0:00:02 > 0:00:06The natural world is full of extraordinary animals
0:00:06 > 0:00:08with amazing life histories.
0:00:09 > 0:00:13Yet certain stories are more intriguing than most.
0:00:15 > 0:00:19The mysteries of a butterfly's life cycle,
0:00:19 > 0:00:22or the strange biology of the emperor penguin.
0:00:23 > 0:00:25Some of these creatures
0:00:25 > 0:00:28were surrounded by myth and misunderstandings
0:00:28 > 0:00:29for a very long time.
0:00:30 > 0:00:33And some have only recently revealed their secrets.
0:00:35 > 0:00:38These are the animals that stand out from the crowd.
0:00:38 > 0:00:43The curiosities I find most fascinating of all.
0:00:51 > 0:00:55Animals are usually either male or female.
0:00:55 > 0:00:58And, usually, they behave in a way
0:00:58 > 0:01:00that is characteristic of their gender.
0:01:00 > 0:01:04But in nature, there are always curious exceptions.
0:01:05 > 0:01:09Female hyenas behave and look like males.
0:01:11 > 0:01:13And male seahorses play mother
0:01:13 > 0:01:15and physically give birth.
0:01:16 > 0:01:19Only now are we beginning to understand
0:01:19 > 0:01:24why these two animals seem to have swapped their sexual identities.
0:01:27 > 0:01:29And also in this programme,
0:01:29 > 0:01:33spiders spin intricate webs using their own silk.
0:01:33 > 0:01:37And birds weave nests from strips of leaves.
0:01:37 > 0:01:41I investigate the skill of these spinners and weavers
0:01:41 > 0:01:43and the way they use such materials
0:01:43 > 0:01:46to produce such truly complex structures.
0:01:54 > 0:01:57Seahorses are fascinating.
0:01:57 > 0:02:01Some are tiny and blend perfectly with their surroundings.
0:02:01 > 0:02:06Others could grow to an impressive 35 centimetres in size.
0:02:06 > 0:02:10They live in shallow waters, both tropical and temperate,
0:02:10 > 0:02:11across much of the world,
0:02:11 > 0:02:15and have even been found in the Thames Estuary near London.
0:02:15 > 0:02:18Seeing one for the first time is a moment to remember.
0:02:20 > 0:02:24They're magical creatures, with a truly fantastic appearance.
0:02:24 > 0:02:27They have the head of a horse, eyes like a chameleon,
0:02:27 > 0:02:30the prehensile tail of a monkey,
0:02:30 > 0:02:32armour that can change colour
0:02:32 > 0:02:35and, perhaps most strangely of all, a pouch.
0:02:35 > 0:02:39Their unusual features inspired their name, Hippocampus,
0:02:39 > 0:02:41a combination of two Greek words -
0:02:41 > 0:02:46hippo, meaning "horse", and kampos, meaning "sea monster".
0:02:46 > 0:02:48For centuries, they've been considered
0:02:48 > 0:02:50animals of myth and legend,
0:02:50 > 0:02:53and only today are we unravelling the true story
0:02:53 > 0:02:56of males that give birth.
0:02:58 > 0:03:02Seahorses baffled early naturalists.
0:03:02 > 0:03:06Their unusual characteristics seemed to make them misfits.
0:03:06 > 0:03:07But after much debate,
0:03:07 > 0:03:10they were recognised as true bony fish.
0:03:11 > 0:03:15But their breeding habits were hardly fishy.
0:03:15 > 0:03:21Typically, female fish release large numbers of eggs into the sea
0:03:21 > 0:03:23that males must quickly fertilise.
0:03:23 > 0:03:28But a fish that kept its eggs in a pouch seemed scarcely believable.
0:03:29 > 0:03:31The seahorse's striking appearance
0:03:31 > 0:03:34has given it an almost magical status.
0:03:34 > 0:03:37Images and stories of a creature, part horse, part fish,
0:03:37 > 0:03:41have spanned the centuries across many cultures.
0:03:41 > 0:03:45Among the most famous are those belonging to Poseidon.
0:03:45 > 0:03:48This famous Greek god of the sea
0:03:48 > 0:03:49lived below the waves,
0:03:49 > 0:03:54and his golden chariot was pulled by a pair of giant hippocampi.
0:03:55 > 0:03:58The seahorse's odd behaviour appeared mysterious, too.
0:03:58 > 0:04:00As early as the third century BC,
0:04:00 > 0:04:04Aristotle noted in his book on the history of animals
0:04:04 > 0:04:07that pipefish, close relatives of the seahorse,
0:04:07 > 0:04:10had a pouch that burst into two
0:04:10 > 0:04:12to release the young.
0:04:13 > 0:04:15These early observations
0:04:15 > 0:04:17of the pipefish's strange breeding behaviour
0:04:17 > 0:04:19help to reveal the true story
0:04:19 > 0:04:22of the male seahorse's mysterious pouch.
0:04:24 > 0:04:27Just like seahorses, pipefish carry their eggs around with them.
0:04:28 > 0:04:33Some species simply stick the eggs to the outside of their bodies.
0:04:33 > 0:04:36Others have a rudimentary pouch.
0:04:38 > 0:04:41These simpler techniques provide some clues
0:04:41 > 0:04:46as to how seahorses developed their more complex closed pouch.
0:04:49 > 0:04:51But what Aristotle didn't know
0:04:51 > 0:04:54when he spotted the pipefish giving birth,
0:04:54 > 0:04:56was that he was actually looking at a male.
0:04:56 > 0:04:58And this important detail
0:04:58 > 0:05:02was to remain undiscovered for hundreds of years.
0:05:06 > 0:05:09Although seahorses live in British waters,
0:05:09 > 0:05:12until Victorian times few people apart from fishermen
0:05:12 > 0:05:14had ever seen them.
0:05:14 > 0:05:19In 1859, a Mr Pinto brought four live seahorses back to London
0:05:19 > 0:05:22from the mouth of the River Tagus in Portugal.
0:05:22 > 0:05:27Pinto endured a sleepless seven-day train journey through Europe,
0:05:27 > 0:05:29waking himself frequently
0:05:29 > 0:05:32to aerate the seahorse's water with a syringe.
0:05:33 > 0:05:35His seahorses survived
0:05:35 > 0:05:38and were installed in the new London Aquarium.
0:05:38 > 0:05:40They were an instant hit.
0:05:42 > 0:05:45Seahorses were headline news.
0:05:45 > 0:05:49Mr Pinto's journey and their arrival made the front pages.
0:05:49 > 0:05:52Now they could be seen in great detail,
0:05:52 > 0:05:55and the study of their mysterious breeding began.
0:05:56 > 0:05:57In that same year,
0:05:57 > 0:06:01what was described as a "herd" of baby seahorses
0:06:01 > 0:06:04was born in the British Midlands Aquarium.
0:06:04 > 0:06:08This caused quite a stir, as did the discovery
0:06:08 > 0:06:11that it was the male that gave birth to the young.
0:06:13 > 0:06:17But why seahorses swapped parenting roles remained a mystery,
0:06:17 > 0:06:20and we're still searching for the answers today.
0:06:22 > 0:06:25Here at the London Zoo's aquarium,
0:06:25 > 0:06:28over 150 years since the arrival of the first seahorses,
0:06:28 > 0:06:32a detailed study is revealing more about their reproduction
0:06:32 > 0:06:34and the usual role of the male.
0:06:34 > 0:06:39These tanks are set like a seahorse dating centre,
0:06:39 > 0:06:41the first port of call
0:06:41 > 0:06:45is the courtship aquarium, or ballroom tank.
0:06:45 > 0:06:47Here, a number of adult seahorses
0:06:47 > 0:06:49spend time getting to know each other
0:06:49 > 0:06:51as they look for compatible partners.
0:06:51 > 0:06:56Breeding seahorses form lasting partnerships as mating pairs,
0:06:56 > 0:06:58and their long, elaborate courtship dances
0:06:58 > 0:07:02are a way of finding and securing a suitable mate.
0:07:05 > 0:07:08Dances like those of this Australian species
0:07:08 > 0:07:12can be complex and last several days.
0:07:14 > 0:07:16They help the couple synchronise their bodies
0:07:16 > 0:07:19so that the male's pouch is ready for the eggs.
0:07:22 > 0:07:25They also help to establish the couple's joint territory.
0:07:30 > 0:07:32Seahorses were thought to be monogamous,
0:07:32 > 0:07:36but we now know that some are only exclusive couples
0:07:36 > 0:07:39for the duration of the breeding season.
0:07:39 > 0:07:41The female must choose the right male
0:07:41 > 0:07:44because she's going to pass over her precious eggs to him.
0:07:46 > 0:07:49Female seahorses do not have a pouch,
0:07:49 > 0:07:52so a strong pair-bond with a male is very important,
0:07:52 > 0:07:55as he will care for her eggs.
0:07:55 > 0:07:58This is the honeymoon tank.
0:07:58 > 0:08:01Seahorses that have shown an attraction for each other
0:08:01 > 0:08:02in the courtship tank
0:08:02 > 0:08:04are removed as a couple
0:08:04 > 0:08:06and given their own private space.
0:08:06 > 0:08:10In the wild, each pair has its own territory
0:08:10 > 0:08:13and these smaller tanks make captive breeding more successful.
0:08:13 > 0:08:17Here, the pair can synchronise their courtship.
0:08:17 > 0:08:19Timing is crucial.
0:08:19 > 0:08:21The female's eggs must be fully developed
0:08:21 > 0:08:23at exactly the same time
0:08:23 > 0:08:25that the male's pouch is ready to receive them.
0:08:28 > 0:08:30Once the female's eggs are ready,
0:08:30 > 0:08:33she hydrates them with seawater.
0:08:33 > 0:08:36They must then be laid within 24 hours.
0:08:37 > 0:08:40She transfers her eggs to her partner
0:08:40 > 0:08:44by inserting her egg-laying tube, or ovipositor,
0:08:44 > 0:08:46into the male's pouch.
0:08:49 > 0:08:52Once pregnant, the male attaches himself to one spot
0:08:52 > 0:08:55and the female visits him every day.
0:08:56 > 0:09:00She checks to see when he'll be ready for her next batch of eggs.
0:09:03 > 0:09:07One theory suggests that because the male is incubating the eggs,
0:09:07 > 0:09:09the female has more time to feed
0:09:09 > 0:09:12and can put energy into making new eggs more quickly.
0:09:14 > 0:09:17Swapping roles may be a smart way
0:09:17 > 0:09:20to use their resources more efficiently.
0:09:25 > 0:09:28What goes on inside the pouch is still a mystery.
0:09:30 > 0:09:33The male may simply provide a closed incubator.
0:09:34 > 0:09:37Or the inner skin may develop extra blood vessels
0:09:37 > 0:09:40to give a more placenta-like connection.
0:09:40 > 0:09:41It's not clear.
0:09:42 > 0:09:44During pregnancy and birth
0:09:44 > 0:09:47the male's metabolism increases,
0:09:47 > 0:09:49but that's little wonder,
0:09:49 > 0:09:52for he may have up to 1,500 eggs in his pouch.
0:09:57 > 0:10:01The male seahorse gives birth to dozens of miniature babies,
0:10:01 > 0:10:03perfect in every detail.
0:10:03 > 0:10:07The free-swimming young are put into separate creche tanks
0:10:07 > 0:10:10where they can be fed and cared for.
0:10:10 > 0:10:14The parent seahorses in this biological hotel
0:10:14 > 0:10:16remain in the honeymoon suite
0:10:16 > 0:10:17ready to mate again.
0:10:19 > 0:10:21These are some of last year's youngsters
0:10:21 > 0:10:23and they've grown enormously.
0:10:23 > 0:10:26Next year, they'll be breeding themselves.
0:10:29 > 0:10:32Swapping the parental roles
0:10:32 > 0:10:34seems to work well for seahorses.
0:10:35 > 0:10:41In warm conditions, a male can give birth every 28-30 days.
0:10:41 > 0:10:45But of the thousands of fry produced each year, only a few survive.
0:10:46 > 0:10:49There is no safe creche in the open sea.
0:10:51 > 0:10:55To succeed, seahorse parents must work well together,
0:10:55 > 0:10:57yet in this partnership,
0:10:57 > 0:10:59the female seems to have the freedom
0:10:59 > 0:11:02to swim, feed, and patrol the territory,
0:11:02 > 0:11:05which is normally the prerogative of the male.
0:11:07 > 0:11:13So, is the male seahorse a slave to a gallivanting female?
0:11:13 > 0:11:16Well, latest research suggests not,
0:11:16 > 0:11:19and shows that some males may have more control over breeding
0:11:19 > 0:11:21than first thought.
0:11:21 > 0:11:26If small or poor-quality eggs are deposited into their pouches,
0:11:26 > 0:11:29some males will absorb them.
0:11:29 > 0:11:31Such males appear to be choosy
0:11:31 > 0:11:34about how they invest their time and energy.
0:11:34 > 0:11:38And some females, in entrusting their eggs to males,
0:11:38 > 0:11:40are being cheated.
0:11:40 > 0:11:42But the male seahorse can't be duped,
0:11:42 > 0:11:46as having a pouch means that he can always be certain
0:11:46 > 0:11:49that all the baby seahorses he gives birth to are his own.
0:11:51 > 0:11:54So male and female seahorses
0:11:54 > 0:11:56have swapped their roles.
0:11:56 > 0:12:00The male is the mother and he gives birth to the babies.
0:12:02 > 0:12:06Another animal with unusual parenting habits is the hyena.
0:12:06 > 0:12:10Here, it's the female that looks and behaves more like a male.
0:12:10 > 0:12:15Why have female hyenas becomes so masculine?
0:12:18 > 0:12:21These are African spotted hyenas,
0:12:21 > 0:12:25creatures that have an undeservedly bad reputation
0:12:25 > 0:12:27and a very strange biology.
0:12:27 > 0:12:31In the wild, they live in clans of up to 80 individuals
0:12:31 > 0:12:33and the females dominate the males.
0:12:33 > 0:12:36The females are big, aggressive,
0:12:36 > 0:12:39and look physically almost exactly like males.
0:12:42 > 0:12:45Unravelling why the female is like this has not been easy,
0:12:45 > 0:12:49as it's difficult to tell the difference between the sexes.
0:12:50 > 0:12:52The female's male appearance
0:12:52 > 0:12:56is made all the more convincing by her reproductive organs -
0:12:56 > 0:12:59they're external and very similar to a male's.
0:12:59 > 0:13:02HYENAS SQUEAK
0:13:02 > 0:13:04Understanding hyena biology
0:13:04 > 0:13:07has helped to explain the female's masculinity
0:13:07 > 0:13:11and the species' reputation as aggressive scavengers.
0:13:12 > 0:13:15But in the past, these strange traits
0:13:15 > 0:13:17gave hyenas a very bad image.
0:13:19 > 0:13:23In the first century, Pliny the Elder described the hyenas
0:13:23 > 0:13:25and did them a great disservice.
0:13:25 > 0:13:27This is what he wrote.
0:13:27 > 0:13:32"Hyenas are like a cross between a dog and a wolf.
0:13:32 > 0:13:34"They break everything with their teeth,
0:13:34 > 0:13:36"swallow it as a gulp
0:13:36 > 0:13:39"and masticate it in the belly.
0:13:39 > 0:13:44"They are believed to become male and female in alternate years.
0:13:44 > 0:13:47"They can imitate the human voice,
0:13:47 > 0:13:49"calling a shepherd by name
0:13:49 > 0:13:52"so that he comes outside, where they tear him to pieces.
0:13:52 > 0:13:57"Any animal that a hyena looks at three times
0:13:57 > 0:13:59"will be unable to move."
0:13:59 > 0:14:01That tainted image of hyenas
0:14:01 > 0:14:03was perpetuated for many years to come,
0:14:03 > 0:14:07and they were branded as evil, dangerous creatures.
0:14:09 > 0:14:12Hyenas are not, of course, evil,
0:14:12 > 0:14:15but their competitive nature and unusual eating habits
0:14:15 > 0:14:17make them appear fearsome.
0:14:18 > 0:14:20They're specialist feeders.
0:14:20 > 0:14:22They crush, eat and digest bones
0:14:22 > 0:14:25that other creatures can't tackle
0:14:25 > 0:14:26and so leave behind.
0:14:27 > 0:14:31And this diet has a significant effect
0:14:31 > 0:14:35on the female's appearance and her family relationships,
0:14:35 > 0:14:37especially those with her cubs.
0:14:38 > 0:14:40In the early 19th century,
0:14:40 > 0:14:43an unusual discovery in Britain
0:14:43 > 0:14:47excited one man to look more closely at the hyena's diet.
0:14:48 > 0:14:53In 1822, a rather eccentric but very eminent geologist
0:14:53 > 0:14:54called William Buckland
0:14:54 > 0:14:56made a significant discovery
0:14:56 > 0:15:00that was to further the modern understanding of hyenas.
0:15:01 > 0:15:03Quarry workers in Kirkdale, Yorkshire,
0:15:03 > 0:15:08had come across a cave that contained a large number of bones.
0:15:08 > 0:15:10Buckland was very excited
0:15:10 > 0:15:14and rushed to see the remains before they were disturbed any further.
0:15:14 > 0:15:17And he found that mud deposits in the cave
0:15:17 > 0:15:21had preserved the bones of over 22 different species of animals,
0:15:21 > 0:15:24including tiger, bear, wolf, elephant
0:15:24 > 0:15:28and, significantly, hyenas,
0:15:28 > 0:15:31which Buckland described as "littering the cave
0:15:31 > 0:15:32"like the bones in a dog kennel".
0:15:34 > 0:15:39This is one of the actual hyena jaws that Buckland found.
0:15:39 > 0:15:42It belonged to a young but ancient hyena.
0:15:42 > 0:15:46There were also a lot of these on the cave floor.
0:15:46 > 0:15:48They are coprolites,
0:15:48 > 0:15:52or fossilised faeces from hyenas.
0:15:52 > 0:15:53They contain bone fragments
0:15:53 > 0:15:56that have passed through the hyena's digestive tract
0:15:56 > 0:16:01and so showed that they were successful bone-crushers.
0:16:03 > 0:16:05Buckland's discovery of so many bones
0:16:05 > 0:16:08in what he believed to be a hyena's den
0:16:08 > 0:16:12indicated that they were very successful hunters.
0:16:12 > 0:16:13Contrary to popular belief,
0:16:13 > 0:16:15they scavenge very little
0:16:15 > 0:16:18and kill over 80% of their own food.
0:16:21 > 0:16:25A lone hyena can easily kill a wildebeest or a topi,
0:16:25 > 0:16:29and with teamwork they will tackle bigger animals,
0:16:29 > 0:16:31like zebra and giraffe.
0:16:31 > 0:16:33They do scavenge as well,
0:16:33 > 0:16:36but it's more usual for lions to steal from hyenas
0:16:36 > 0:16:39rather than the other way around.
0:16:40 > 0:16:43Female hyenas have become big and strong
0:16:43 > 0:16:46and compete for food with other members of their clan.
0:16:46 > 0:16:48Nothing goes to waste -
0:16:48 > 0:16:50they can eat even the thickest of bones.
0:16:51 > 0:16:56Buckland was fascinated by the marks on the bones from the cave,
0:16:56 > 0:16:59but found it hard to believe that hyenas had made them.
0:16:59 > 0:17:01He wanted to be sure of his findings
0:17:01 > 0:17:03and understand how their jaws,
0:17:03 > 0:17:06with their strange, massive teeth, actually worked.
0:17:08 > 0:17:11Hyenas are African or Asiatic animals,
0:17:11 > 0:17:16so Buckland's discovery of hyena bones in an English cave
0:17:16 > 0:17:18was strange, to put it mildly.
0:17:18 > 0:17:21As a man of science, he wanted to confirm
0:17:21 > 0:17:25that the skull he had collected from Kirkdale was definitely from a hyena
0:17:25 > 0:17:29and that it had made the marks on the many fractured bones.
0:17:30 > 0:17:32To try and prove his case,
0:17:32 > 0:17:35he asked a friend, William Burchill, an African traveller,
0:17:35 > 0:17:39to send a young hyena back to England from the Cape.
0:17:39 > 0:17:41He planned to kill it
0:17:41 > 0:17:44and compare its skull and teeth with the specimens in the cave.
0:17:44 > 0:17:48The young hyena that arrived at the docks was already tame
0:17:48 > 0:17:51and had become a great favourite with the sailors,
0:17:51 > 0:17:53who christened him "Billy".
0:17:53 > 0:17:56Billy became quite a celebrity
0:17:56 > 0:17:59and was as tame as a pet dog.
0:17:59 > 0:18:01No-one could bring themselves to sacrifice him
0:18:01 > 0:18:03for the sake of science.
0:18:03 > 0:18:07Instead, a search of British museums produced a hyena skull
0:18:07 > 0:18:10and Billy's life was spared.
0:18:11 > 0:18:14Buckland was then able to compare the new and old skulls,
0:18:14 > 0:18:16and they matched.
0:18:16 > 0:18:20Billy also helped to clarify the fractures on the bones.
0:18:20 > 0:18:24He was fed ox bones, this was one.
0:18:24 > 0:18:28And Buckland compared it with one that was found in the cave,
0:18:28 > 0:18:30and they closely match.
0:18:31 > 0:18:34This ability to crack massive bones
0:18:34 > 0:18:38explains why female hyenas look like males.
0:18:38 > 0:18:40It's also tied up intricately
0:18:40 > 0:18:43with the relationship they have with their cubs.
0:18:44 > 0:18:46Cubs are born underground
0:18:46 > 0:18:48and are fed on their mother's rich milk.
0:18:51 > 0:18:53At about three months of age,
0:18:53 > 0:18:54they emerge from the den
0:18:54 > 0:18:58and continue to suckle for almost another two years.
0:18:58 > 0:19:00Their mother helps feed the youngsters,
0:19:00 > 0:19:04as they can't yet crack and crush bones for themselves.
0:19:04 > 0:19:06Even at almost a year in age,
0:19:06 > 0:19:09when they're big enough to join the kill,
0:19:09 > 0:19:12their teeth and jaws are still not sufficiently developed
0:19:12 > 0:19:13to tackle big bones.
0:19:15 > 0:19:16The skull of a young hyena
0:19:16 > 0:19:19is quite different from that of an adult.
0:19:19 > 0:19:22It's got a flat top, narrow cheeks
0:19:22 > 0:19:25and relatively small teeth.
0:19:25 > 0:19:27An animal with a skull like this
0:19:27 > 0:19:30would not be able to crush and eat big bones.
0:19:30 > 0:19:32It takes almost three years
0:19:32 > 0:19:35for a young hyena's skull to grow to full size
0:19:35 > 0:19:37and reach mechanical maturity.
0:19:37 > 0:19:39And this is the result.
0:19:39 > 0:19:42This skull has a large, vaulted forehead
0:19:42 > 0:19:44that dissipates biting stress,
0:19:44 > 0:19:45carrying it away from the face.
0:19:45 > 0:19:48It's also got wide arches at its sides
0:19:48 > 0:19:51for the attachment of powerful jaw muscles,
0:19:51 > 0:19:54and robust premolars
0:19:54 > 0:19:56that have specialised crack-resistant enamel.
0:19:56 > 0:19:57Jaws like these
0:19:57 > 0:20:01can crack the dense bones of zebra and even giraffe.
0:20:04 > 0:20:08Developing this substantial specialised eating equipment
0:20:08 > 0:20:09takes time.
0:20:09 > 0:20:11So it may be several years
0:20:11 > 0:20:14before a young hyena can feed independently.
0:20:14 > 0:20:16This puts pressure on their mothers
0:20:16 > 0:20:19to become dominant and aggressive.
0:20:19 > 0:20:24They need to fight to get enough food for their cubs.
0:20:24 > 0:20:27The female's status in the clan's hierarchy
0:20:27 > 0:20:29will directly affect the survival of her young.
0:20:29 > 0:20:33The biggest, oldest, most established females
0:20:33 > 0:20:36are the most dominant and take a bigger share of the kill.
0:20:36 > 0:20:39So food and the need to fight for it
0:20:39 > 0:20:43has made females look and behave like aggressive males.
0:20:43 > 0:20:46But it has also had a strange side effect.
0:20:46 > 0:20:52Female hyenas have large amounts of the male hormone testosterone
0:20:52 > 0:20:56and, consequently, develop male-like reproductive organs.
0:20:56 > 0:20:58This can be a problem.
0:20:58 > 0:21:00Having a long, thin birth canal
0:21:00 > 0:21:01makes mating very difficult,
0:21:01 > 0:21:05and both mothers and cubs sometimes die during birth.
0:21:07 > 0:21:09The female's strange gender swap
0:21:09 > 0:21:12is one of the most unusual in the animal kingdom.
0:21:12 > 0:21:16And new science has now made sense of the old clues
0:21:16 > 0:21:18and solved this mystery.
0:21:19 > 0:21:21Hyenas are very intriguing animals.
0:21:21 > 0:21:25William Buckland's early observations of their bones
0:21:25 > 0:21:26in his hyena experiments
0:21:26 > 0:21:29started a study of these creatures
0:21:29 > 0:21:32that was to reveal their fascinating biology.
0:21:32 > 0:21:36Hyenas may have a frightening reputation,
0:21:36 > 0:21:39but their odd characteristics all have a reason.
0:21:39 > 0:21:42The story of their aggression and bizarre bodies
0:21:42 > 0:21:47is intimately tied up with their food and the survival of their cubs.
0:21:47 > 0:21:50They've evolved a perfectly formed bone-breaking jaw,
0:21:50 > 0:21:52but the time it takes to grow
0:21:52 > 0:21:56has resulted in one of the most unusual but dedicated mothers
0:21:56 > 0:21:58in the animal kingdom.
0:21:58 > 0:22:00So, to become the best parents,
0:22:00 > 0:22:03female hyenas have become more male,
0:22:03 > 0:22:06and male seahorses more motherly.
0:22:12 > 0:22:15Birds build a variety of nests,
0:22:15 > 0:22:20each with a design that is characteristic of their species.
0:22:20 > 0:22:23The simplest nests are just sticks wedged into position,
0:22:23 > 0:22:26but some are more complicated.
0:22:26 > 0:22:29The long-tailed tit builds a delicate nest
0:22:29 > 0:22:32from plant material and spider silk.
0:22:32 > 0:22:37And weaverbirds do, literally, weave with leaves.
0:22:40 > 0:22:44But are such skills learned or instinctive?
0:22:47 > 0:22:50In 1905, Eugene Marais,
0:22:50 > 0:22:53a South African writer and scientist,
0:22:53 > 0:22:56was intrigued by the complexity of weaverbird nests.
0:22:56 > 0:23:00He wanted to understand more about their nest building skills
0:23:00 > 0:23:03and performed a rigorous, but simple, experiment
0:23:03 > 0:23:05to see if they learnt how to make nests
0:23:05 > 0:23:10or if they built them using what he called "cultural instinct".
0:23:10 > 0:23:14He took eggs from a pair of wild weaverbirds
0:23:14 > 0:23:18and put them into a canary's nest to hatch.
0:23:18 > 0:23:23Then he encouraged the next three generations of weaverbirds to breed,
0:23:23 > 0:23:25but gave them no nest material
0:23:25 > 0:23:28and hatched their eggs, once again, under canaries.
0:23:28 > 0:23:32When nesting time came for the fourth generation of weaverbirds,
0:23:32 > 0:23:34he gave them natural nest materials
0:23:34 > 0:23:36and, without hesitation,
0:23:36 > 0:23:40they vigorously set about constructing perfect wild nests.
0:23:42 > 0:23:47So nest-building is largely under genetic control,
0:23:47 > 0:23:52but it is influenced by experience and the environment.
0:23:52 > 0:23:56Nests of the same kind of weaverbird are not always exactly the same,
0:23:56 > 0:24:01and the birds of necessity must have some flexibility in how they build.
0:24:03 > 0:24:06Nests that hang are particularly difficult to make,
0:24:06 > 0:24:11as the birds have to work against gravity with no support from below.
0:24:11 > 0:24:14Weaverbirds solve part of this problem
0:24:14 > 0:24:16with a skill none others have.
0:24:16 > 0:24:19They're the only birds that can tie knots.
0:24:20 > 0:24:23These knots vary and are worked on until the weaver succeeds
0:24:23 > 0:24:28in attaching several strands of grass to a suitable branch or stem.
0:24:31 > 0:24:33These first fastenings are crucial,
0:24:33 > 0:24:37as the whole of the completed nest will hang from them.
0:24:42 > 0:24:45Once the birds have secured the foundation,
0:24:45 > 0:24:46they can start to weave.
0:24:52 > 0:24:57Weaving is just one way of binding leaves together.
0:24:57 > 0:24:59There are others.
0:25:03 > 0:25:05These are tailorbird nests.
0:25:05 > 0:25:09They consist of folded leaves stuffed with soft material
0:25:09 > 0:25:12and stitched together using spider's silk.
0:25:12 > 0:25:15The tailorbird pierces the leaves with its sharp beak
0:25:15 > 0:25:19and then binds them together by pulling silk through the holes.
0:25:19 > 0:25:24The complete operation involves a number of different skills.
0:25:25 > 0:25:28Making the holes is like riveting.
0:25:28 > 0:25:30Two leaves are placed together
0:25:30 > 0:25:34and then pierced to create matching holes above and below.
0:25:36 > 0:25:39Then the edges are sewn up.
0:25:41 > 0:25:45The upper surface of the leaf is kept to the outside
0:25:45 > 0:25:47to help the nest look unobtrusive.
0:25:50 > 0:25:55The result is a secure pocket, which is then stuffed with a soft lining.
0:26:02 > 0:26:07The materials the birds choose to sew up their nest can vary.
0:26:07 > 0:26:08At the turn of the century,
0:26:08 > 0:26:11there was a report in The Common Birds Of Bombay
0:26:11 > 0:26:14of weaverbirds watching carpet makers and tailors
0:26:14 > 0:26:16as they worked on verandas.
0:26:16 > 0:26:18When the coast was clear,
0:26:18 > 0:26:21the birds flew down and stole tiny pieces of thread
0:26:21 > 0:26:23with which to sew up their nests.
0:26:26 > 0:26:28Birds search with a clear idea
0:26:28 > 0:26:31of what will be suitable nest material.
0:26:31 > 0:26:33Many use sticks and twigs.
0:26:37 > 0:26:40They will, however, occasionally use other material
0:26:40 > 0:26:42that does the same job.
0:26:43 > 0:26:46And their choices are sometimes surprising.
0:26:47 > 0:26:52This nest was found in an aircraft hangar in the 1950s
0:26:52 > 0:26:56and it's made entirely of twisted wire.
0:26:57 > 0:27:01When it was discovered, it contained two blackbird eggs.
0:27:01 > 0:27:03It's an unusual nest for a blackbird,
0:27:03 > 0:27:07but similar nests have been found belonging to crows and pigeons.
0:27:11 > 0:27:14Weaverbirds work with natural material
0:27:14 > 0:27:16and, like the tailorbird,
0:27:16 > 0:27:20they have to solve the problem of joining leaves together.
0:27:20 > 0:27:23After making a knot to secure the basic framework,
0:27:23 > 0:27:25they begin their weaving.
0:27:27 > 0:27:29They construct the main egg chamber
0:27:29 > 0:27:31and then add a small entrance
0:27:31 > 0:27:35around the first securely knotted ring of leaves.
0:27:37 > 0:27:42The male, as he works, is under intense scrutiny.
0:27:43 > 0:27:45Females are looking for mates,
0:27:45 > 0:27:49and males that build firm, well-positioned nests
0:27:49 > 0:27:51are favoured as fathers.
0:27:52 > 0:27:57When he finishes, a male advertises his handiwork by fluttering.
0:27:58 > 0:28:01But he may be forced to build several nests
0:28:01 > 0:28:05before a female finally chooses him as a partner.
0:28:07 > 0:28:10Weaverbirds' nests are very conspicuous.
0:28:11 > 0:28:15Other birds, however, go to some trouble to conceal them.
0:28:18 > 0:28:22We may not have tailorbirds or weaverbirds in Britain,
0:28:22 > 0:28:25but we do have long-tailed tits.
0:28:25 > 0:28:26Delicate little birds
0:28:26 > 0:28:30that make intricate and finely constructed nests.
0:28:33 > 0:28:35With tiny, repetitive movements,
0:28:35 > 0:28:37they use loops of spider's silk
0:28:37 > 0:28:40to fell together their mixture of wool and moss.
0:28:51 > 0:28:54Both male and female work on the construction.
0:28:55 > 0:28:57As the nest takes shape,
0:28:57 > 0:28:59they decorate the outside
0:28:59 > 0:29:03with several thousand tiny flakes of lichen.
0:29:13 > 0:29:16The nest is then lined with hundreds of feathers
0:29:16 > 0:29:19and provides a delicate but strong structure
0:29:19 > 0:29:21to house the growing chicks.
0:29:24 > 0:29:28And it's a nest that's particularly hard to find
0:29:28 > 0:29:30because of its covering of lichen.
0:29:33 > 0:29:36For years, it was believed that this acted as a sort of camouflage
0:29:36 > 0:29:39to help hide the nest.
0:29:39 > 0:29:42But the recent discovery of long-tailed tit nests
0:29:42 > 0:29:45covered with small flakes of paper and polystyrene
0:29:45 > 0:29:50have helped explain more clearly the reason for this decoration.
0:29:50 > 0:29:53Rather than helping to blend the nest with its background,
0:29:53 > 0:29:58these small flakes reflect light from it, making it almost invisible.
0:29:58 > 0:30:03And it seems paper and polystyrene do the job just as well as lichen.
0:30:06 > 0:30:10The largest and, perhaps, the most long-lasting nest of all
0:30:10 > 0:30:13is made by the social weaverbird.
0:30:17 > 0:30:20They live in the dry areas of southern Africa
0:30:20 > 0:30:21and work together
0:30:21 > 0:30:25to build what looks like a great haystack up in a tree.
0:30:27 > 0:30:30New nest chambers are continually added,
0:30:30 > 0:30:33as many as 100 pairs of birds may live together
0:30:33 > 0:30:36under the one roof, as you might say.
0:30:42 > 0:30:46The chambers provide shade during the day
0:30:46 > 0:30:48and keep out the chill at night.
0:30:54 > 0:30:58And the whole construction is so robust
0:30:58 > 0:31:01that it may provide mass housing
0:31:01 > 0:31:03for generation after generation of birds.
0:31:14 > 0:31:18Recently, the biggest nest ever recorded was discovered
0:31:18 > 0:31:22attached to telegraph poles in the Kalahari Desert.
0:31:22 > 0:31:25It's more than seven metres across and three metres high.
0:31:26 > 0:31:30So weaverbirds make their nests in many different ways
0:31:30 > 0:31:34and it was once thought that they worked entirely by instinct,
0:31:34 > 0:31:36but this is not so.
0:31:36 > 0:31:41They are amongst the most expert nest-builders in the animal kingdom,
0:31:41 > 0:31:43and this array of nests
0:31:43 > 0:31:45shows the complex and elaborate designs
0:31:45 > 0:31:47that they can produce.
0:31:47 > 0:31:49Recent studies suggest
0:31:49 > 0:31:52that weaverbirds may be using mental skills
0:31:52 > 0:31:56that are not dissimilar to those required to make simple tools.
0:31:56 > 0:32:00For weaverbirds, a well-built nest is a ticket to successful breeding.
0:32:02 > 0:32:06Who would imagine that such complexity could be produced
0:32:06 > 0:32:09using just a foot and a beak.
0:32:12 > 0:32:15Weaverbirds make their elaborate nests
0:32:15 > 0:32:18from simple materials they find around them.
0:32:18 > 0:32:22Another of nature's extraordinary builders are the spiders.
0:32:22 > 0:32:24They make their complex webs
0:32:24 > 0:32:29from an incredible substance they produce themselves, silk.
0:32:32 > 0:32:34Spider silk is unique.
0:32:34 > 0:32:36It's very thin, very strong,
0:32:36 > 0:32:40and has many exciting potential uses.
0:32:40 > 0:32:41Spiders spin it with ease,
0:32:41 > 0:32:45but scientists have been trying to copy it for many years.
0:32:45 > 0:32:48To do that, we need to understand two of the spider's secrets -
0:32:48 > 0:32:51the exact structure and nature of their silk,
0:32:51 > 0:32:55and the way they transform it from a fluid into a thread.
0:32:57 > 0:33:00Spider silk is a truly remarkable material.
0:33:00 > 0:33:02It can withstand impact
0:33:02 > 0:33:06and it can be strong, stretchy and sticky all at the same time.
0:33:07 > 0:33:11Spiders produce it from special glands inside their bodies
0:33:11 > 0:33:15and extrude it from tiny nipples called spinnerets
0:33:15 > 0:33:18at the back end of their abdomens.
0:33:18 > 0:33:21And what is more, they can produce up to seven different kinds,
0:33:21 > 0:33:23each with its own purpose.
0:33:25 > 0:33:29For centuries, it was the only silk known to man.
0:33:29 > 0:33:32The Ancient Greeks used cobwebs to stop bleeding
0:33:32 > 0:33:37and Australian Aborigines used it to catch small fish.
0:33:37 > 0:33:38Then, in the Far East,
0:33:38 > 0:33:42a different and mysterious new kind of silk started to appear,
0:33:42 > 0:33:45and in much larger quantities.
0:33:46 > 0:33:48According to Chinese legend,
0:33:48 > 0:33:52the first person to weave silk into a fabric
0:33:52 > 0:33:55was the Empress Leizu, back in the 27th century BC.
0:33:56 > 0:34:00She was having tea in her garden under a mulberry tree,
0:34:00 > 0:34:03when a cocoon fell from the branch above
0:34:03 > 0:34:05and dropped into her cup
0:34:05 > 0:34:07and started to unravel.
0:34:07 > 0:34:10Whether that's true or not,
0:34:10 > 0:34:13the Empress Leizu is now honoured as the goddess of silk.
0:34:13 > 0:34:16And silk-moth farming dates back
0:34:16 > 0:34:18to the beginning of Chinese civilisation.
0:34:18 > 0:34:23The silk was traded right across the Near East and into the Roman Empire.
0:34:23 > 0:34:26The Chinese traders were sworn to secrecy
0:34:26 > 0:34:29about how this marvellous material was made.
0:34:29 > 0:34:32But in the year 532,
0:34:32 > 0:34:35the Roman emperor Justinian managed to find out
0:34:35 > 0:34:40that it came not, as some suspected, from a spider's web,
0:34:40 > 0:34:42but from the cocoon of a moth.
0:34:45 > 0:34:48Silk moth caterpillars produce large quantities of silk
0:34:48 > 0:34:52and they make it in a very different way to spiders.
0:34:52 > 0:34:55The caterpillars feed voraciously on mulberry leaves,
0:34:55 > 0:34:59and then, when they're full-grown and ready to transform into a moth,
0:34:59 > 0:35:03they spin silken cocoons in which they will pupate.
0:35:03 > 0:35:06Unlike spiders, which have specialised spinning organs,
0:35:06 > 0:35:10silk moth caterpillars produce silk from their salivary glands.
0:35:12 > 0:35:16Each cocoon is made from a single, unbroken filament,
0:35:16 > 0:35:20that can be over 500 metres long.
0:35:20 > 0:35:24This silk is plentiful and easy to spin commercially,
0:35:24 > 0:35:27but it isn't as tough as spider silk.
0:35:30 > 0:35:35And spider silk also has more exciting potential uses.
0:35:38 > 0:35:39An orb web like this
0:35:39 > 0:35:44is constructed over a Y-shaped scaffold of silk threads,
0:35:44 > 0:35:46which are extremely strong.
0:35:46 > 0:35:51Unlike silkworms, the female spiders, which spin the webs,
0:35:51 > 0:35:53are very territorial and aggressive.
0:35:53 > 0:35:57So farming and collecting spider silk is very difficult,
0:35:57 > 0:35:59but it has been done.
0:36:01 > 0:36:05In 1762, a Spanish missionary called Termeyer
0:36:05 > 0:36:08made a machine that held a single spider,
0:36:08 > 0:36:10from which he pulled a silken thread.
0:36:12 > 0:36:15In London, Daniel Rolt, a factory worker,
0:36:15 > 0:36:18attached spiders to a small steam machine
0:36:18 > 0:36:22and succeeded in reeling out 18 metres of silk a minute.
0:36:22 > 0:36:27That led to machines that were able to milk several spiders at a time.
0:36:31 > 0:36:34Experiments then stopped, until 2004,
0:36:34 > 0:36:37when two textile artists in Madagascar
0:36:37 > 0:36:40built a machine based on these early designs,
0:36:40 > 0:36:43with which they made something very special indeed.
0:36:45 > 0:36:49The golden colour of this stunningly beautiful spider silk shawl
0:36:49 > 0:36:51is completely natural.
0:36:51 > 0:36:54The silk from which it was made
0:36:54 > 0:36:58was produced by 1,063,000 spiders,
0:36:58 > 0:37:01like this one, over four years.
0:37:01 > 0:37:05Local people collected 3,000 spiders a day
0:37:05 > 0:37:08and trained handlers extracted silk
0:37:08 > 0:37:10from groups of 24 at a time.
0:37:10 > 0:37:15After being milked, the spiders were released back into the wild.
0:37:15 > 0:37:19The individual silk strands were then twisted into a thread
0:37:19 > 0:37:23which was woven into this intricately patterned fabric on looms.
0:37:27 > 0:37:29Now, this kind of silk fabric production
0:37:29 > 0:37:31couldn't work commercially.
0:37:31 > 0:37:34Apart from being hard work to make in quantity,
0:37:34 > 0:37:39spider silk isn't really a very suitable thread for fabric.
0:37:39 > 0:37:42As a cloth it reacts badly to moisture and heat,
0:37:42 > 0:37:46but in its natural state, as a single thread,
0:37:46 > 0:37:48it has physical qualities
0:37:48 > 0:37:50that could be exploited medically.
0:37:50 > 0:37:53These special characteristics
0:37:53 > 0:37:58are a consequence of the molecular structure of spider silk.
0:37:58 > 0:38:02It consists of two large protein molecules.
0:38:02 > 0:38:04One is stretchy and spaghetti-like,
0:38:04 > 0:38:07and the other has a harder, crystalline structure.
0:38:07 > 0:38:09Combined, these two proteins
0:38:09 > 0:38:13give silk unique qualities of strength and flexibility.
0:38:15 > 0:38:19Spiders store these proteins as a gel-like liquid in their bodies.
0:38:19 > 0:38:20And when they need to make silk,
0:38:20 > 0:38:23they extrude it through the spinnerets,
0:38:23 > 0:38:25combining the molecules in a special way.
0:38:27 > 0:38:30If we hold down a spider without harming it
0:38:30 > 0:38:32we can see this process in more detail.
0:38:32 > 0:38:37Normally, the spider would attach the end of the silk filament
0:38:37 > 0:38:39to an object and then move away,
0:38:39 > 0:38:42so that the filament is pulled from the spinnerets.
0:38:42 > 0:38:45We can produce the same reaction,
0:38:45 > 0:38:48by gently pulling the end of the filament itself.
0:38:48 > 0:38:51Internally, the silk liquid is passing down a long duct
0:38:51 > 0:38:56in which stretchy elements within the protein molecules
0:38:56 > 0:38:58are lined with harder crystalline ones,
0:38:58 > 0:39:01to create an extremely strong and tough thread.
0:39:04 > 0:39:07Scanning electron microscopes
0:39:07 > 0:39:10reveal how the liquid emerges from the spinnerets.
0:39:10 > 0:39:14Incredibly, spiders can convert liquid proteins
0:39:14 > 0:39:17into a hardened thread at room temperature
0:39:17 > 0:39:19with very little energy.
0:39:19 > 0:39:21If we could understand and copy this process,
0:39:21 > 0:39:25it would be a major scientific breakthrough.
0:39:26 > 0:39:29Scientists have, in fact, spent many years
0:39:29 > 0:39:33trying to replicate the spider's liquid silk and the way it's spun.
0:39:33 > 0:39:37Recently, the genes of spider-silk proteins were cloned
0:39:37 > 0:39:39and put into goats
0:39:39 > 0:39:42to try and produce silk in their milk.
0:39:42 > 0:39:45It worked, and when the goats had kids
0:39:45 > 0:39:49silk proteins were extracted from the mother's milk.
0:39:51 > 0:39:52But none of these processes
0:39:52 > 0:39:57have yet produced silk that is as tough as natural spider silk.
0:39:59 > 0:40:01This machine is called a tensile tester
0:40:01 > 0:40:05and it shows how strong and stretchy spider silk can be.
0:40:05 > 0:40:10This dragline silk is being pulled apart,
0:40:10 > 0:40:13and a graph shows the force the fibre is taking
0:40:13 > 0:40:15and at what point it breaks.
0:40:15 > 0:40:17A steel thread of similar diameter
0:40:17 > 0:40:19would have broken by now.
0:40:25 > 0:40:27There, it's broken.
0:40:27 > 0:40:32Spider silk is the toughest natural material known to man.
0:40:35 > 0:40:37A single thread of web silk,
0:40:37 > 0:40:39less than a millimetre thick,
0:40:39 > 0:40:42can absorb the impact of fast-moving prey
0:40:42 > 0:40:45and bring it to a halt without breaking.
0:40:45 > 0:40:48Complete webs can stretch enormously
0:40:48 > 0:40:51and then return to their original shape
0:40:51 > 0:40:52with a minimum of damage.
0:40:55 > 0:41:00Incredibly, spiders can make this complex material
0:41:00 > 0:41:03from just fresh air, flies and water.
0:41:04 > 0:41:07The best we can do in making a material like it
0:41:07 > 0:41:11requires oil, chemicals and a great deal of energy.
0:41:13 > 0:41:16Although we now better understand the structure of spider silk
0:41:16 > 0:41:19and the natural spinning process,
0:41:19 > 0:41:21we still can't perform the spider's magic
0:41:21 > 0:41:24and copy this extraordinary substance.
0:41:25 > 0:41:29But using small amounts of natural spider silk in clever ways
0:41:29 > 0:41:32has, nonetheless, a very exciting future.
0:41:34 > 0:41:36A sumptuous golden cloth
0:41:36 > 0:41:39is just one possible product.
0:41:40 > 0:41:44This is a dream that has become a reality,
0:41:44 > 0:41:47and shows just how lovely spider silk can be.
0:41:48 > 0:41:51But it also has the potential
0:41:51 > 0:41:53to make other dreams come true.
0:41:53 > 0:41:56It's a biodegradable material
0:41:56 > 0:41:59that we're now using to make artificial joints,
0:41:59 > 0:42:03and it may even help repair damaged spinal tissue.
0:42:04 > 0:42:10This curiosity of nature could, eventually, save lives.