fresh air, flies and water.
687
00:41:04,400 --> 00:41:07,240
The best we can do in making a material like it
688
00:41:07,240 --> 00:41:11,000
requires oil, chemicals and a great deal of energy.
689
00:41:13,760 --> 00:41:16,920
Although we now better understand the structure of spider silk
690
00:41:16,920 --> 00:41:19,160
and the natural spinning process,
691
00:41:19,160 --> 00:41:21,800
we still can't perform the spider's magic
692
00:41:21,800 --> 00:41:24,440
and copy this extraordinary substance.
693
00:41:25,720 --> 00:41:29,480
But using small amounts of natural spider silk in clever ways
694
00:41:29,480 --> 00:41:32,920
has, nonetheless, a very exciting future.
695
00:41:34,040 --> 00:41:36,320
A sumptuous golden cloth
696
00:41:36,320 --> 00:41:39,080
is just one possible product.
697
00:41:40,520 --> 00:41:44,600
This is a dream that has become a reality,
698
00:41:44,600 --> 00:41:47,560
and shows just how lovely spider silk can be.
699
00:41:48,920 --> 00:41:51,120
But it also has the potential
700
00:41:51,120 --> 00:41:53,080
to make other dreams come true.
701
00:41:53,080 --> 00:41:56,360
It's a biodegradable material
702
00:41:56,360 --> 00:41:59,640
that we're now using to make artificial joints,
703
00:41:59,640 --> 00:42:03,560
and it may even help repair damaged spinal tissue.
704
00:42:04,960 --> 00:42:10,240
This curiosity of nature could, eventually, save lives.
57706
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