0:00:07 > 0:00:12However well we think we know our planet, the natural world still has
0:00:12 > 0:00:18the ability to surprise us, to shock us, sometimes even to scare us
0:00:18 > 0:00:22with its extraordinary events and bizarre behaviours.
0:00:22 > 0:00:26And given modern technology, nature's weirdest phenomena
0:00:26 > 0:00:32are now frequently caught on camera, wherever and whenever they occur.
0:00:32 > 0:00:35So this means that we can now bring you the strangest
0:00:35 > 0:00:38stories our world has to offer.
0:00:41 > 0:00:44From fish walking out of the water...
0:00:44 > 0:00:48Oh, my gosh! That is blowing my mind!
0:00:48 > 0:00:51..to alien spawn on the sands of South America...
0:00:52 > 0:00:55..and a monster from the ocean depths.
0:00:55 > 0:00:57When I touched it, it just sort of
0:00:57 > 0:01:01felt like a soft, jelly-like substance.
0:01:01 > 0:01:05With the help of eyewitnesses, experts and scientists,
0:01:05 > 0:01:09we're going to try and explain what on earth is going on.
0:01:32 > 0:01:38Nature can astound and confound us and sometimes events can be so
0:01:38 > 0:01:42bizarre that they even challenge the way that we think about our world.
0:01:42 > 0:01:45These incidents can be so extraordinary,
0:01:45 > 0:01:49they even appear to be somewhat supernatural.
0:01:52 > 0:01:54We start with events so unsettling
0:01:54 > 0:01:59they could be seen as omens foretelling the end of days.
0:01:59 > 0:02:01From trees that bleed...
0:02:03 > 0:02:06..to bees making horrifying honey.
0:02:07 > 0:02:11But our first portentous event is in Florida,
0:02:11 > 0:02:15where truly strange behaviour is alarming the locals.
0:02:15 > 0:02:18- What in the world? - How weird is that, huh?
0:02:18 > 0:02:21- It is weird. - Hopping around in the yards...
0:02:21 > 0:02:24My God, where are they coming from?
0:02:24 > 0:02:29Quiet suburban gardens and homes are being overrun.
0:02:29 > 0:02:33- I don't know, that's weird, huh? - We don't know, it's so weird.
0:02:33 > 0:02:37- What are they?- It's fish! - Fish.
0:02:38 > 0:02:43Fish, walking the land. This seems like a very bad sign.
0:02:44 > 0:02:46Look at that one.
0:02:48 > 0:02:51- There's one over there.- Where? - Over there!
0:02:51 > 0:02:55- There's tons of them. - I know, what the...?
0:02:55 > 0:02:58They're not just invading this neighbourhood.
0:02:58 > 0:03:00This is happening all over Florida.
0:03:02 > 0:03:07After a storm, these bizarre fish appear as if from nowhere,
0:03:07 > 0:03:09and every year, their numbers are increasing
0:03:09 > 0:03:11to plague proportions.
0:03:11 > 0:03:15Crawled out through the grass and came out here?
0:03:15 > 0:03:18- Something like that. - There's another one down there.
0:03:18 > 0:03:20- Help.- It's weird.
0:03:20 > 0:03:23- Oh, my gosh!- It's just amazing.
0:03:23 > 0:03:25That is blowing my mind!
0:03:31 > 0:03:34So what on earth are these freaky fish?
0:03:34 > 0:03:36And why have they taken to the streets?
0:03:40 > 0:03:43Feelers which look like whiskers give them away -
0:03:43 > 0:03:46this is a type of catfish.
0:03:46 > 0:03:50But how is this aquatic animal staying alive in air?
0:03:55 > 0:04:00Most fish die if they're out of water for more than a few minutes.
0:04:00 > 0:04:02Their gills can't extract oxygen from the air
0:04:02 > 0:04:04and the fish suffocates.
0:04:06 > 0:04:09But these catfish have a clever adaptation to help them
0:04:09 > 0:04:14breathe out of water, as ecologist and
0:04:14 > 0:04:17fish expert Bill Loftus explains.
0:04:20 > 0:04:23It does this by use of a specialised organ that
0:04:23 > 0:04:25lies behind the gill chamber
0:04:25 > 0:04:30inside of its head, and it can take oxygen from the air through
0:04:30 > 0:04:32that organ and put it into its bloodstream.
0:04:32 > 0:04:35And that's an amazing adaptation for this animal to
0:04:35 > 0:04:38allow it to get out on land and to move around.
0:04:38 > 0:04:42And these fish don't just have the ability to breathe air.
0:04:42 > 0:04:46Oh, no, they've taken life on land one step further.
0:04:47 > 0:04:50They're called walking catfish.
0:04:51 > 0:04:54These piscatorial pedestrians don't just
0:04:54 > 0:04:57flap around wildly like a fish out of water.
0:04:57 > 0:05:00They move with a determined purpose.
0:05:01 > 0:05:04Most fish are only adapted for swimming,
0:05:04 > 0:05:06so how are they walking on land?
0:05:08 > 0:05:12It's all down to the evolution of these front or pectoral fins here,
0:05:12 > 0:05:14which have a rigid spine
0:05:14 > 0:05:16running through them. And this means that they can
0:05:16 > 0:05:19support the front of the fish's body weight and
0:05:19 > 0:05:21when they pivot from side to side
0:05:21 > 0:05:23and thrash vigorously with their tail,
0:05:23 > 0:05:25they move forward.
0:05:25 > 0:05:29It's a bit like us doing a commando crawl, using our elbows,
0:05:29 > 0:05:30pushing with our feet.
0:05:30 > 0:05:33Now, it might sound and look a bit clumsy,
0:05:33 > 0:05:36but it's actually very efficient and it makes these
0:05:36 > 0:05:39things very difficult to stop.
0:05:39 > 0:05:43So why would a fish need to breathe air and walk on land?
0:05:43 > 0:05:47Well, they're not the only fish that leave water.
0:05:48 > 0:05:50A few other species come onto land if the water
0:05:50 > 0:05:54quality deteriorates, or to escape aquatic predators.
0:05:56 > 0:06:00But walking catfish have another, more sinister purpose.
0:06:00 > 0:06:03These fish are on a mission.
0:06:04 > 0:06:07They're hungry and they're out hunting.
0:06:07 > 0:06:09As Florida resident
0:06:09 > 0:06:14and tropical fish breeder Colin Calway discovered to his horror.
0:06:14 > 0:06:17When you're looking at a pond every day, you know the type of fish you
0:06:17 > 0:06:20got in there, and there's a strange activity, something's not right,
0:06:20 > 0:06:22and you've got to find out what it is.
0:06:22 > 0:06:23So we pumped the pond down
0:06:23 > 0:06:27and instead of approximately 10,000 rosy barbs,
0:06:27 > 0:06:31we had - it looked like - 10,000 walking catfish in their place.
0:06:31 > 0:06:35A staggering 10,000 prize specimens became fish food
0:06:35 > 0:06:36almost overnight.
0:06:36 > 0:06:40But that was just the start of the problem.
0:06:40 > 0:06:43These voracious predators eat everything in their path
0:06:43 > 0:06:47and they'll walk a long way to find their prey.
0:06:47 > 0:06:49When they've eaten everything they can in the pond,
0:06:49 > 0:06:52almost wiped it out, they'll wait for that night when a good
0:06:52 > 0:06:56thunderstorm comes or rain comes or very, very heavy dew.
0:06:56 > 0:07:00And then they'll leave the pond in large numbers and they'll
0:07:00 > 0:07:02keep moving up the ditches and through the grass until they find
0:07:02 > 0:07:04another pond.
0:07:04 > 0:07:06Clear that one and they move on again.
0:07:06 > 0:07:10And that pretty well wiped us out as tropical fish farmers.
0:07:10 > 0:07:12But it's not just fish farms.
0:07:14 > 0:07:18Florida's native species are also under attack.
0:07:20 > 0:07:23And the local wildlife isn't adapted to cope.
0:07:23 > 0:07:27You see, walking catfish aren't native to Florida.
0:07:28 > 0:07:33They originally came from Southeast Asia as exotic pets,
0:07:33 > 0:07:36but in the 1960s, a few were released from aquariums
0:07:36 > 0:07:40and now they spread across most of the state.
0:07:40 > 0:07:45For anything in their path, this is a catfish catastrophe.
0:07:45 > 0:07:47Walking catfish are very broad feeders,
0:07:47 > 0:07:52so they will feed on fish, invertebrates, amphibians and
0:07:52 > 0:07:55pretty much the whole gamut of aquatic insects.
0:07:55 > 0:07:58And the devastation on our small native fishes
0:07:58 > 0:08:01and invertebrates is...is just tremendous.
0:08:03 > 0:08:07Walking catfish cause so much destruction, they've actually
0:08:07 > 0:08:12made the list of the top 100 world's worst invaders.
0:08:12 > 0:08:16They've got an arsenal of adaptations for overground invasion.
0:08:16 > 0:08:19They can walk the land, breathe air
0:08:19 > 0:08:24and they're also covered in slime, so they don't dry out.
0:08:24 > 0:08:27And they can survive several months without food.
0:08:27 > 0:08:30So whilst the disturbing sight of
0:08:30 > 0:08:32walking fish isn't a sign of the apocalypse,
0:08:32 > 0:08:36it does spell disaster for local wildlife.
0:08:36 > 0:08:40It's a terrifying takeover, one small step at a time.
0:08:42 > 0:08:46And now, from apocalypse to apocryphal tale. We're going to
0:08:46 > 0:08:49witness an event so alarming,
0:08:49 > 0:08:52it's easy to see why people might think that the
0:08:52 > 0:08:54end of the world is nigh.
0:09:01 > 0:09:06Trees. They've inspired myths and folklore.
0:09:06 > 0:09:09They can be haunting, even eerie.
0:09:09 > 0:09:14Some people even believe that trees have a soul.
0:09:14 > 0:09:17But could they also have a heart and bleed?
0:09:18 > 0:09:21Well, in this incredible event from Australia,
0:09:21 > 0:09:23it certainly looks like it.
0:09:23 > 0:09:25Chris Wharton was chopping down a tree
0:09:25 > 0:09:28when he got the shock of his life.
0:09:28 > 0:09:34Here we have blood pumping out of a tree after I cut it.
0:09:34 > 0:09:38I do not understand why this tree has - apparently -
0:09:38 > 0:09:40blood pumping out of it,
0:09:40 > 0:09:42but the tree itself is still pumping.
0:09:44 > 0:09:49Strangest thing I've ever seen while playing with me chain saw.
0:09:49 > 0:09:52But this isn't an isolated incident.
0:09:52 > 0:09:54All around the world, people are being
0:09:54 > 0:09:57alarmed by blood pouring from trees.
0:09:57 > 0:09:59Look! Look! The tree is bleeding! Look!
0:09:59 > 0:10:01- Looks like blood, though, don't it? - Uh-huh!
0:10:01 > 0:10:05- It does look like blood. - A bleeding tree.
0:10:05 > 0:10:06I got to send this to Steve.
0:10:08 > 0:10:10David Rose is a tree pathologist.
0:10:10 > 0:10:13He's heard reports of these incidents.
0:10:13 > 0:10:17We get quite a few every year, varying from ones where
0:10:17 > 0:10:20people have cut the branch off the tree and it's started to bleed,
0:10:20 > 0:10:23through to ones where the bleeding is coming through what appears to be
0:10:23 > 0:10:25perfectly intact bark.
0:10:25 > 0:10:28And the ones that have got bleeding through the bark, they worry
0:10:28 > 0:10:33about is it a nasty disease, or is it something much more supernatural?
0:10:33 > 0:10:36We had a case in a churchyard in Pembrokeshire where the
0:10:36 > 0:10:40vicar contacted us and he had been driven to distraction by
0:10:40 > 0:10:41numbers of people coming in to see
0:10:41 > 0:10:45this miracle bleeding yew in his churchyard.
0:10:45 > 0:10:50He had people who'd come to see the miracle.
0:10:50 > 0:10:52Yews are amongst our most ancient trees,
0:10:52 > 0:10:55they can live for thousands of years.
0:10:55 > 0:11:01Some revere them as sacred, but morbid myths also surround them.
0:11:01 > 0:11:05Yews are common in churchyards, standing sentinel
0:11:05 > 0:11:09over graves, and they're regularly reported to be bleeding.
0:11:13 > 0:11:18So could the red fluid oozing from these trees really be blood?
0:11:20 > 0:11:24Just like animals, trees have circulation.
0:11:24 > 0:11:26Inside of the body of the tree here
0:11:26 > 0:11:29are many millions of tiny, microscopic vessels which carry
0:11:29 > 0:11:33food and minerals around the tree to help it live and grow.
0:11:34 > 0:11:38Now, there are two basic types. The first, xylem.
0:11:38 > 0:11:43This draws water up from the roots, through the trunk of the tree
0:11:43 > 0:11:49all the way to the top, but importantly, into all of the leaves,
0:11:49 > 0:11:51where it's needed for photosynthesis -
0:11:51 > 0:11:55the process by which the tree produces its food.
0:11:55 > 0:11:58Once it's made that food, a second set of vessels,
0:11:58 > 0:12:03the phloem, transports the food from the leaves to other parts of
0:12:03 > 0:12:07the tree and even all the way down to the roots,
0:12:07 > 0:12:09where it can be stored.
0:12:09 > 0:12:11So if we cut across the trunk,
0:12:11 > 0:12:15that would be a bit like cutting across the limb of an animal.
0:12:15 > 0:12:19You would sever the artery and the fluid would gush out.
0:12:21 > 0:12:24The most extreme bleeding events happen in spring,
0:12:24 > 0:12:29when this fluid, called sap, is rising rapidly in the tree.
0:12:29 > 0:12:32The sap is at high pressure until the leaves
0:12:32 > 0:12:34open and begin to evaporate the water.
0:12:34 > 0:12:38Any injury releases this pressure.
0:12:38 > 0:12:41This apparent bleeding can look distressing,
0:12:41 > 0:12:46but the sap could be the tree's way of trying to heal.
0:12:46 > 0:12:49If you have a disease then it's much thicker
0:12:49 > 0:12:52and often dries to a thick, blackish crust,
0:12:52 > 0:12:57and it contains a lot of antiseptic compounds designed to seal the wound.
0:12:58 > 0:13:02So the sap effectively forms a scab.
0:13:02 > 0:13:05The healing agents in it can cause the red colour.
0:13:05 > 0:13:08Sometimes the sap will also change colour to red
0:13:08 > 0:13:10when it's exposed to the air.
0:13:10 > 0:13:13So that's why it can look like blood.
0:13:15 > 0:13:20Sadly, for some injuries, no amount of healing sap is going to help.
0:13:23 > 0:13:26Tree blood, flowing like a river.
0:13:26 > 0:13:28We cut through an artery there, buddy.
0:13:28 > 0:13:31I don't think he's going to be coming back after this.
0:13:31 > 0:13:34- Try to plug me fingers in. - Go on. Oh, dear.
0:13:40 > 0:13:43Scarlet sap is shocking enough,
0:13:43 > 0:13:47but when something familiar turns a weird colour,
0:13:47 > 0:13:51it can seem like the world has been turned on its head.
0:13:51 > 0:13:55For our next story, we head to the village of Ribeauville, in France.
0:14:00 > 0:14:04The village is set in the beautiful Alsace region.
0:14:04 > 0:14:09Famed for its wine, it also produces a very distinctive type of honey.
0:14:09 > 0:14:13It's famous for its unique flavour, the result of the bees foraging in
0:14:13 > 0:14:16fir trees in the nearby mountains.
0:14:18 > 0:14:21But in 2012, the local beekeepers had a shock.
0:14:22 > 0:14:26When they opened their hives, they found something truly disturbing.
0:14:31 > 0:14:34The bees were making vivid green honey.
0:14:36 > 0:14:38In other hives, it was bright blue.
0:14:42 > 0:14:46In fact to the beekeepers' horror, they found several unusual colours.
0:14:48 > 0:14:52This was unheard of. Some people even wondered if something had
0:14:52 > 0:14:54tipped the very balance of nature.
0:14:55 > 0:14:58And there is cause for concern. You see, bees
0:14:58 > 0:15:01are responsible for pollinating most of our crops.
0:15:01 > 0:15:03If something happened to the bees,
0:15:03 > 0:15:08this could have a catastrophic impact on the whole food chain.
0:15:08 > 0:15:12So this Technicolor turn of events is truly alarming.
0:15:17 > 0:15:21But why would bees make multicoloured honey?
0:15:22 > 0:15:26Well, this isn't the first case of surprising shades of honey.
0:15:26 > 0:15:31It's also happened in a place you might not expect to find a beehive.
0:15:33 > 0:15:38In New York City, beekeeping is an increasingly popular pastime.
0:15:42 > 0:15:46Andrew Cote is head of the New York Beekeepers Association
0:15:46 > 0:15:49and he's been keeping bees since he was a boy.
0:15:49 > 0:15:52Good morning. Honey for you, Miss? No?
0:15:52 > 0:15:55- Too sweet?- Sweet enough?
0:15:55 > 0:15:58Since I've been keeping bees in New York City, I've come across
0:15:58 > 0:16:01bright red, green and blue honey.
0:16:06 > 0:16:08In the city that never sleeps,
0:16:08 > 0:16:13busy bees also make strange honey, although only one colour at a time.
0:16:15 > 0:16:19So is there something about the urban environment that explains it?
0:16:21 > 0:16:26In New York, bees forage for nectar from flowers in parks and gardens.
0:16:29 > 0:16:34Nectar is mostly sugar water and it's the key ingredient of honey.
0:16:36 > 0:16:39The bees take it back to their hive,
0:16:39 > 0:16:42where worker bees pass it around, chewing it.
0:16:43 > 0:16:45They then place it in a cell of their
0:16:45 > 0:16:47honeycomb and buzz their wings
0:16:47 > 0:16:50to evaporate the moisture and the result is honey.
0:16:52 > 0:16:55Different flowers produce slightly different nectar
0:16:55 > 0:16:58and this affects the honey colour,
0:16:58 > 0:17:01normally from pale gold to dark brown.
0:17:01 > 0:17:04But never normally these bright colours.
0:17:07 > 0:17:10In the urban jungle, it's easy to get a sugar fix.
0:17:10 > 0:17:15In our takeaway, fast food world, sugary snacks are everywhere.
0:17:15 > 0:17:19And it's not just us who crave sweet treats.
0:17:19 > 0:17:24Driven by their desire for sugar, the bees are homing in too.
0:17:24 > 0:17:27A friend of mine found that her honey was bright red
0:17:27 > 0:17:30and another fella, he found that his honey was bright red.
0:17:30 > 0:17:33And it turned out that in this little peninsula area of Brooklyn
0:17:33 > 0:17:36called Red Hook, there is a maraschino
0:17:36 > 0:17:41cherry factory that's been there since the 1940s and the bees
0:17:41 > 0:17:43were sipping up the run-off from
0:17:43 > 0:17:45that factory, and when there's
0:17:45 > 0:17:49a concentrated, sugary syrup that's just ready to be picked up,
0:17:49 > 0:17:52it's very hard for the bee to resist.
0:17:52 > 0:17:55Like it would be hard for a child to resist snack food, junk food.
0:17:55 > 0:17:58There are accounts of it happening in England,
0:17:58 > 0:18:02bees going near a Coca-Cola bottling plant and producing
0:18:02 > 0:18:05some kind of sickly, sweet nectar.
0:18:06 > 0:18:09So what about Andrew's green honey?
0:18:09 > 0:18:11I really don't know what produced that green honey,
0:18:11 > 0:18:13I think it was probably antifreeze.
0:18:13 > 0:18:17Whilst it's toxic to us, antifreeze is incredibly sweet,
0:18:17 > 0:18:20and bees are attracted to the scent.
0:18:20 > 0:18:23So in their relentless hunt for sugar,
0:18:23 > 0:18:25these industrious insects are making
0:18:25 > 0:18:27a bee-line for anything sweet,
0:18:27 > 0:18:32and what they find can be very brightly coloured indeed.
0:18:32 > 0:18:36And once one bee from a colony finds it, they all will.
0:18:36 > 0:18:39When they return from their foraging trips, bees perform
0:18:39 > 0:18:42a "waggle dance", which gives others the exact
0:18:42 > 0:18:45direction and distance to the food source.
0:18:45 > 0:18:51So, before long, the whole hive is filled with strange-coloured honey.
0:18:51 > 0:18:54But should we eat it?
0:18:54 > 0:18:57It depends on how experimental the person is.
0:18:57 > 0:19:01I don't think it's necessarily a good idea to try an odd-coloured
0:19:01 > 0:19:06honey, or drink a plutonium milkshake, or do anything risky.
0:19:06 > 0:19:11It can't be sold as food, only as a curiosity item.
0:19:11 > 0:19:13I think it happens especially in New York
0:19:13 > 0:19:16because we're living in such close proximity to
0:19:16 > 0:19:19one another, even our bees are right in our midst.
0:19:19 > 0:19:24Brightly coloured honey might be disturbing to us but for urban bees,
0:19:24 > 0:19:28using whatever sugar they can find makes perfect sense.
0:19:28 > 0:19:32So this funny honey isn't a sign of the end of days,
0:19:32 > 0:19:35it's a sign of our changing times.
0:19:37 > 0:19:41But what about those French bees, living out in the countryside?
0:19:41 > 0:19:47How did they create honey in such a range of bright colours?
0:19:47 > 0:19:49Well, it turned out that they were flying
0:19:49 > 0:19:53a couple of miles across the fields to a waste reprocessing plant,
0:19:53 > 0:19:57where they were feeding on the discarded husks of M&M's.
0:19:57 > 0:19:59So it turns out
0:19:59 > 0:20:02that it was a pot of man-made sugar that was providing
0:20:02 > 0:20:04all the colours of the rainbow.
0:20:04 > 0:20:09What these stories reveal is that events we might read as signs
0:20:09 > 0:20:15of the apocalypse may actually be nature's survival strategies.
0:20:15 > 0:20:18Whether it's a fish taking over new territory,
0:20:18 > 0:20:21healing sap pouring from trees,
0:20:21 > 0:20:24or streetwise bees on a sugar rush.
0:20:27 > 0:20:30Far from signalling the end of the world, we are seeing nature
0:20:30 > 0:20:34working in a perfect but rather peculiar way.
0:20:37 > 0:20:41Next, it's time to meet animals which have formed unexpected
0:20:41 > 0:20:42and bizarre bonds.
0:20:44 > 0:20:47Like the cat rearing a remarkable litter.
0:20:49 > 0:20:53Or a sea creature that's more than the sum of its parts.
0:20:57 > 0:21:01But first, we travel to the Azores, islands in the Atlantic Ocean.
0:21:03 > 0:21:06In September 2011, marine biologists took to the
0:21:06 > 0:21:08high seas in search of whales.
0:21:10 > 0:21:13On a typical day, we would go out into the open water
0:21:13 > 0:21:17and we would look for plumes of misty vapour.
0:21:17 > 0:21:19From the surface, you can only get a little
0:21:19 > 0:21:21bit of a glimpse of what's happening beneath the surface.
0:21:21 > 0:21:23It's kind of like an iceberg, you know?
0:21:23 > 0:21:2680% of the action is actually below the surface.
0:21:26 > 0:21:28Dr Alexander Wilson
0:21:28 > 0:21:31is a research associate from Carlton University in Canada.
0:21:35 > 0:21:39And what he experienced that day came completely out of the blue.
0:21:40 > 0:21:44He was filming this pod of sperm whales,
0:21:44 > 0:21:46the world's largest predators.
0:21:46 > 0:21:49They come to these waters to rear their calves.
0:21:50 > 0:21:54But there was something very surprising about this family.
0:21:55 > 0:21:58A bottlenose dolphin was swimming with them.
0:22:00 > 0:22:02The dolphin was a very unique animal.
0:22:02 > 0:22:05He was a full-grown adult male in very good condition
0:22:05 > 0:22:07from what we could tell.
0:22:07 > 0:22:11But he obviously had this very visible spinal malformation.
0:22:11 > 0:22:13Despite its birth defect,
0:22:13 > 0:22:17the dolphin was keeping pace with the whales and remarkably,
0:22:17 > 0:22:20it seemed to be deliberately interacting with them.
0:22:23 > 0:22:28The dolphin tended to use its tail flukes, its flippers
0:22:28 > 0:22:31and dorsal fin, as well as nuzzling with the sperm whales.
0:22:31 > 0:22:33And the whales were responding.
0:22:33 > 0:22:35They would roll around
0:22:35 > 0:22:39and rub their sides along the body of the dolphin and this is
0:22:39 > 0:22:43a type of behaviour that they also demonstrated to each other.
0:22:43 > 0:22:47Close interaction between dolphins and sperm whales
0:22:47 > 0:22:51is almost unheard of, and this is the first time it's been filmed.
0:22:55 > 0:23:00So, why would two such different species keep such close company?
0:23:04 > 0:23:06Well, there are a few other examples
0:23:06 > 0:23:10where different species club together.
0:23:10 > 0:23:13In India, chital deer often graze alongside
0:23:13 > 0:23:17langur monkeys, so there are more eyes looking out for danger.
0:23:20 > 0:23:23The deer even recognise the monkey's alarm calls,
0:23:23 > 0:23:26helping them to make a quick getaway.
0:23:36 > 0:23:40So is this why the dolphin decided to swim with the sperm whales?
0:23:40 > 0:23:44Did these massive marine mammals provide protection?
0:23:44 > 0:23:48Given that there's not very many predators that are capable of
0:23:48 > 0:23:51feeding on such a large dolphin in the area,
0:23:51 > 0:23:53this is unlikely to be a sole explanation.
0:23:53 > 0:23:56But we did see them interacting in a very friendly way,
0:23:56 > 0:23:59making a lot of physical contact, and so it seems to
0:23:59 > 0:24:03suggest that some kind of underlying social factor is involved.
0:24:03 > 0:24:06And this would make sense for our dolphin.
0:24:09 > 0:24:13Dolphins are exceptionally sociable animals.
0:24:13 > 0:24:15They usually live in groups of up to 100.
0:24:17 > 0:24:20Sometimes, their pods will even merge for a while,
0:24:20 > 0:24:25forming spectacular schools up to 6,000 strong.
0:24:29 > 0:24:32Dolphins often work together to catch food
0:24:32 > 0:24:36and social interaction is an important part of their daily lives.
0:24:38 > 0:24:43So why was our dolphin all on his own?
0:24:43 > 0:24:44It's highly probable
0:24:44 > 0:24:46that the fact that this dolphin did have a very unique
0:24:46 > 0:24:51spinal malformation was part of the reason for this type of interaction.
0:24:51 > 0:24:54In dolphin groups, they exhibit a very strong hierarchy
0:24:54 > 0:24:56and this dolphin - for some reason -
0:24:56 > 0:24:59might have been lower on the totem pole than other members.
0:24:59 > 0:25:01And could have been picked on by group members.
0:25:01 > 0:25:05So this dolphin may have been deserted by its own pod.
0:25:07 > 0:25:11Like us, dolphins find isolation very stressful.
0:25:13 > 0:25:17Lonely dolphins may even seek out other species for company.
0:25:18 > 0:25:21And they don't even have to be marine animals.
0:25:23 > 0:25:25A few years ago in Ireland,
0:25:25 > 0:25:29a dolphin forged a friendship with a local dog.
0:25:29 > 0:25:32The dog and the dolphin would meet almost every day
0:25:32 > 0:25:37in Tory Island Harbour and they spent many hours together.
0:25:40 > 0:25:44So if our dolphin had been abandoned, maybe
0:25:44 > 0:25:48he sought out the sperm whales.
0:25:48 > 0:25:52But there's more beneath the surface of this story.
0:25:52 > 0:25:56You see, it's the first time that anyone has ever seen sperm whales
0:25:56 > 0:26:00interacting with another species like this.
0:26:00 > 0:26:03Sperm whales aren't known to associate with any other species,
0:26:03 > 0:26:05it's never been seen before.
0:26:05 > 0:26:10This is so unusual, we can only speculate on why they're doing it.
0:26:10 > 0:26:15Perhaps the whales mistook the dolphin for one of their own.
0:26:15 > 0:26:18Sperm whale calves are about four metres long at birth,
0:26:18 > 0:26:21about the same size as this dolphin,
0:26:21 > 0:26:24and the whales were touching the dolphin
0:26:24 > 0:26:27in the way that they would touch their calves.
0:26:27 > 0:26:30But there's another intriguing possibility.
0:26:31 > 0:26:36For centuries, humans have believed that whales can display emotion.
0:26:36 > 0:26:39Indeed, they've been revered as spirit animals in many cultures.
0:26:39 > 0:26:41But now recent research has shown
0:26:41 > 0:26:45that they can display empathy, a care for others.
0:26:45 > 0:26:49Examinations of the brains of certain species of whale and dolphin
0:26:49 > 0:26:52have shown that they have the types of neurons
0:26:52 > 0:26:55typically associated with social organisation,
0:26:55 > 0:26:59speech and recognising suffering in other animals.
0:26:59 > 0:27:02So it seems that science is finally catching up
0:27:02 > 0:27:06with ancient-held beliefs that we're not the only ones out there
0:27:06 > 0:27:08that care for other animals.
0:27:08 > 0:27:12So it might just be that the whales were caring for the dolphin
0:27:12 > 0:27:17and for his part, the dolphin was seeking out their company.
0:27:18 > 0:27:20Whatever was going on here,
0:27:20 > 0:27:23there's no doubt that this was a truly unique encounter.
0:27:27 > 0:27:30These two marine mammals forged an unlikely bond,
0:27:30 > 0:27:35but some animals create even freakier extended families.
0:27:37 > 0:27:40Nothing could be stronger than the connection
0:27:40 > 0:27:42between a mother and her young.
0:27:44 > 0:27:46Big cats are devoted parents,
0:27:46 > 0:27:50and their domestic cousins are no less attentive.
0:27:50 > 0:27:54But in some feline families, the laws of nature
0:27:54 > 0:27:57seem to get turned on their head.
0:27:59 > 0:28:03This is Sonya, a cat from central Russia,
0:28:03 > 0:28:05who's taken motherhood to the extreme.
0:28:07 > 0:28:10These three baby hedgehogs were orphaned
0:28:10 > 0:28:13and wouldn't have survived on their own.
0:28:13 > 0:28:15But incredibly, Sonya adopted them
0:28:15 > 0:28:19and suckled them as if they were her own kittens.
0:28:20 > 0:28:24But remarkably, cats have adopted other small mammals,
0:28:24 > 0:28:26like rabbits and squirrels.
0:28:28 > 0:28:31And take the case of the cat in Ireland
0:28:31 > 0:28:34that adopted three tiny ducklings.
0:28:34 > 0:28:37She was rearing them with her own kittens.
0:28:37 > 0:28:40Birds normally feature high on a cat's menu,
0:28:40 > 0:28:46so to see this cat being so gentle with these baby birds is remarkable.
0:28:53 > 0:28:57So why are these cats suppressing their natural hunting instincts
0:28:57 > 0:28:59to look after other species?
0:29:01 > 0:29:02Well, in the wild,
0:29:02 > 0:29:07lionesses sometimes care for cubs that aren't their own.
0:29:07 > 0:29:10Forming a cub creche helps them share the workload of hunting
0:29:10 > 0:29:12and suckling the cubs.
0:29:17 > 0:29:22So cats can have a flexible approach to childcare.
0:29:22 > 0:29:24But why would they adopt an animal
0:29:24 > 0:29:26from a completely different species?
0:29:28 > 0:29:31Most mammals give birth to small, vulnerable babies,
0:29:31 > 0:29:34completely dependent on their mother.
0:29:34 > 0:29:37A strong bond between them is vital.
0:29:37 > 0:29:41When a mammal gives birth and then suckles her young,
0:29:41 > 0:29:46she's affected by a powerful hormone called oxytocin
0:29:46 > 0:29:50and this promotes feelings of love and bonding.
0:29:50 > 0:29:52Whenever domestic cats adopt other species,
0:29:52 > 0:29:57it turns out they've recently had their own kittens.
0:29:57 > 0:29:59A slave to their hormones,
0:29:59 > 0:30:04they're primed to care for young animals, any young animals.
0:30:04 > 0:30:07Just a few days later, and they wouldn't have taken them in.
0:30:07 > 0:30:10In fact, they might have eaten them.
0:30:10 > 0:30:14So this explains why cats might adopt another species,
0:30:14 > 0:30:16but what about those ducklings?
0:30:16 > 0:30:22Surely they should have been afraid of a potential predator like a cat?
0:30:22 > 0:30:26Well, for them, there was another powerful instinct at work.
0:30:32 > 0:30:35In the 1930s, an Austrian scientist, Konrad Lorenz,
0:30:35 > 0:30:38discovered a strange phenomenon.
0:30:38 > 0:30:42Lorenz worked with young goslings and found that,
0:30:42 > 0:30:46if he was the first thing they saw after hatching,
0:30:46 > 0:30:48they would follow him like a parent.
0:30:48 > 0:30:51They had "imprinted" on him.
0:30:52 > 0:30:56So this could explain how our ducklings bonded to the cat.
0:30:56 > 0:31:00But why does imprinting happen in the first place?
0:31:06 > 0:31:10Well, birds that nest on the ground are vulnerable to predators,
0:31:10 > 0:31:12so their chicks have to be on the move
0:31:12 > 0:31:14as soon as they've hatched.
0:31:16 > 0:31:20It's vital that they follow their parents
0:31:20 > 0:31:22and don't wander off into danger,
0:31:22 > 0:31:26and that's where imprinting comes in.
0:31:26 > 0:31:28There you go.
0:31:28 > 0:31:32So imprinting is an amazing survival mechanism
0:31:32 > 0:31:36whereby sensory information is "stamped"
0:31:36 > 0:31:40into the brain of tiny, vulnerable and mobile young,
0:31:40 > 0:31:42like these ducklings.
0:31:42 > 0:31:44Then they're best placed to recognise those
0:31:44 > 0:31:48who are responsible for feeding them and protecting them.
0:31:48 > 0:31:51But imprinting is quite unbiased.
0:31:51 > 0:31:54Movement, smell and sound are important,
0:31:54 > 0:31:55but if I'm honest with you,
0:31:55 > 0:31:58the imprinted object doesn't even need to be alive
0:31:58 > 0:32:02and in the past, young animals like these ducklings
0:32:02 > 0:32:06have imprinted upon watering cans, robots,
0:32:06 > 0:32:11even plastic milk bottles tied to the back of electric toy trains.
0:32:11 > 0:32:15So when a duckling imprints upon a human, or a cat,
0:32:15 > 0:32:17it's nothing personal.
0:32:17 > 0:32:21They might have even imprinted on a pair of wellingtons.
0:32:21 > 0:32:25So in the strange case of the cat and the ducklings,
0:32:25 > 0:32:27it was all down to timing.
0:32:27 > 0:32:33The cat was flooded with hormones which made her bond with the ducks,
0:32:33 > 0:32:37whilst the ducks, being so young, imprinted on her.
0:32:38 > 0:32:41After a few weeks, they went their separate ways.
0:32:42 > 0:32:44That's the reason behind
0:32:44 > 0:32:47the most unorthodox foster families on the planet.
0:32:51 > 0:32:55It's strange to see a bond between natural born enemies.
0:32:55 > 0:32:58But some close relationships are even weirder.
0:32:59 > 0:33:01Next, we travel to Tasmania,
0:33:01 > 0:33:05where divers discovered something very unusual.
0:33:06 > 0:33:10We went off down with another couple of guys on the boat
0:33:10 > 0:33:13to jump in and film some seals.
0:33:13 > 0:33:17What Mick Baron saw next took him completely by surprise.
0:33:19 > 0:33:21Well, I jumped in the water first
0:33:21 > 0:33:24and then my camera was passed down to me and while I was setting it up,
0:33:24 > 0:33:29I saw this strange animal about 30 metres away.
0:33:29 > 0:33:32I thought, "Wow! What's this?" So I yelled out
0:33:32 > 0:33:35to the other two guys on the boat, "Come on, guys. Get in here,
0:33:35 > 0:33:39"you've got something here you'll never see again in your life."
0:33:44 > 0:33:48An enormous, tube-shaped structure was hanging in the water.
0:33:50 > 0:33:53It was about ten metres long.
0:33:53 > 0:33:55When I touched it, it didn't actually react,
0:33:55 > 0:33:59it just sort of felt like a soft, jelly-like substance.
0:34:00 > 0:34:05And strangest of all, the tube was glowing with an eerie blue light.
0:34:06 > 0:34:09Was its origin even alien?
0:34:10 > 0:34:13I've been diving for quite a long time, say, 40 years,
0:34:13 > 0:34:15and when I saw this one, I thought,
0:34:15 > 0:34:18"Wow! This is a pretty unusual experience."
0:34:24 > 0:34:29So what was this gigantic, glowing tube? And was it even alive?
0:34:31 > 0:34:35When it comes to the ocean, we've barely scratched the surface.
0:34:36 > 0:34:38It's often said that the deep sea
0:34:38 > 0:34:41is Earth's last unexplored frontier.
0:34:43 > 0:34:45Teeming with alien-looking life.
0:34:46 > 0:34:50But even these bizarre creatures have features we can recognise.
0:34:53 > 0:34:54Eyes.
0:34:54 > 0:34:56Limbs.
0:34:57 > 0:34:58Teeth.
0:35:00 > 0:35:05The thing the divers encountered had none of these.
0:35:05 > 0:35:07But there is another possibility.
0:35:09 > 0:35:12You see, some marine animals live together,
0:35:12 > 0:35:15forming a much bigger organism.
0:35:17 > 0:35:19Take coral reefs.
0:35:19 > 0:35:22Corals are formed by colonies of creatures known as polyps.
0:35:24 > 0:35:28These tiny animals build a hard exoskeleton around them.
0:35:30 > 0:35:32And living together in their billions,
0:35:32 > 0:35:34they form some of the world's largest
0:35:34 > 0:35:36and most spectacular structures.
0:35:38 > 0:35:41Like the Great Barrier Reef.
0:35:41 > 0:35:46And it's not just corals that take to communal living.
0:35:46 > 0:35:51Our giant tube is actually a colony of tiny animals,
0:35:51 > 0:35:53known as a pyrosome.
0:35:55 > 0:35:59Rebecca Helm is a research graduate at Brown University.
0:35:59 > 0:36:02She's been studying these strange creatures.
0:36:02 > 0:36:06Pyrosomes are made up of tens to thousands of clones
0:36:06 > 0:36:08of very small-bodied animals,
0:36:08 > 0:36:12and these clones all stick together to each other
0:36:12 > 0:36:17with shared tissues and form this large, tube-shaped colony of animals.
0:36:17 > 0:36:19Pyrosomes are usually clear.
0:36:19 > 0:36:22They can be kind of a reddish pink, even,
0:36:22 > 0:36:26and they can most of the time get to a couple of centimetres,
0:36:26 > 0:36:29but the largest ones can get up to 20 metres.
0:36:30 > 0:36:35This particular pyrosome was one of the largest ever caught on camera.
0:36:37 > 0:36:40Together, these tiny creatures cruise the oceans
0:36:40 > 0:36:42as one colossal structure.
0:36:43 > 0:36:47They prefer warm waters close to the surface
0:36:47 > 0:36:50and the tubular shape helps the animals move.
0:36:50 > 0:36:53You see, each individual takes in water
0:36:53 > 0:36:56which it squirts into the hollow centre,
0:36:56 > 0:36:59moving the whole colony by jet propulsion.
0:37:00 > 0:37:03Although the tube has a man-sized opening at one end,
0:37:03 > 0:37:05they aren't dangerous to us.
0:37:07 > 0:37:10Pyrosomes are filter-feeders,
0:37:10 > 0:37:14which feast on micro-organisms like plankton and bacteria.
0:37:15 > 0:37:18Sometimes animals do find their way inside by accident,
0:37:18 > 0:37:19like this shrimp.
0:37:24 > 0:37:26But what about that eerie glowing?
0:37:28 > 0:37:32Well, the Greek word "pyro" means "fire".
0:37:32 > 0:37:35And this is bioluminescence.
0:37:35 > 0:37:39It acts as a warning sign that a predator might be about.
0:37:40 > 0:37:44Pyrosomes are incredibly bioluminescent.
0:37:44 > 0:37:48Bioluminescence is the ability of an organism to produce light
0:37:48 > 0:37:49using a mixture of chemicals
0:37:49 > 0:37:52that they keep in separate compartments in their body,
0:37:52 > 0:37:55and then when the time is right, kind of like a glowstick,
0:37:55 > 0:37:58they mix them all together, and that creates a luminescence.
0:38:01 > 0:38:0580-90% of deep-sea creatures are bioluminescent.
0:38:08 > 0:38:13They usually glow green or blue, colours that travel well in water.
0:38:14 > 0:38:18And pyrosomes are some of the brightest animals in the ocean.
0:38:20 > 0:38:24These communities truly are wonders of nature.
0:38:26 > 0:38:29A "superorganism" of tiny animals working as one.
0:38:30 > 0:38:35A pyrosome really is greater than the sum of its parts.
0:38:37 > 0:38:41In these extraordinary stories, we've seen what happens
0:38:41 > 0:38:43when animals forge relationships
0:38:43 > 0:38:46beyond the normal boundaries of biology,
0:38:46 > 0:38:50whether it's a lonely dolphin finding new friends,
0:38:50 > 0:38:54cats adopting animals that should be dinner...
0:38:54 > 0:38:59or a colony of tiny creatures which live and glow together.
0:38:59 > 0:39:03When some animals get together, the results can be truly bizarre.
0:39:07 > 0:39:11Finally, we investigate stories so strange,
0:39:11 > 0:39:15many think there's an extra-terrestrial explanation.
0:39:15 > 0:39:18From the mystery of the droning sand dunes...
0:39:18 > 0:39:19Wow.
0:39:21 > 0:39:24..to alien spawn on our beaches.
0:39:28 > 0:39:32But for our first "alien invasion", we head to Central Canada.
0:39:34 > 0:39:39The city of North Battleford. Population, 14,000,
0:39:39 > 0:39:42and usually a pretty peaceful place to live.
0:39:42 > 0:39:49But in January 2012, as night fell, things got very strange indeed,
0:39:49 > 0:39:53as the town was terrorised by earth-shattering noises,
0:39:53 > 0:39:56and they were coming from the sky.
0:39:59 > 0:40:04EERIE HORN-LIKE SOUND
0:40:08 > 0:40:10NOISE CONTINUES
0:40:14 > 0:40:18LOUD, DISCORDANT NOISE
0:40:24 > 0:40:30Me and Tommy are hearing noises. Trumpets.
0:40:32 > 0:40:35This town is having strange things going on.
0:40:36 > 0:40:37Yep.
0:40:40 > 0:40:44LOUD TRUMPETING CONTINUES
0:40:46 > 0:40:50After a sleepless night straight from a sci-fi movie,
0:40:50 > 0:40:52the residents of North Battleford were worried.
0:40:52 > 0:40:55People were kind of mildly talking about it,
0:40:55 > 0:40:57but no-one really wanting to sound like they were crazy!
0:40:57 > 0:41:00People were phoning in, they were phoning in to the police,
0:41:00 > 0:41:04they were phoning in to various agencies asking what was going on.
0:41:05 > 0:41:07So it frightened people.
0:41:07 > 0:41:10It was very disturbing. It was really chilling to hear
0:41:10 > 0:41:13and to know that everybody else was hearing it as well.
0:41:13 > 0:41:17It kind of sounded like there was a transformer right outside my window.
0:41:19 > 0:41:23Literally sounded like trumpets playing from the sky.
0:41:26 > 0:41:30With no obvious explanation for these alien acoustics,
0:41:30 > 0:41:32the rumours ran wild.
0:41:32 > 0:41:36We heard all kinds of things, electromagnetic waves.
0:41:36 > 0:41:38Echoes, because of ice moving in the Arctic.
0:41:38 > 0:41:39Alien invasions.
0:41:39 > 0:41:41Cars sliding on the train tracks.
0:41:41 > 0:41:43Maybe snow clearing.
0:41:43 > 0:41:47But this story gets stranger, because as it turns out,
0:41:47 > 0:41:50events just like this are happening all around the world.
0:41:52 > 0:41:56Was it an elaborate prank, the sound of aliens, or something else?
0:42:04 > 0:42:07Reports of extra-terrestrial sounds from the sky
0:42:07 > 0:42:11are hitting the headlines across the planet.
0:42:11 > 0:42:13METALLIC WHINING
0:42:22 > 0:42:24LOUD METALLIC WHINING
0:42:34 > 0:42:39In some places, the noises are so loud, they set off car alarms.
0:42:39 > 0:42:42CAR ALARM BLARES IN DISTANCE
0:42:47 > 0:42:50So is this the start of a close encounter?
0:42:50 > 0:42:54What were the unnerving noises heard in North Battleford?
0:42:58 > 0:43:03Trevor Cox is a professor of acoustics at Salford University.
0:43:03 > 0:43:05There's lots of examples of unexplained sounds,
0:43:05 > 0:43:08which usually, in the end, you can find some cause for.
0:43:08 > 0:43:11I mean, little earthquakes can cause low frequency sounds
0:43:11 > 0:43:12that people can hear,
0:43:12 > 0:43:16or you might have the distant sounds of things like thunder.
0:43:16 > 0:43:19It's unlikely that this would directly explain
0:43:19 > 0:43:21the sounds in North Battleford,
0:43:21 > 0:43:24as no earthquakes or storms were recorded that day.
0:43:24 > 0:43:27But could the weather be a clue?
0:43:27 > 0:43:31There is a connection between many of the events.
0:43:31 > 0:43:33They happened in winter,
0:43:33 > 0:43:38and it turns out that temperature has a strange effect on sound.
0:43:40 > 0:43:42Now, we all know that hot air rises,
0:43:42 > 0:43:47but I can demonstrate that property using this coloured water.
0:43:47 > 0:43:50I've got warm yellow water in the bottom bottle here,
0:43:50 > 0:43:53and cold blue water in the one at the top,
0:43:53 > 0:43:55and just look at what happens
0:43:55 > 0:43:59if I pull this piece of plastic which is keeping them apart away.
0:44:00 > 0:44:04Immediately, we get mixing.
0:44:04 > 0:44:08On occasions, though, when the ground is so cold,
0:44:08 > 0:44:11a layer of cold air is trapped beneath a layer of warm air.
0:44:11 > 0:44:17So again, cool blue water here and the yellow warm water at the top,
0:44:17 > 0:44:22and this time, if I remove the plastic really carefully,
0:44:22 > 0:44:27you can see that there is no mixing.
0:44:27 > 0:44:32Now, what's interesting is that when sound is moving through air,
0:44:32 > 0:44:34it moves more rapidly through warm air
0:44:34 > 0:44:36than it does through cool air.
0:44:36 > 0:44:40Sound waves normally travel up in straight lines
0:44:40 > 0:44:43and disappear into the atmosphere, but in this case
0:44:43 > 0:44:46they hit that barrier of warm air
0:44:46 > 0:44:48and then are bent back down to the earth,
0:44:48 > 0:44:53and this means they can travel great distances from the point of origin.
0:44:53 > 0:44:56So although the alarming sounds in North Battleford
0:44:56 > 0:44:58appeared to have come from the sky,
0:44:58 > 0:45:04the source was probably on the ground, hundreds of miles away.
0:45:04 > 0:45:09But that doesn't explain why many of the noises were so otherworldly.
0:45:09 > 0:45:12Grating, droning, trumpeting -
0:45:12 > 0:45:16it's the soundtrack to an alien insurrection.
0:45:16 > 0:45:20So what explains the extra-terrestrial acoustics?
0:45:20 > 0:45:22By the time you've heard these sounds,
0:45:22 > 0:45:23they will have travelled a long distance
0:45:23 > 0:45:25and the high frequencies will have been lost,
0:45:25 > 0:45:29just by absorption in the air, so all they're hearing is the low frequency.
0:45:29 > 0:45:31So they're going to sound a bit odd. It's a bit like
0:45:31 > 0:45:34you've taken a recording and put it through a graphic equalizer
0:45:34 > 0:45:36and you've only got the bass left.
0:45:36 > 0:45:40So this explains why these noises sound so alien
0:45:40 > 0:45:46and this could happen anywhere, if the conditions are right.
0:45:46 > 0:45:49Really loud sound waves can travel huge distances
0:45:49 > 0:45:50and the best example in the UK
0:45:50 > 0:45:53is probably the Buncefield oil depot which blew up a few years back,
0:45:53 > 0:45:56and that sound travelled all the way to Holland.
0:45:56 > 0:45:57It was actually heard 200 miles away.
0:45:57 > 0:46:00So the sound waves which normally would be going upwards
0:46:00 > 0:46:03were bent down and were heard all the way over in Belgium and Holland.
0:46:03 > 0:46:06If I was going to guess, the most likely cause of the noise in Canada
0:46:06 > 0:46:08was probably some industrial machinery,
0:46:08 > 0:46:11rather than being some sort of weird UFO effect.
0:46:12 > 0:46:14We may never know what actually made
0:46:14 > 0:46:17the strange noises in North Battleford
0:46:17 > 0:46:19because the source was so far away.
0:46:21 > 0:46:24But it was likely to have been man-made and mechanical.
0:46:26 > 0:46:31So although more disturbed nights might lie ahead,
0:46:31 > 0:46:35the residents of North Battleford now know the aliens aren't invading.
0:46:38 > 0:46:39At least, not yet.
0:46:42 > 0:46:47So physics can account for nerve-racking noises from the sky.
0:46:47 > 0:46:49But what about strange sounds
0:46:49 > 0:46:52coming from beneath the surface of the earth?
0:46:55 > 0:46:59For centuries, travellers have told tales of eerie sounds in the desert.
0:47:01 > 0:47:04But these are foreboding and extreme landscapes...
0:47:08 > 0:47:10..where your mind can play tricks.
0:47:10 > 0:47:16And until recently, these tales were only whispers on the wind.
0:47:18 > 0:47:21Today, deserts are far more accessible
0:47:21 > 0:47:25and now people have started recording these strange sounds.
0:47:25 > 0:47:28LOUD DRONING
0:47:31 > 0:47:32Wow!
0:47:36 > 0:47:39They're hearing deep, droning noises in the dunes.
0:47:43 > 0:47:49We're in Doha, Qatar. The ground is shaking.
0:47:49 > 0:47:51It's vibrating!
0:47:51 > 0:47:54In the Gobi desert in China, to the Namib in Africa
0:47:54 > 0:48:00and deserts in North America, people are hearing unearthly sounds.
0:48:00 > 0:48:01The sound is very, very loud,
0:48:01 > 0:48:06I would say standing next to a bass in a rock concert, it's dead loud.
0:48:06 > 0:48:09And it seems to be coming from the desert itself.
0:48:09 > 0:48:12When you're sliding down the dune, your whole body starts to vibrate
0:48:12 > 0:48:15and you are really wondering where the sound is coming from,
0:48:15 > 0:48:18but it's from underneath you.
0:48:18 > 0:48:23Something inside the dune is making earth-shaking sounds.
0:48:27 > 0:48:32So what's hiding inside these dunes, and creating this deafening drone?
0:48:34 > 0:48:36Some of these dunes are vast.
0:48:36 > 0:48:39Something large could easily be hidden inside.
0:48:39 > 0:48:41For more than 100 years,
0:48:41 > 0:48:46scientists have been trying to find the source of these sounds.
0:48:46 > 0:48:49And finally, after decades of speculation,
0:48:49 > 0:48:53one team might have unearthed the secret of the dunes.
0:48:53 > 0:48:58Dr Nathalie Vriend is part of a team working in the California deserts.
0:48:58 > 0:49:00When we're doing our research,
0:49:00 > 0:49:02we're measuring the sound frequency with a microphone.
0:49:04 > 0:49:06And we're also measuring
0:49:06 > 0:49:08the internal structure of the dune with radar.
0:49:08 > 0:49:11So what does the radar reveal?
0:49:17 > 0:49:19Well, the team found out
0:49:19 > 0:49:23that the dunes are not just piles of sand.
0:49:23 > 0:49:25They're far more complex.
0:49:26 > 0:49:30They're formed very slowly, over hundreds of years,
0:49:30 > 0:49:33and made up of many different layers.
0:49:33 > 0:49:35Some layers are denser, harder
0:49:35 > 0:49:37or more moist than others.
0:49:37 > 0:49:42And when sound waves from tumbling grains of sand on the surface
0:49:42 > 0:49:46hit one of these harder layers below, they bounce back up.
0:49:47 > 0:49:51So if you think about this layer of sand, underneath the dune,
0:49:51 > 0:49:53it behaves very much like a musical instrument
0:49:53 > 0:49:57that amplifies the sounds. Like, for example, a cello.
0:49:59 > 0:50:00The string is the initial tone,
0:50:00 > 0:50:05but the body of the cello actually amplifies and resonates the sounds.
0:50:05 > 0:50:09So why doesn't this happen in all sand dunes?
0:50:10 > 0:50:14Well, when it comes to booming dunes, size matters.
0:50:16 > 0:50:19The dune has to have a hard layer
0:50:19 > 0:50:22that's big enough to amplify the sound,
0:50:22 > 0:50:25and smaller dunes are too short to do this.
0:50:25 > 0:50:29And even the big dunes need the right conditions to sing.
0:50:29 > 0:50:32When they're wet, they won't make a sound.
0:50:33 > 0:50:36And then there's the sand itself.
0:50:36 > 0:50:40The grains must be well-rounded and roughly the same size.
0:50:41 > 0:50:43So, with all of these factors at play,
0:50:43 > 0:50:48you'd be very lucky to hear the song of a sand dune.
0:50:48 > 0:50:51But you don't have to travel to foreign climes
0:50:51 > 0:50:53to experience sandy sounds.
0:50:53 > 0:50:58At Porth Oer in Wales, you can walk on a squeaky beach!
0:50:58 > 0:51:00SAND SQUEAKS UNDER FEET
0:51:03 > 0:51:05The sand on the seashore here
0:51:05 > 0:51:08and on some other beaches around the world
0:51:08 > 0:51:11makes a high-pitched, squeaking sound.
0:51:12 > 0:51:14So what makes sand squeak?
0:51:15 > 0:51:19Well, it only happens on beaches where the sand is very pure,
0:51:19 > 0:51:21and made up of smooth grains of quartz.
0:51:29 > 0:51:32The sound may be made by friction,
0:51:32 > 0:51:34or by air escaping between the grains,
0:51:34 > 0:51:36as the sand is compressed.
0:51:38 > 0:51:43So sounds from the ground can be made by the ground itself.
0:51:46 > 0:51:51And new science has helped to solve an ancient desert mystery.
0:51:52 > 0:51:55So in the case of the singing sands,
0:51:55 > 0:51:59the explanation was very close at hand.
0:51:59 > 0:52:03But for our final story, we head to Buenos Aires in Argentina,
0:52:03 > 0:52:07where it seems that aliens have actually landed!
0:52:08 > 0:52:13This area has the most popular seaside resorts in the country.
0:52:13 > 0:52:16But at Monte Hermoso on April 3rd, 2007,
0:52:16 > 0:52:19it wasn't tourists crowding the beach.
0:52:22 > 0:52:27Hundreds of translucent orbs appeared on the beach overnight.
0:52:34 > 0:52:36They were firm to the touch,
0:52:36 > 0:52:39but filled with a thick, gelatinous liquid.
0:52:44 > 0:52:46And there was something moving inside.
0:52:50 > 0:52:54Witnesses wondered what on earth would hatch from this alien spawn.
0:53:00 > 0:53:03So what had created these eerie embryos
0:53:03 > 0:53:06and where had they come from?
0:53:06 > 0:53:10Their sudden appearance on the sand pointed to an invasion from the sea.
0:53:11 > 0:53:14But objects on the beach aren't always what they seem.
0:53:16 > 0:53:20Take this sand dollar, a type of sea urchin.
0:53:20 > 0:53:21Dried out on the beach,
0:53:21 > 0:53:24it looks like nothing that's come from the ocean.
0:53:24 > 0:53:28So working out the identity of these other-worldly orbs
0:53:28 > 0:53:30would need an expert eye.
0:53:30 > 0:53:34Fortunately, David Reid of the London Natural History Museum
0:53:34 > 0:53:36has seen something like this before.
0:53:36 > 0:53:39Well, these extraordinary, beautiful spheres
0:53:39 > 0:53:41that were washed up on the beach in Argentina
0:53:41 > 0:53:43might look alien to our eyes
0:53:43 > 0:53:47but in fact, they are the egg capsules of a marine snail.
0:53:48 > 0:53:53Hang on, a snail? Could a snail make something so extraordinary?
0:53:53 > 0:53:58Well, there's a lot more to these molluscs than meets the eye.
0:53:58 > 0:54:00Now, you'll all be familiar with this animal.
0:54:00 > 0:54:03This is the common British garden snail.
0:54:03 > 0:54:05You can find it all over the UK.
0:54:05 > 0:54:10But molluscs like this come in a great range of shapes and sizes.
0:54:10 > 0:54:14The largest on land is this, the African land snail,
0:54:14 > 0:54:19and they can grow to up to 40 centimetres in length
0:54:19 > 0:54:21and weigh up to 900 grams.
0:54:23 > 0:54:27And in the ocean, the world of snails gets even stranger.
0:54:30 > 0:54:35There are as many as 18,000 different species of marine snail.
0:54:35 > 0:54:39Far from wandering the sea bed at a snail's pace,
0:54:39 > 0:54:42they can have incredible adaptations.
0:54:42 > 0:54:48This plough snail uses its large foot to surf up the beach,
0:54:48 > 0:54:51where it feeds on dead animals washed up by the tide.
0:55:01 > 0:55:03Other marine snails have come up
0:55:03 > 0:55:05with some pretty radical ways to reproduce.
0:55:07 > 0:55:11And one of them makes those orbs from Argentina.
0:55:12 > 0:55:14This is quite a large marine snail,
0:55:14 > 0:55:16it's one of the largest in the region,
0:55:16 > 0:55:18and this is a specimen of that snail.
0:55:18 > 0:55:20It's called Adelomelon brasiliana
0:55:20 > 0:55:22and it occurs from South Brazil,
0:55:22 > 0:55:25through Uruguay to northern Argentina.
0:55:26 > 0:55:31So why does this snail produce such big and bizarre-looking egg cases?
0:55:31 > 0:55:35Well, it lives in shallow waters, just off shore,
0:55:35 > 0:55:39where the sandy sea bed presents a bit of a challenge.
0:55:39 > 0:55:42Most of them are attached to a small pebble
0:55:42 > 0:55:45or a sea shell on the sea floor or perhaps to a rock.
0:55:45 > 0:55:48These ones are unusual in that they're not attached to anything,
0:55:48 > 0:55:51perhaps simply because the animals are living on soft sand.
0:55:51 > 0:55:55There aren't any hard objects there for them to lay their eggs on.
0:55:56 > 0:55:58With nothing to attach their eggs to,
0:55:58 > 0:56:02the snails literally put all their eggs in one rolling basket,
0:56:02 > 0:56:05and leave them to float along the bottom.
0:56:07 > 0:56:11So, the orb isn't an egg, it's a nest!
0:56:11 > 0:56:14It contains all the nutrients the embryos need to grow
0:56:14 > 0:56:19and the flexible outer membrane keeps the tiny snails protected
0:56:19 > 0:56:21until they're ready to hatch.
0:56:21 > 0:56:24But these free-floating orbs are vulnerable.
0:56:35 > 0:56:38Storms in shallow seas can churn up the sea bed.
0:56:40 > 0:56:42And local residents in Argentina
0:56:42 > 0:56:45have confirmed that there was a big storm
0:56:45 > 0:56:50the night before these alien orbs appeared on the beach.
0:56:50 > 0:56:54So for the snails, it was a case of terrible timing.
0:56:54 > 0:56:58Sadly, this mass stranding will have had an impact
0:56:58 > 0:57:01on the local snail populations for that year.
0:57:01 > 0:57:06But even scientists rarely get to see these extraordinary eggs.
0:57:06 > 0:57:09So even if it initially looked a little out of this world,
0:57:09 > 0:57:11this was an opportunity to see
0:57:11 > 0:57:14something usually hidden beneath the waves.
0:57:17 > 0:57:21These stories show that apparently alien encounters
0:57:21 > 0:57:23are often more bizarre than they seem.
0:57:29 > 0:57:32Whether it's noises from the sky, sonorous sand dunes,
0:57:32 > 0:57:35or snails invading the beaches of South America,
0:57:36 > 0:57:40it just goes to show that sometimes in science fiction
0:57:40 > 0:57:43the science is far stranger than the fiction.
0:57:45 > 0:57:48When we encounter something bizarre,
0:57:48 > 0:57:50it's human nature to seek an explanation,
0:57:50 > 0:57:54and this quest for knowledge has led to the discovery
0:57:54 > 0:57:58of many of the world's most fascinating natural secrets.
0:57:58 > 0:57:59But that said,
0:57:59 > 0:58:04whilst many of these bizarre phenomena have been explained,
0:58:04 > 0:58:08others remain an enigma. And there is one thing for certain -
0:58:08 > 0:58:13there's a lot more weirdness out there just waiting to be discovered.
0:58:15 > 0:58:18Next time on Nature's Weirdest Events,
0:58:18 > 0:58:22we meet a bear going that extra mile for a meal.
0:58:22 > 0:58:25Goats that keel over at the first sign of trouble.
0:58:28 > 0:58:31And a lobster with a split personality.