Episode 2 Nature's Weirdest Events

However well we think we know our planet, the natural world still has

the ability to surprise us, to shock us, sometimes even to scare us

with its extraordinary events and bizarre behaviours.

And given modern technology, nature's weirdest phenomena

are now frequently caught on camera, wherever and whenever they occur.

So this means that we can now bring you the strangest

stories our world has to offer.

From fish walking out of the water...

Oh, my gosh! That is blowing my mind!

..to alien spawn on the sands of South America...

..and a monster from the ocean depths.

When I touched it, it just sort of

felt like a soft, jelly-like substance.

With the help of eyewitnesses, experts and scientists,

we're going to try and explain what on earth is going on.

Nature can astound and confound us and sometimes events can be so

bizarre that they even challenge the way that we think about our world.

These incidents can be so extraordinary,

they even appear to be somewhat supernatural.

We start with events so unsettling

they could be seen as omens foretelling the end of days.

From trees that bleed...

..to bees making horrifying honey.

But our first portentous event is in Florida,

where truly strange behaviour is alarming the locals.

-What in the world?

-How weird is that, huh?

-It is weird.

-Hopping around in the yards...

My God, where are they coming from?

Quiet suburban gardens and homes are being overrun.

-I don't know, that's weird, huh?

-We don't know, it's so weird.

-What are they?

-It's fish!

-Fish.

Fish, walking the land. This seems like a very bad sign.

Look at that one.

-There's one over there.

-Where?

-Over there!

-There's tons of them.

-I know, what the...?

They're not just invading this neighbourhood.

This is happening all over Florida.

After a storm, these bizarre fish appear as if from nowhere,

and every year, their numbers are increasing

to plague proportions.

Crawled out through the grass and came out here?

-Something like that.

-There's another one down there.

-Help.

-It's weird.

-Oh, my gosh!

-It's just amazing.

That is blowing my mind!

So what on earth are these freaky fish?

And why have they taken to the streets?

Feelers which look like whiskers give them away -

this is a type of catfish.

But how is this aquatic animal staying alive in air?

Most fish die if they're out of water for more than a few minutes.

Their gills can't extract oxygen from the air

and the fish suffocates.

But these catfish have a clever adaptation to help them

breathe out of water, as ecologist and

fish expert Bill Loftus explains.

It does this by use of a specialised organ that

lies behind the gill chamber

inside of its head, and it can take oxygen from the air through

that organ and put it into its bloodstream.

And that's an amazing adaptation for this animal to

allow it to get out on land and to move around.

And these fish don't just have the ability to breathe air.

Oh, no, they've taken life on land one step further.

They're called walking catfish.

These piscatorial pedestrians don't just

flap around wildly like a fish out of water.

They move with a determined purpose.

Most fish are only adapted for swimming,

so how are they walking on land?

It's all down to the evolution of these front or pectoral fins here,

which have a rigid spine

running through them. And this means that they can

support the front of the fish's body weight and

when they pivot from side to side

and thrash vigorously with their tail,

they move forward.

It's a bit like us doing a commando crawl, using our elbows,

pushing with our feet.

Now, it might sound and look a bit clumsy,

but it's actually very efficient and it makes these

things very difficult to stop.

So why would a fish need to breathe air and walk on land?

Well, they're not the only fish that leave water.

A few other species come onto land if the water

quality deteriorates, or to escape aquatic predators.

But walking catfish have another, more sinister purpose.

These fish are on a mission.

They're hungry and they're out hunting.

As Florida resident

and tropical fish breeder Colin Calway discovered to his horror.

When you're looking at a pond every day, you know the type of fish you

got in there, and there's a strange activity, something's not right,

and you've got to find out what it is.

So we pumped the pond down

and instead of approximately 10,000 rosy barbs,

we had - it looked like - 10,000 walking catfish in their place.

A staggering 10,000 prize specimens became fish food

almost overnight.

But that was just the start of the problem.

These voracious predators eat everything in their path

and they'll walk a long way to find their prey.

When they've eaten everything they can in the pond,

almost wiped it out, they'll wait for that night when a good

thunderstorm comes or rain comes or very, very heavy dew.

And then they'll leave the pond in large numbers and they'll

keep moving up the ditches and through the grass until they find

another pond.

Clear that one and they move on again.

And that pretty well wiped us out as tropical fish farmers.

But it's not just fish farms.

Florida's native species are also under attack.

And the local wildlife isn't adapted to cope.

You see, walking catfish aren't native to Florida.

They originally came from Southeast Asia as exotic pets,

but in the 1960s, a few were released from aquariums

and now they spread across most of the state.

For anything in their path, this is a catfish catastrophe.

Walking catfish are very broad feeders,

so they will feed on fish, invertebrates, amphibians and

pretty much the whole gamut of aquatic insects.

And the devastation on our small native fishes

and invertebrates is...is just tremendous.

Walking catfish cause so much destruction, they've actually

made the list of the top 100 world's worst invaders.

They've got an arsenal of adaptations for overground invasion.

They can walk the land, breathe air

and they're also covered in slime, so they don't dry out.

And they can survive several months without food.

So whilst the disturbing sight of

walking fish isn't a sign of the apocalypse,

it does spell disaster for local wildlife.

It's a terrifying takeover, one small step at a time.

And now, from apocalypse to apocryphal tale. We're going to

witness an event so alarming,

it's easy to see why people might think that the

end of the world is nigh.

Trees. They've inspired myths and folklore.

They can be haunting, even eerie.

Some people even believe that trees have a soul.

But could they also have a heart and bleed?

Well, in this incredible event from Australia,

it certainly looks like it.

Chris Wharton was chopping down a tree

when he got the shock of his life.

Here we have blood pumping out of a tree after I cut it.

I do not understand why this tree has - apparently -

blood pumping out of it,

but the tree itself is still pumping.

Strangest thing I've ever seen while playing with me chain saw.

But this isn't an isolated incident.

All around the world, people are being

alarmed by blood pouring from trees.

Look! Look! The tree is bleeding! Look!

-Looks like blood, though, don't it?

-Uh-huh!

-It does look like blood.

-A bleeding tree.

I got to send this to Steve.

David Rose is a tree pathologist.

He's heard reports of these incidents.

We get quite a few every year, varying from ones where

people have cut the branch off the tree and it's started to bleed,

through to ones where the bleeding is coming through what appears to be

perfectly intact bark.

And the ones that have got bleeding through the bark, they worry

about is it a nasty disease, or is it something much more supernatural?

We had a case in a churchyard in Pembrokeshire where the

vicar contacted us and he had been driven to distraction by

numbers of people coming in to see

this miracle bleeding yew in his churchyard.

He had people who'd come to see the miracle.

Yews are amongst our most ancient trees,

they can live for thousands of years.

Some revere them as sacred, but morbid myths also surround them.

Yews are common in churchyards, standing sentinel

over graves, and they're regularly reported to be bleeding.

So could the red fluid oozing from these trees really be blood?

Just like animals, trees have circulation.

Inside of the body of the tree here

are many millions of tiny, microscopic vessels which carry

food and minerals around the tree to help it live and grow.

Now, there are two basic types. The first, xylem.

This draws water up from the roots, through the trunk of the tree

all the way to the top, but importantly, into all of the leaves,

where it's needed for photosynthesis -

the process by which the tree produces its food.

Once it's made that food, a second set of vessels,

the phloem, transports the food from the leaves to other parts of

the tree and even all the way down to the roots,

where it can be stored.

So if we cut across the trunk,

that would be a bit like cutting across the limb of an animal.

You would sever the artery and the fluid would gush out.

The most extreme bleeding events happen in spring,

when this fluid, called sap, is rising rapidly in the tree.

The sap is at high pressure until the leaves

open and begin to evaporate the water.

Any injury releases this pressure.

This apparent bleeding can look distressing,

but the sap could be the tree's way of trying to heal.

If you have a disease then it's much thicker

and often dries to a thick, blackish crust,

and it contains a lot of antiseptic compounds designed to seal the wound.

So the sap effectively forms a scab.

The healing agents in it can cause the red colour.

Sometimes the sap will also change colour to red

when it's exposed to the air.

So that's why it can look like blood.

Sadly, for some injuries, no amount of healing sap is going to help.

Tree blood, flowing like a river.

We cut through an artery there, buddy.

I don't think he's going to be coming back after this.

-Try to plug me fingers in.

-Go on. Oh, dear.

Scarlet sap is shocking enough,

but when something familiar turns a weird colour,

it can seem like the world has been turned on its head.

For our next story, we head to the village of Ribeauville, in France.

The village is set in the beautiful Alsace region.

Famed for its wine, it also produces a very distinctive type of honey.

It's famous for its unique flavour, the result of the bees foraging in

fir trees in the nearby mountains.

But in 2012, the local beekeepers had a shock.

When they opened their hives, they found something truly disturbing.

The bees were making vivid green honey.

In other hives, it was bright blue.

In fact to the beekeepers' horror, they found several unusual colours.

This was unheard of. Some people even wondered if something had

tipped the very balance of nature.

And there is cause for concern. You see, bees

are responsible for pollinating most of our crops.

If something happened to the bees,

this could have a catastrophic impact on the whole food chain.

So this Technicolor turn of events is truly alarming.

But why would bees make multicoloured honey?

Well, this isn't the first case of surprising shades of honey.

It's also happened in a place you might not expect to find a beehive.

In New York City, beekeeping is an increasingly popular pastime.

Andrew Cote is head of the New York Beekeepers Association

and he's been keeping bees since he was a boy.

Good morning. Honey for you, Miss? No?

-Too sweet?

-Sweet enough?

Since I've been keeping bees in New York City, I've come across

bright red, green and blue honey.

In the city that never sleeps,

busy bees also make strange honey, although only one colour at a time.

So is there something about the urban environment that explains it?

In New York, bees forage for nectar from flowers in parks and gardens.

Nectar is mostly sugar water and it's the key ingredient of honey.

The bees take it back to their hive,

where worker bees pass it around, chewing it.

They then place it in a cell of their

honeycomb and buzz their wings

to evaporate the moisture and the result is honey.

Different flowers produce slightly different nectar

and this affects the honey colour,

normally from pale gold to dark brown.

But never normally these bright colours.

In the urban jungle, it's easy to get a sugar fix.

In our takeaway, fast food world, sugary snacks are everywhere.

And it's not just us who crave sweet treats.

Driven by their desire for sugar, the bees are homing in too.

A friend of mine found that her honey was bright red

and another fella, he found that his honey was bright red.

And it turned out that in this little peninsula area of Brooklyn

called Red Hook, there is a maraschino

cherry factory that's been there since the 1940s and the bees

were sipping up the run-off from

that factory, and when there's

a concentrated, sugary syrup that's just ready to be picked up,

it's very hard for the bee to resist.

Like it would be hard for a child to resist snack food, junk food.

There are accounts of it happening in England,

bees going near a Coca-Cola bottling plant and producing

some kind of sickly, sweet nectar.

So what about Andrew's green honey?

I really don't know what produced that green honey,

I think it was probably antifreeze.

Whilst it's toxic to us, antifreeze is incredibly sweet,

and bees are attracted to the scent.

So in their relentless hunt for sugar,

these industrious insects are making

a bee-line for anything sweet,

and what they find can be very brightly coloured indeed.

And once one bee from a colony finds it, they all will.

When they return from their foraging trips, bees perform

a "waggle dance", which gives others the exact

direction and distance to the food source.

So, before long, the whole hive is filled with strange-coloured honey.

But should we eat it?

It depends on how experimental the person is.

I don't think it's necessarily a good idea to try an odd-coloured

honey, or drink a plutonium milkshake, or do anything risky.

It can't be sold as food, only as a curiosity item.

I think it happens especially in New York

because we're living in such close proximity to

one another, even our bees are right in our midst.

Brightly coloured honey might be disturbing to us but for urban bees,

using whatever sugar they can find makes perfect sense.

So this funny honey isn't a sign of the end of days,

it's a sign of our changing times.

But what about those French bees, living out in the countryside?

How did they create honey in such a range of bright colours?

Well, it turned out that they were flying

a couple of miles across the fields to a waste reprocessing plant,

where they were feeding on the discarded husks of M&M's.

So it turns out

that it was a pot of man-made sugar that was providing

all the colours of the rainbow.

What these stories reveal is that events we might read as signs

of the apocalypse may actually be nature's survival strategies.

Whether it's a fish taking over new territory,

healing sap pouring from trees,

or streetwise bees on a sugar rush.

Far from signalling the end of the world, we are seeing nature

working in a perfect but rather peculiar way.

Next, it's time to meet animals which have formed unexpected

and bizarre bonds.

Like the cat rearing a remarkable litter.

Or a sea creature that's more than the sum of its parts.

But first, we travel to the Azores, islands in the Atlantic Ocean.

In September 2011, marine biologists took to the

high seas in search of whales.

On a typical day, we would go out into the open water

and we would look for plumes of misty vapour.

From the surface, you can only get a little

bit of a glimpse of what's happening beneath the surface.

It's kind of like an iceberg, you know?

80% of the action is actually below the surface.

Dr Alexander Wilson

is a research associate from Carlton University in Canada.

And what he experienced that day came completely out of the blue.

He was filming this pod of sperm whales,

the world's largest predators.

They come to these waters to rear their calves.

But there was something very surprising about this family.

A bottlenose dolphin was swimming with them.

The dolphin was a very unique animal.

He was a full-grown adult male in very good condition

from what we could tell.

But he obviously had this very visible spinal malformation.

Despite its birth defect,

the dolphin was keeping pace with the whales and remarkably,

it seemed to be deliberately interacting with them.

The dolphin tended to use its tail flukes, its flippers

and dorsal fin, as well as nuzzling with the sperm whales.

And the whales were responding.

They would roll around

and rub their sides along the body of the dolphin and this is

a type of behaviour that they also demonstrated to each other.

Close interaction between dolphins and sperm whales

is almost unheard of, and this is the first time it's been filmed.

So, why would two such different species keep such close company?

Well, there are a few other examples

where different species club together.

In India, chital deer often graze alongside

langur monkeys, so there are more eyes looking out for danger.

The deer even recognise the monkey's alarm calls,

helping them to make a quick getaway.

So is this why the dolphin decided to swim with the sperm whales?

Did these massive marine mammals provide protection?

Given that there's not very many predators that are capable of

feeding on such a large dolphin in the area,

this is unlikely to be a sole explanation.

But we did see them interacting in a very friendly way,

making a lot of physical contact, and so it seems to

suggest that some kind of underlying social factor is involved.

And this would make sense for our dolphin.

Dolphins are exceptionally sociable animals.

They usually live in groups of up to 100.

Sometimes, their pods will even merge for a while,

forming spectacular schools up to 6,000 strong.

Dolphins often work together to catch food

and social interaction is an important part of their daily lives.

So why was our dolphin all on his own?

It's highly probable

that the fact that this dolphin did have a very unique

spinal malformation was part of the reason for this type of interaction.

In dolphin groups, they exhibit a very strong hierarchy

and this dolphin - for some reason -

might have been lower on the totem pole than other members.

And could have been picked on by group members.

So this dolphin may have been deserted by its own pod.

Like us, dolphins find isolation very stressful.

Lonely dolphins may even seek out other species for company.

And they don't even have to be marine animals.

A few years ago in Ireland,

a dolphin forged a friendship with a local dog.

The dog and the dolphin would meet almost every day

in Tory Island Harbour and they spent many hours together.

So if our dolphin had been abandoned, maybe

he sought out the sperm whales.

But there's more beneath the surface of this story.

You see, it's the first time that anyone has ever seen sperm whales

interacting with another species like this.

Sperm whales aren't known to associate with any other species,

it's never been seen before.

This is so unusual, we can only speculate on why they're doing it.

Perhaps the whales mistook the dolphin for one of their own.

Sperm whale calves are about four metres long at birth,

about the same size as this dolphin,

and the whales were touching the dolphin

in the way that they would touch their calves.

But there's another intriguing possibility.

For centuries, humans have believed that whales can display emotion.

Indeed, they've been revered as spirit animals in many cultures.

But now recent research has shown

that they can display empathy, a care for others.

Examinations of the brains of certain species of whale and dolphin

have shown that they have the types of neurons

typically associated with social organisation,

speech and recognising suffering in other animals.

So it seems that science is finally catching up

with ancient-held beliefs that we're not the only ones out there

that care for other animals.

So it might just be that the whales were caring for the dolphin

and for his part, the dolphin was seeking out their company.

Whatever was going on here,

there's no doubt that this was a truly unique encounter.

These two marine mammals forged an unlikely bond,

but some animals create even freakier extended families.

Nothing could be stronger than the connection

between a mother and her young.

Big cats are devoted parents,

and their domestic cousins are no less attentive.

But in some feline families, the laws of nature

seem to get turned on their head.

This is Sonya, a cat from central Russia,

who's taken motherhood to the extreme.

These three baby hedgehogs were orphaned

and wouldn't have survived on their own.

But incredibly, Sonya adopted them

and suckled them as if they were her own kittens.

But remarkably, cats have adopted other small mammals,

like rabbits and squirrels.

And take the case of the cat in Ireland

that adopted three tiny ducklings.

She was rearing them with her own kittens.

Birds normally feature high on a cat's menu,

so to see this cat being so gentle with these baby birds is remarkable.

So why are these cats suppressing their natural hunting instincts

to look after other species?

Well, in the wild,

lionesses sometimes care for cubs that aren't their own.

Forming a cub creche helps them share the workload of hunting

and suckling the cubs.

So cats can have a flexible approach to childcare.

But why would they adopt an animal

from a completely different species?

Most mammals give birth to small, vulnerable babies,

completely dependent on their mother.

A strong bond between them is vital.

When a mammal gives birth and then suckles her young,

she's affected by a powerful hormone called oxytocin

and this promotes feelings of love and bonding.

Whenever domestic cats adopt other species,

it turns out they've recently had their own kittens.

A slave to their hormones,

they're primed to care for young animals, any young animals.

Just a few days later, and they wouldn't have taken them in.

In fact, they might have eaten them.

So this explains why cats might adopt another species,

but what about those ducklings?

Surely they should have been afraid of a potential predator like a cat?

Well, for them, there was another powerful instinct at work.

In the 1930s, an Austrian scientist, Konrad Lorenz,

discovered a strange phenomenon.

Lorenz worked with young goslings and found that,

if he was the first thing they saw after hatching,

they would follow him like a parent.

They had "imprinted" on him.

So this could explain how our ducklings bonded to the cat.

But why does imprinting happen in the first place?

Well, birds that nest on the ground are vulnerable to predators,

so their chicks have to be on the move

as soon as they've hatched.

It's vital that they follow their parents

and don't wander off into danger,

and that's where imprinting comes in.

There you go.

So imprinting is an amazing survival mechanism

whereby sensory information is "stamped"

into the brain of tiny, vulnerable and mobile young,

like these ducklings.

Then they're best placed to recognise those

who are responsible for feeding them and protecting them.

But imprinting is quite unbiased.

Movement, smell and sound are important,

but if I'm honest with you,

the imprinted object doesn't even need to be alive

and in the past, young animals like these ducklings

have imprinted upon watering cans, robots,

even plastic milk bottles tied to the back of electric toy trains.

So when a duckling imprints upon a human, or a cat,

it's nothing personal.

They might have even imprinted on a pair of wellingtons.

So in the strange case of the cat and the ducklings,

it was all down to timing.

The cat was flooded with hormones which made her bond with the ducks,

whilst the ducks, being so young, imprinted on her.

After a few weeks, they went their separate ways.

That's the reason behind

the most unorthodox foster families on the planet.

It's strange to see a bond between natural born enemies.

But some close relationships are even weirder.

Next, we travel to Tasmania,

where divers discovered something very unusual.

We went off down with another couple of guys on the boat

to jump in and film some seals.

What Mick Baron saw next took him completely by surprise.

Well, I jumped in the water first

and then my camera was passed down to me and while I was setting it up,

I saw this strange animal about 30 metres away.

I thought, "Wow! What's this?" So I yelled out

to the other two guys on the boat, "Come on, guys. Get in here,

"you've got something here you'll never see again in your life."

An enormous, tube-shaped structure was hanging in the water.

It was about ten metres long.

When I touched it, it didn't actually react,

it just sort of felt like a soft, jelly-like substance.

And strangest of all, the tube was glowing with an eerie blue light.

Was its origin even alien?

I've been diving for quite a long time, say, 40 years,

and when I saw this one, I thought,

"Wow! This is a pretty unusual experience."

So what was this gigantic, glowing tube? And was it even alive?

When it comes to the ocean, we've barely scratched the surface.

It's often said that the deep sea

is Earth's last unexplored frontier.

Teeming with alien-looking life.

But even these bizarre creatures have features we can recognise.

Eyes.

Limbs.

Teeth.

The thing the divers encountered had none of these.

But there is another possibility.

You see, some marine animals live together,

forming a much bigger organism.

Take coral reefs.

Corals are formed by colonies of creatures known as polyps.

These tiny animals build a hard exoskeleton around them.

And living together in their billions,

they form some of the world's largest

and most spectacular structures.

Like the Great Barrier Reef.

And it's not just corals that take to communal living.

Our giant tube is actually a colony of tiny animals,

known as a pyrosome.

Rebecca Helm is a research graduate at Brown University.

She's been studying these strange creatures.

Pyrosomes are made up of tens to thousands of clones

of very small-bodied animals,

and these clones all stick together to each other

with shared tissues and form this large, tube-shaped colony of animals.

Pyrosomes are usually clear.

They can be kind of a reddish pink, even,

and they can most of the time get to a couple of centimetres,

but the largest ones can get up to 20 metres.

This particular pyrosome was one of the largest ever caught on camera.

Together, these tiny creatures cruise the oceans

as one colossal structure.

They prefer warm waters close to the surface

and the tubular shape helps the animals move.

You see, each individual takes in water

which it squirts into the hollow centre,

moving the whole colony by jet propulsion.

Although the tube has a man-sized opening at one end,

they aren't dangerous to us.

Pyrosomes are filter-feeders,

which feast on micro-organisms like plankton and bacteria.

Sometimes animals do find their way inside by accident,

like this shrimp.

But what about that eerie glowing?

Well, the Greek word "pyro" means "fire".

And this is bioluminescence.

It acts as a warning sign that a predator might be about.

Pyrosomes are incredibly bioluminescent.

Bioluminescence is the ability of an organism to produce light

using a mixture of chemicals

that they keep in separate compartments in their body,

and then when the time is right, kind of like a glowstick,

they mix them all together, and that creates a luminescence.

80-90% of deep-sea creatures are bioluminescent.

They usually glow green or blue, colours that travel well in water.

And pyrosomes are some of the brightest animals in the ocean.

These communities truly are wonders of nature.

A "superorganism" of tiny animals working as one.

A pyrosome really is greater than the sum of its parts.

In these extraordinary stories, we've seen what happens

when animals forge relationships

beyond the normal boundaries of biology,

whether it's a lonely dolphin finding new friends,

cats adopting animals that should be dinner...

or a colony of tiny creatures which live and glow together.

When some animals get together, the results can be truly bizarre.

Finally, we investigate stories so strange,

many think there's an extra-terrestrial explanation.

From the mystery of the droning sand dunes...

Wow.

..to alien spawn on our beaches.

But for our first "alien invasion", we head to Central Canada.

The city of North Battleford. Population, 14,000,

and usually a pretty peaceful place to live.

But in January 2012, as night fell, things got very strange indeed,

as the town was terrorised by earth-shattering noises,

and they were coming from the sky.

EERIE HORN-LIKE SOUND

NOISE CONTINUES

LOUD, DISCORDANT NOISE

Me and Tommy are hearing noises. Trumpets.

This town is having strange things going on.

Yep.

LOUD TRUMPETING CONTINUES

After a sleepless night straight from a sci-fi movie,

the residents of North Battleford were worried.

People were kind of mildly talking about it,

but no-one really wanting to sound like they were crazy!

People were phoning in, they were phoning in to the police,

they were phoning in to various agencies asking what was going on.

So it frightened people.

It was very disturbing. It was really chilling to hear

and to know that everybody else was hearing it as well.

It kind of sounded like there was a transformer right outside my window.

Literally sounded like trumpets playing from the sky.

With no obvious explanation for these alien acoustics,

the rumours ran wild.

We heard all kinds of things, electromagnetic waves.

Echoes, because of ice moving in the Arctic.

Alien invasions.

Cars sliding on the train tracks.

Maybe snow clearing.

But this story gets stranger, because as it turns out,

events just like this are happening all around the world.

Was it an elaborate prank, the sound of aliens, or something else?

Reports of extra-terrestrial sounds from the sky

are hitting the headlines across the planet.

METALLIC WHINING

LOUD METALLIC WHINING

In some places, the noises are so loud, they set off car alarms.

CAR ALARM BLARES IN DISTANCE

So is this the start of a close encounter?

What were the unnerving noises heard in North Battleford?

Trevor Cox is a professor of acoustics at Salford University.

There's lots of examples of unexplained sounds,

which usually, in the end, you can find some cause for.

I mean, little earthquakes can cause low frequency sounds

that people can hear,

or you might have the distant sounds of things like thunder.

It's unlikely that this would directly explain

the sounds in North Battleford,

as no earthquakes or storms were recorded that day.

But could the weather be a clue?

There is a connection between many of the events.

They happened in winter,

and it turns out that temperature has a strange effect on sound.

Now, we all know that hot air rises,

but I can demonstrate that property using this coloured water.

I've got warm yellow water in the bottom bottle here,

and cold blue water in the one at the top,

and just look at what happens

if I pull this piece of plastic which is keeping them apart away.

Immediately, we get mixing.

On occasions, though, when the ground is so cold,

a layer of cold air is trapped beneath a layer of warm air.

So again, cool blue water here and the yellow warm water at the top,

and this time, if I remove the plastic really carefully,

you can see that there is no mixing.

Now, what's interesting is that when sound is moving through air,

it moves more rapidly through warm air

than it does through cool air.

Sound waves normally travel up in straight lines

and disappear into the atmosphere, but in this case

they hit that barrier of warm air

and then are bent back down to the earth,

and this means they can travel great distances from the point of origin.

So although the alarming sounds in North Battleford

appeared to have come from the sky,

the source was probably on the ground, hundreds of miles away.

But that doesn't explain why many of the noises were so otherworldly.

Grating, droning, trumpeting -

it's the soundtrack to an alien insurrection.

So what explains the extra-terrestrial acoustics?

By the time you've heard these sounds,

they will have travelled a long distance

and the high frequencies will have been lost,

just by absorption in the air, so all they're hearing is the low frequency.

So they're going to sound a bit odd. It's a bit like

you've taken a recording and put it through a graphic equalizer

and you've only got the bass left.

So this explains why these noises sound so alien

and this could happen anywhere, if the conditions are right.

Really loud sound waves can travel huge distances

and the best example in the UK

is probably the Buncefield oil depot which blew up a few years back,

and that sound travelled all the way to Holland.

It was actually heard 200 miles away.

So the sound waves which normally would be going upwards

were bent down and were heard all the way over in Belgium and Holland.

If I was going to guess, the most likely cause of the noise in Canada

was probably some industrial machinery,

rather than being some sort of weird UFO effect.

We may never know what actually made

the strange noises in North Battleford

because the source was so far away.

But it was likely to have been man-made and mechanical.

So although more disturbed nights might lie ahead,

the residents of North Battleford now know the aliens aren't invading.

At least, not yet.

So physics can account for nerve-racking noises from the sky.

But what about strange sounds

coming from beneath the surface of the earth?

For centuries, travellers have told tales of eerie sounds in the desert.

But these are foreboding and extreme landscapes...

..where your mind can play tricks.

And until recently, these tales were only whispers on the wind.

Today, deserts are far more accessible

and now people have started recording these strange sounds.

LOUD DRONING

Wow!

They're hearing deep, droning noises in the dunes.

We're in Doha, Qatar. The ground is shaking.

It's vibrating!

In the Gobi desert in China, to the Namib in Africa

and deserts in North America, people are hearing unearthly sounds.

The sound is very, very loud,

I would say standing next to a bass in a rock concert, it's dead loud.

And it seems to be coming from the desert itself.

When you're sliding down the dune, your whole body starts to vibrate

and you are really wondering where the sound is coming from,

but it's from underneath you.

Something inside the dune is making earth-shaking sounds.

So what's hiding inside these dunes, and creating this deafening drone?

Some of these dunes are vast.

Something large could easily be hidden inside.

For more than 100 years,

scientists have been trying to find the source of these sounds.

And finally, after decades of speculation,

one team might have unearthed the secret of the dunes.

Dr Nathalie Vriend is part of a team working in the California deserts.

When we're doing our research,

we're measuring the sound frequency with a microphone.

And we're also measuring

the internal structure of the dune with radar.

So what does the radar reveal?

Well, the team found out

that the dunes are not just piles of sand.

They're far more complex.

They're formed very slowly, over hundreds of years,

and made up of many different layers.

Some layers are denser, harder

or more moist than others.

And when sound waves from tumbling grains of sand on the surface

hit one of these harder layers below, they bounce back up.

So if you think about this layer of sand, underneath the dune,

it behaves very much like a musical instrument

that amplifies the sounds. Like, for example, a cello.

The string is the initial tone,

but the body of the cello actually amplifies and resonates the sounds.

So why doesn't this happen in all sand dunes?

Well, when it comes to booming dunes, size matters.

The dune has to have a hard layer

that's big enough to amplify the sound,

and smaller dunes are too short to do this.

And even the big dunes need the right conditions to sing.

When they're wet, they won't make a sound.

And then there's the sand itself.

The grains must be well-rounded and roughly the same size.

So, with all of these factors at play,

you'd be very lucky to hear the song of a sand dune.

But you don't have to travel to foreign climes

to experience sandy sounds.

At Porth Oer in Wales, you can walk on a squeaky beach!

SAND SQUEAKS UNDER FEET

The sand on the seashore here

and on some other beaches around the world

makes a high-pitched, squeaking sound.

So what makes sand squeak?

Well, it only happens on beaches where the sand is very pure,

and made up of smooth grains of quartz.

The sound may be made by friction,

or by air escaping between the grains,

as the sand is compressed.

So sounds from the ground can be made by the ground itself.

And new science has helped to solve an ancient desert mystery.

So in the case of the singing sands,

the explanation was very close at hand.

But for our final story, we head to Buenos Aires in Argentina,

where it seems that aliens have actually landed!

This area has the most popular seaside resorts in the country.

But at Monte Hermoso on April 3rd, 2007,

it wasn't tourists crowding the beach.

Hundreds of translucent orbs appeared on the beach overnight.

They were firm to the touch,

but filled with a thick, gelatinous liquid.

And there was something moving inside.

Witnesses wondered what on earth would hatch from this alien spawn.

So what had created these eerie embryos

and where had they come from?

Their sudden appearance on the sand pointed to an invasion from the sea.

But objects on the beach aren't always what they seem.

Take this sand dollar, a type of sea urchin.

Dried out on the beach,

it looks like nothing that's come from the ocean.

So working out the identity of these other-worldly orbs

would need an expert eye.

Fortunately, David Reid of the London Natural History Museum

has seen something like this before.

Well, these extraordinary, beautiful spheres

that were washed up on the beach in Argentina

might look alien to our eyes

but in fact, they are the egg capsules of a marine snail.

Hang on, a snail? Could a snail make something so extraordinary?

Well, there's a lot more to these molluscs than meets the eye.

Now, you'll all be familiar with this animal.

This is the common British garden snail.

You can find it all over the UK.

But molluscs like this come in a great range of shapes and sizes.

The largest on land is this, the African land snail,

and they can grow to up to 40 centimetres in length

and weigh up to 900 grams.

And in the ocean, the world of snails gets even stranger.

There are as many as 18,000 different species of marine snail.

Far from wandering the sea bed at a snail's pace,

they can have incredible adaptations.

This plough snail uses its large foot to surf up the beach,

where it feeds on dead animals washed up by the tide.

Other marine snails have come up

with some pretty radical ways to reproduce.

And one of them makes those orbs from Argentina.

This is quite a large marine snail,

it's one of the largest in the region,

and this is a specimen of that snail.

It's called Adelomelon brasiliana

and it occurs from South Brazil,

through Uruguay to northern Argentina.

So why does this snail produce such big and bizarre-looking egg cases?

Well, it lives in shallow waters, just off shore,

where the sandy sea bed presents a bit of a challenge.

Most of them are attached to a small pebble

or a sea shell on the sea floor or perhaps to a rock.

These ones are unusual in that they're not attached to anything,

perhaps simply because the animals are living on soft sand.

There aren't any hard objects there for them to lay their eggs on.

With nothing to attach their eggs to,

the snails literally put all their eggs in one rolling basket,

and leave them to float along the bottom.

So, the orb isn't an egg, it's a nest!

It contains all the nutrients the embryos need to grow

and the flexible outer membrane keeps the tiny snails protected

until they're ready to hatch.

But these free-floating orbs are vulnerable.

Storms in shallow seas can churn up the sea bed.

And local residents in Argentina

have confirmed that there was a big storm

the night before these alien orbs appeared on the beach.

So for the snails, it was a case of terrible timing.

Sadly, this mass stranding will have had an impact

on the local snail populations for that year.

But even scientists rarely get to see these extraordinary eggs.

So even if it initially looked a little out of this world,

this was an opportunity to see

something usually hidden beneath the waves.

These stories show that apparently alien encounters

are often more bizarre than they seem.

Whether it's noises from the sky, sonorous sand dunes,

or snails invading the beaches of South America,

it just goes to show that sometimes in science fiction

the science is far stranger than the fiction.

When we encounter something bizarre,

it's human nature to seek an explanation,

and this quest for knowledge has led to the discovery

of many of the world's most fascinating natural secrets.

But that said,

whilst many of these bizarre phenomena have been explained,

others remain an enigma. And there is one thing for certain -

there's a lot more weirdness out there just waiting to be discovered.

Next time on Nature's Weirdest Events,

we meet a bear going that extra mile for a meal.

Goats that keel over at the first sign of trouble.

And a lobster with a split personality.