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NARRATOR: This time on "Stranger Than Nature"...
200 rocks are creeping unseen across Death Valley, California.
MAN: There's a rock out there that they estimate, I think,
is the size of a washing machine,
and it's moving.
There's trails behind it.
NARRATOR: They're moving themselves.
WOMAN: This rock traced a trail
that makes a right turn and a left turn.
I'm liking this one.
NARRATOR: A serial killer strikes without warning
on New Zealand's beaches.
MAN: It was a real "whodunit."
Why were these dogs becoming so sick, so quickly?
MAN: There was enough lethal toxins on that beach
to kill perhaps 2,000 people.
NARRATOR: And in Namibia,
the world's fastest wild cat suddenly can't kill.
WOMAN: Definitely a mystery.
Over all the animals that I'd ever worked on,
I'd never seen anything like this.
NARRATOR: For the cheetahs, it's now or never.
Find out the answers to some of the world's weirdest mysteries
on "Stranger Than Nature."
Racetrack Playa,
Death Valley, California.
A 3-mile-long dry lakebed.
This inhospitable landscape
is the hottest and driest place in America,
yet something strange is happening
in this isolated desert.
Nearly 200 rocks,
from small stones to bulky boulders,
are creeping across the playa,
leaving trails behind them that stretch for hundreds of feet
across the hard sun-baked surface.
But nobody knows what makes the rocks at Death Valley
move by themselves.
MAN: How do you move a rock this big
that kind of distance?
NARRATOR: Geologist Paula Messina
has spent 16 years following the movement of the rocks.
PAULA MESSINA: There's something about the solitude here
and there's something about the mystery of it
that I really find intriguing.
NARRATOR: Around 200 rocks
are moving in different directions
within the 6-square-mile basin.
Some reach speeds of 4 miles per hour.
They rotate, spiral, and zig-zag back and forth,
carving tracks up to half a mile long.
PAULA: So this rock traced a trail
that makes a right turn and a left turn
and another right turn.
It makes one final left turn,
and the terminus seems to be over here.
NARRATOR: The rocks move independently of each other,
sliding in random patterns.
PAULA: And these are really close to 90-degree angles,
so...I'm liking this one.
NARRATOR: Physicist Bruce Borrowman
is obsessed by the enigma of the moving rocks.
BRUCE BORROWMAN: It is surreal.
It feels like you're almost on a different planet.
It's overwhelming.
There's a rock out there that they estimate, I think,
is the size of a washing machine,
and it's moving.
There's trails behind it.
NARRATOR: Even with almost 60 years of study,
no one has ever seen these boulders move...
Not even long-time park ranger, Jim Unruh.
JIM UNRUH: I came out here on a patrol,
checked on the rocks, and everything looked fine.
And I came back four days after that,
and there had definitely been rock movement.
PAULA: These rocks move when nobody is looking,
'cause no one has ever witnessed them in motion.
And yet we have evidence that they're moving
because they leave trails.
NARRATOR: The moving rocks of Death Valley
were first recorded by gold prospectors
in the early 1900s.
Nearly a century later, they remain a mystery.
JIM: Some visitors thought
that by virtue of this national park's proximity
to areas like the Nevada nuclear test site
or Area 51,
that there was some residual effect
that perhaps made these rocks move.
MAN: There's a lot of conjecture--
everything from magnetism to space ships.
MAN: Ships of an alien source are approaching from the sky.
Radio contact has been attempted,
but cannot be established.
WOMAN: Some people say extra- terrestrial things have gone on.
WOMAN: People are always talking about aliens around here,
because we...I've seen a UFO.
[barking]
WOMAN: I know the Earth holds a lot of secrets.
Maybe it's the big man upstairs.
NARRATOR: Some think supernatural powers
are also behind mysterious crop circles
appearing in the English countryside.
Many have turned out to be the creations
of self-confessed pranksters,
who sneak into fields in the dead of night.
But it would take someone of super-human strength
and incredible cunning
to drag heavy boulders across Death Valley.
BORROWMAN: If people are going out and pushing these along,
it would just leave these scraped gouge lines
in the surface.
You go to the playa and you look at the rocks--
it's not scrape marks across the top.
They're kind of little channels rather than scrapings.
NARRATOR: With no signs of pushing or dragging,
observers search for anything suspicious.
JIM: In my career as a National Park ranger,
I've been trained to look for physical evidence of tampering
and that sort of thing.
I've found nothing of the sort here.
This is no hoax.
NARRATOR: They eliminate foul play.
Then investigators consider what other forces could be at work.
BORROWMAN: One of the things that was first suggested
about the movement of the rocks on the playa
was that it was actually gravity moving them downhill.
In actuality, the playa's relatively flat.
The north end is just somewhat slightly higher
than the south end.
So they're actually moving just slightly uphill.
NARRATOR: Gravity can't push the rocks up a slope,
so they focus on other natural forces.
Energy fields deep inside the earth could hold a clue.
Molten metals in the earth's core
create a huge magnetic field,
turning our planet into a giant magnet
with spectacular and unpredictable results,
like the northern lights.
Racetrack Playa sits near a volcanic crater.
Erupting volcanoes can produce iron-rich rocks,
such as magnetite.
One theory suggests the planet's shifting magnetic field
could be pulling the rocks along these puzzling paths.
BORROWMAN: The reason this was suggested as an idea
is because the rocks make zigzag trails across the playa,
and as you can see, I can make this piece of magnetite
do zigzag patterns with my little magnet here.
This is all great and good,
however on the playa, the rocks are not magnetite.
They're not iron ore.
They're dolomite.
NARRATOR: Dolomite is a type of limestone
that carries no magnetic charge.
BORROWMAN: And if I try this same thing
with my piece of dolomite,
I get no magnetic attraction at all.
NARRATOR: The rocks aren't being guided
by invisible magnetic forces.
Something else must be moving them.
The investigation looks to Death Valley's unique landscape
for answers.
PAULA: Because there are mountains around here,
the wind is going to get funneled
through any crevice that it can,
so here at the center of the playa,
the winds can be moving in any direction.
NARRATOR: Wild wind patterns
could account for the twisted trails on the ground.
PAULA: In a 15-year period,
the rocks had moved predominantly to the northeast,
and then as of last year,
had started moving down toward the southwest,
and that's very typical of wind processes like dunes.
Dunes migrate one direction and another,
and these rocks are doing the same thing.
NARRATOR: To test this wind theory,
Bruce builds a homemade wind tunnel in his garage.
BORROWMAN: Crazy as it sounds,
I pulled the leaf blower out of the shed,
and I built a chamber.
And now I've got my wind tunnel.
NARRATOR: Bruce's mini playa allows him to find out
if air currents are the culprits.
BORROWMAN: One of the problems people had with the wind theory
is that they didn't believe that the wind theory
explained the zigzag patterns.
People don't realize that wind is so dynamic in and of itself.
This one, instead of just going straight through the chamber,
actually starts out and then veers off to one side.
So as the wind starts to work on the rocks in the playa,
we find that it can move these rocks all different directions.
NARRATOR: It seems like a breakthrough,
but the evidence doesn't stack up.
It would take wind speeds of over 150 miles per hour
to move some of the larger rocks.
PAULA: You can have hurricane-force winds
coming up through this playa,
but the surface here is really rough
and the biggest rocks are about 700 pounds.
So it would be very difficult to envision a wind
that could be that strong
to set something 700 pounds into motion,
given the nature of the surface.
NARRATOR: Further tests on a rough surface
put the wind theory to bed.
BORROWMAN: I had a test bed of clay,
put my rocks on there and turned on my leaf blower,
and I couldn't move any rocks.
Not a whole lot of action going on here yet.
And I felt comfortable
that I had determined it wasn't just the wind.
So I thought, "Well, that's it.
There's got to be something else."
NARRATOR: But what else could it be?
NARRATOR: The mystery just won't quit.
The alien landscape and strange happenings at the playa
even attract the attentions of NASA.
Planetary scientist Brian Jackson
starts to study the site.
BRIAN JACKSON: I've been observing the playa
over several years.
Seasonally we'll come up
and deploy weather monitoring equipment
and time-lapse cameras
to photograph the conditions on the playa.
NARRATOR: NASA's monitors
record vital evidence at the scene.
BRIAN: In the summer,
Racetrack Playa you can see, is just bone dry.
In the winter, however,
you get rain washing down from the mountains
and gathering on the playa,
so it can be quite wet in the winter.
The playa surface,
instead of being this sort of hard-packed clay,
will turn into this sort of goopy peanut-buttery substance.
It can be actually quite slick.
NARRATOR: The texture of the surface
could be a significant clue.
BORROWMAN: You're familiar with putting oil on something
to make it slipperier.
You put oil in a pan before you cook
to make them so they don't stick.
NARRATOR: Bruce uses his test bed
to simulate the wet surface of the desert in winter.
This time he sees results.
BORROWMAN: My rocks started moving in my little test bed,
and I was so excited. That day was just so fun.
It was exciting.
NARRATOR: But NASA scientist Brian
still believes there's more to discover.
BRIAN: This is a big chunk of dolomite rock
that came out of the cliffs over there.
You can see just by the size and me...
[grunt] tugging on it,
it's probably a couple hundred pounds.
The cliffs are a couple hundred meters over there,
so how do you move a rock his big
that kind of distance?
NARRATOR: In the hottest spot in the U.S.,
Brian thinks an unlikely element is at work--
ice.
BRIAN: All indications are
that the rocks move primarily in the winter.
In the winter on the playa, it rains,
water pools up and then freezes,
because the temperatures get pretty low.
When the playa gets wet and freezes,
these ice collars can form around the rocks
and help to buoy them up,
basically reducing friction between the bottom of the rock
and the surface of the playa.
So you can move the rocks around very easily
with even very light winds,
so they drag like a boat with its keel
in the surface of the playa and leave these tracks.
NARRATOR: Brian thinks water, wind,
and freezing temperatures combine
to produce a rare natural phenomenon.
Rainwater turns the arid basin into a shallow lake
that freezes in winter.
Ice forms around the base of the rocks.
As the lake thaws, the rocks remain frozen.
Collars of ice lift the boulders off the clay bed,
allowing even light winds to move them.
As the ice thaws, the rocks gradually sink,
and as they sink,
they slide along the wet clay, leaving trails behind them.
BRIAN: So we can see a trail
that was probably left by an ice floe here.
You can see that the trail is pretty wide here,
and it kind of narrows as you move into this direction.
So that suggests, for example,
that the ice floe that was making this trail
may have been melting and narrowing as it moved.
BORROWMAN: People would say, "Frozen in Death Valley?"
On an average, the playa will freeze 50 nights a year.
So we think of Death Valley as this hot...
but in the winter time at night,
subfreezing temperatures are common.
NARRATOR: The wild weather extremes of Death Valley
combined with an alchemy of rock, wind, and ice
create an extraordinary event.
BORROWMAN: The wind, the water, the freezing temperatures,
rain, high-speed wind...
we've got rock movement.
NARRATOR: Scientists and tourists visit all year round.
But for some reason, nobody has ever seen the rocks moving.
Until they do, the mystery remains.
PAULA: One of the reasons that I love this place so much
is because it's so romantic,
and the fact that I've never seen the rocks moving
and no one else has ever seen the rocks moving
makes it that much more intriguing.
I don't really want to see the rocks in motion.
It would be like giving away the punch line of a joke.
NARRATOR: This case remains under investigation.
New Zealand.
Auckland,
city of bays, boats, and beautiful Pacific beaches.
And a detective story that begins with a dog.
Jenni McManus enjoys a walk with her young boxer pup, Rocky,
at the water's edge.
JENNI McMANUS: I bring Rocky down quite regularly,
let him run around, play with other dogs.
It's very good socializing for them down here.
NARRATOR: It's the perfect playground
for a carefree canine to explore.
JENNI: He's an extremely inquisitive dog.
He snuffles constantly down on the beach.
He's snuffling in the rocks, he snuffles at home,
he snuffles just about everything.
He's a very loving, lovable dog.
[barks]
NARRATOR: One minute, Rocky is his normal self,
but the next minute, everything changes.
JENNI: I noticed that he was foaming at the mouth
and his back legs were sort of shaking
and almost giving way underneath him.
NARRATOR: Unknown to Jenni,
Rocky is about to become swept up
in a sinister and baffling mystery.
JENNI: I just couldn't imagine
what had possibly happened to him.
NARRATOR: Rocky is deteriorating rapidly.
Within minutes, he's unable to stand.
Jenni fears for his life.
JENNI: It was obviously serious,
so I tossed him in the back of the car
and took him round to the vet's.
NARRATOR: At the nearest animal hospital
veterinarian Neil Waddell assesses the casualty.
NEIL WADDELL: Rocky was looking very unhappy,
He was hunched up, vomiting profusely, drooling,
and just looking really miserable and in pain.
NARRATOR: The symptoms are an enigma.
NEIL: At that stage, we were not sure what was happening.
It didn't really fit in with anything in our experience.
NARRATOR: Neil has little idea
of what could cause such severe vomiting and collapse.
He performs an emergency operation.
Rocky's life is on the line.
Back at the beach,
other dog owners also see their beloved pets in serious trouble.
Rachelle O'Born's new puppy, Roxy,
is struck down at the same place as Rocky.
RACHELLE O'BORN: Literally out of the blue,
like she was playing and happy,
and the next minute, she just looked up at me
and started to cowl and put her tail between her legs.
NARRATOR: David Willetts' puppy George
also starts to show worrying signs.
DAVID WILLETTS: At first I thought it was a bit of nylon
hanging out of his mouth,
but it was just a thin bit of drool.
And I knew straight away that he wasn't feeling the best.
NARRATOR: They all display similar symptoms.
RACHELLE: And then she was just vomiting all the way home,
and it was probably, you know, about 200 meters,
just vomiting the whole way.
NARRATOR: Both dogs are getting sicker by the second.
DAVID: Vomiting,
losing control of, you know, his bowels,
and then he started to exhibit early signs of paralysis.
NARRATOR: Inside 24 hours, Roxy recovers,
but George, just a puppy, isn't so lucky.
DAVID: It was just so hard to comprehend
that such a strong, healthy young dog
died so fast.
MAN: Grant speaking.
NARRATOR: Reports of dogs suffering identical attacks
reach city council investigator Grant Barnes.
GRANT BARNES: Thank you, Dr. Schwartz.
Soon after going down to the local beach,
the dogs had become sick
and were either vomiting,
were frothing at the mouth,
and becoming generally very unwell
in a short space of time&.
And where's the dog now? Have you taken it to the vet?
NARRATOR: A pattern is emerging.
GRANT: That's terrible news.
REPORTER: The Auckland Regional Public Health Service
has issued a warning to the public, especially...
REPORTER: Public health officers
say children and pets must be supervised...
REPORTER: The results of tests
on one of two dogs that have died...
GRANT: This issue was running headline stories
pretty much every day,
so it was really apparent in locals' minds
that we had an issue of considerable concern
in Auckland.
NARRATOR: There's an unknown killer at work in Auckland,
and residents are starting to panic.
GRANT: People wanted answers.
They wanted to know were the beaches safe,
could we swim, could we fish, could we kayak?
Could we do the normal activities
that Aucklanders take for granted?
NARRATOR: The case is spiraling out of control,
and now it's looking like dogs are only the first of many.
On the same beaches,
marine animals are washing ashore as corpses.
GRANT: We were seeing penguins, dolphins, fish--
all for some reason stranding on Auckland beaches.
Now, during normal times, particularly in winter,
that's not necessarily unusual.
What was unusual was that it was all in the space of two weeks.
NARRATOR: Grant and his team call for help.
Caleb King from New Zealand's biosecurity unit responds.
CALEB KING: We did have to explore the possibility
that the fish deaths and the dog deaths
were somehow related.
The first thing we suspected
was this being a marine algal event.
NARRATOR: Marine organisms may be microscopic,
but they can cause big problems when they unleash toxins.
Millions of algae cells combine to form harmful blooms
stretching for hundreds of miles across the ocean surface.
A toxic tide can become lethal to sea life, birds, and mammals.
GRANT: It had been quite stormy in Auckland,
and we were getting high waves pushing large algal mats
up onto the high tide mark.
Some algal species contain toxins
that dogs are particularly sensitive to.
NARRATOR: The team collect water samples for analysis.
GRANT: They came back negative.
CALEB: There was no evidence of a significant algal bloom.
NARRATOR: Their first and only suspect
they've already eliminated
GRANT: So within a couple of days,
we had no further understanding of what was going on,
other than dogs were continuing to get sick.
NARRATOR: Rumors run riot.
Some people point the finger at a nearby uninhabited island.
Rangitoto is an extinct volcano five miles from Auckland.
It rose from the ocean depths just 700 years ago,
and it harbors a dark scurrying secret.
Rats infest this wildlife preserve,
and they're not welcome.
In the battle to eradicate them,
the chief weapon is a death-dealing poison
called Brodifacoum.
Phil Brown is the man charged with turning the island
into a rat-free zone.
PHIL BROWN: We apply the bait often with a helicopter,
and we use differential GPS,
which gives us an extremely accurate way of laying the bait
so we know where all the baits have gone,
and we make sure that the bait covers the entire island.
NARRATOR: But some think the deadly drop
has drifted into the water.
PHIL: We do what we can
to minimize Brodifacoum getting into water,
but of course it's always possible
that some pellets end up in the water.
NARRATOR: Could the poison pellets
have made it to the mainland,
with fatal results?
PHIL BROWN: We were testing a range of animals
that the public were concerned
might have been poisoned by Brodifacoum,
and we were finding no traces of Brodifacoum in those animals.
NARRATOR: Things get worse.
Hundreds of fish and increasing numbers of penguins and dolphins
are struck down.
Nearly twenty are ill.
Six dogs are already dead.
GRANT: It was a real "whodunit."
What was going on?
Why were these dogs becoming so sick, so quickly?
NARRATOR: Poison expert Paul McNabb joins the team
tackling this deadly detective story.
PAUL McNABB: Really no one had any idea what was happening.
I just wanted to come up and have a look
and see whether or not
there was anything that I could add to the investigation.
NARRATOR: Paul's plan
is to go back to the scene of the initial outbreak
for more clues.
PAUL: The problem with dogs
is they like to get into smelly things.
NARRATOR: A dog's sense of smell
is a thousand times more powerful than ours.
Smell supplies dogs with more information than sight,
and they use this sense to build a picture of their surroundings.
CALEB: We went to the beach to collect specimens,
just to see, "If I was a dog,
what would I be looking at and smelling and eating?"
and try and find those things and look for the toxin
on the things we could find on the beach.
PAUL: And we picked up
around about 70 or 80 things from the beach.
We took all of those back to our lab,
and then we just worked through
from those that we felt were most likely to be involved
through those that were least likely.
NARRATOR: Paul's team hopes that their widespread search
holds the key to the killer's identity.
They're setting themselves a mammoth task.
GRANT: There is a vast array of compounds
that exist in the environment
that could, under certain circumstances,
cause an illness in dogs and potentially humans,
but where do you start?
It was a case of working through from A through to Z.
NARRATOR: With so little time and so many samples,
Paul uses mice to test for signs of toxins.
PAUL: By the time we had given our eighth sample,
we knew that we'd found a very toxic item.
NARRATOR: The effect is immediate.
PAUL: That mouse died within seconds.
NARRATOR: The source of this deadly sample
is completely unexpected.
PAUL: The sample was a sea slug.
NARRATOR: The gray sea slug is a New Zealand native
and has been heavily researched,
but it's greatest secret has remained hidden until now.
PAUL: Really, through all those studies,
people had completely missed the fact that it was toxic.
NARRATOR: The poison in the sea slugs, tetrodotoxin,
is 1,200 times more powerful than cyanide.
There is no known antidote.
GRANT: These are one of the most potent, poisonous,
toxic substances you can think of,
and here they are in a sea slug just outside our doorstep.
NARRATOR: Tetrodotoxin is the lethal poison found in blowfish.
Thrill-seekers eat this sushi delicacy,
but for up to six people in Japan each year,
it's their last ever meal.
The poison paralyzes its victims
while they remain fully conscious.
Anything eating the sea slugs would suffer the same fate.
PAUL: So it only takes 1 to 2 milligrams of tetrodotoxin
to kill a person,
and these slugs were 10 to 20 grams in size.
And on that first day,
when we went there and collected slugs from the beach,
we found around about 200.
So there was enough tetrodotoxin on that beach
to kill perhaps 2,000 people.
NARRATOR: Samples from the dog's stomach
test positive for the presence of tetrodotoxin.
The team have identified the killer.
But the method of delivery remains a mystery.
CALEB: We couldn't get a consistent report from anybody
about what the dogs had eaten prior to starting to vomit
and showing clinical signs,
and none of the dogs at the post-mortem
had sea slugs inside them.
There was still this disconnect
between here's the poison, here's the sea slug,
but how's the dog getting it?
NARRATOR: The scientists are missing a vital connection.
PAUL: We took these slugs and put them into aquariums
so we could study them in a bit more detail,
and we found they're prolific layers of eggs,
and when we tested these egg sacs,
we found those were very high in tetrodotoxin also.
NARRATOR: Could these highly toxic eggs
be poisoning the beaches?
PAUL: Seaweed is a possible place
where the eggs may get laid,
and if the seaweed was washed up on the beaches,
it may be that the dogs had come in contact with the eggs,
and therefore tetrodotoxin.
NARRATOR: With storms washing seaweed onto the sand,
the beach was rife with exciting smells
to entice a curious canine.
JENNI: Rocky came flying down onto the beach,
he was straight into the seaweed,
he was snuffling it, he was chewing it,
he was bouncing around it, he was trying to dig into it.
He was sniffling around with whatever he could find.
NARRATOR: A quick snuffle could be a dog's last breath.
PAUL: If an owner sees a dog sniffing around at something,
it could be too late.
Because the tetrodotoxin is so high,
it only takes a very quick bite
or a few seconds in the mouth
of swallowing a small amount of slug or egg sac,
and that dog will have become exposed to a lethal dose.
NARRATOR: Rocky was one of the first victims
of the killer slugs,
and he's one of the lucky ones.
Just a week later, he's back on his feet.
JENNI: When, you know, I saw the fate
and heard of the fate of other dogs in the area
who weren't so lucky as Rocky, it was, you know...
I think he's a charmed dog, he's a magic puppy.
Africa,
Namibia,
Okonjima Nature Reserve.
This vast wilderness
is home to many of Africa's wildest animals,
but it's also a vital hunting ground
for the world's fastest land mammal,
the cheetah.
This high-performance hunter
is a lethal mix of speed and agility.
It attacks like lightning,
accelerating as fast as a Ferrari.
NARRATOR: But these already endangered cats
are in crisis.
Experts examine them
and find that nearly three-quarters of their cheetahs
have a mystery condition
that could threaten their very existence.
AJ Rousseau has been observing cheetahs here
for almost six years.
He's been tracking one male in particular,
observing him make a kill every three days.
NARRATOR: Failing to make a kill only leads to one outcome.
NARRATOR: Nearby, other cheetahs begin to act strangely.
WOMAN: Definitely a mystery.
Of all the animals that I'd ever worked on,
I'd never seen anything like this.
NARRATOR: Biologist Dr. Laurie Marker
sees more and more of them lose their hunting skills.
LAURIE MARKER: There was something going on,
and so I started saying, "What kind of diseases are there?
What kind of issues are evolving?
Could it be a genetic problem?"
NARRATOR: Initial observations reveal a significant connection.
Many of the cheetahs are losing their most critical sense.
WOMAN: For a cheetah, it's all about sight.
It is so important
because of this unique technique that the cheetah uses.
They need the long-distance sight
so that they can actually decide on what they're going to hunt,
and then the charge starts.
NARRATOR: The cheetah's large eyes
can spot prey over three miles away.
They detect even the slightest movement.
Black tear lines beneath each eye
reduce the glare of harsh sunlight.
Even football players use this trick.
Any hunter that can't spot prey is heading for disaster.
The cat AJ is tracking has just that problem.
LAURIE: We actually saw multiple animals
where they were very hazy-eyed and blinded.
I just kept calling it "the hazy eye syndrome."
LAURIE: Why? What is going on here?
What was doing this?
NARRATOR: It's becoming an epidemic.
Mysterious eye problems
are sweeping through the Namibian cheetah population.
Unfortunately for the scientists,
wild cats make for dangerous patients.
Dr. Gary Bauer specializes in veterinary eye care.
GARY BAUER: The first time that we were there
we examined in the region of about 46 cheetahs,
and of those 46,
we had a 23% incidence of cataracts.
NARRATOR: A cataract is a clouding of the eye,
caused by infection, trauma, diabetes,
or inherited disorders.
Cataracts form in humans, cheetahs, and other animals,
when a chemical change in the lens
creates a milky white fluid
that blocks light to the back of the eye.
They can lead to complete blindness,
with devastating results.
GARY: It was surprising, and it was alarming.
If you look at a cheetah's normal life expectancy,
you can probably look at anything
between 10 and 14 years.
I think the mean average
of the cheetahs that were affected with cataracts
was about 6.5 years of age,
and that could have a significant effect
on the population as a whole.
NARRATOR: They need to find out
what's attacking the otherwise healthy cheetahs.
Donna Hanssen has a prime suspect.
DONNA HANSSEN: Cheetahs react to anything that moves.
So they're always inquisitive,
and a snake moving past them
would definitely rouse the curiosity of a cub.
NARRATOR: Namibia is home to three species of spitting cobra.
These snakes fire venom from their fangs.
Their preferred target is the eyes.
NARRATOR: This venom attack could blind the cheetahs.
Gary re-examines the cheetah's eyes.
He sees no evidence of chemical burns from venom.
But what he does find proves to be a crucial clue.
GARY: We had a 74% incidence of traumatic corneal injuries--
in other words,
full-thickness-penetrating scars into the cornea.
NARRATOR: Most of the cheetahs they examine
have scratches or slashes on their eyes.
Something solid and sharp is attacking them.
DONNA: All of a sudden, nearly every cheetah
had either a chip or a cut or a cataract developing.
And this is what started this big question:
where was this injury coming from?
NARRATOR: Gary finds cuts and grazes on the cornea,
the outer protective layer of the eye.
Something is striking at the delicate membrane.
But what?
Cheetahs weigh just 140 pounds.
They hunt a number of fierce animals.
Half the time, their prey escapes.
And when cheetahs take on large prey like this kudu,
they risk their vulnerable eyes.
DONNA: It's those horns, the kicking...
the cheetahs are not doing it quickly.
NARRATOR: Other big cats also attack dangerous prey,
yet they show no sign of eye damage.
So there must be something else.
On a good hunting day,
a cheetah can take in nearly 24,000 calories.
That's 12 times the daily average for a human.
To achieve this, cheetahs often hunt in groups,
and they are highly competitive.
AJ thinks this gang behavior
might be to blame for their injuries.
NARRATOR: When unrelated gangs confront each other,
battles break out.
DONNA: The fights between cheetahs
that don't know each other are vicious.
I saw a cheetah
physically trying to destroy the other cheetah
by going for its stomach.
NARRATOR: Leopards, lions, and domestic cats
can draw their claws back completely,
but cheetahs can't do this.
Their deadly claws are permanently exposed.
In a chase, they act like spikes on a sprinter's shoes.
But in a fight, drawn claws become a razor-sharp weapon.
GARY: If you get a claw or a tooth going into the eye,
then that is catastrophic to that eye.
And the end result of those types of injuries
are either a shriveling-up of the eyeball itself,
or what we call a glaucoma,
where the pressure starts building up,
and eventually you get an eyeball that is blind,
and visual restoration is not a possibility in those at all.
NARRATOR: Hunting injuries or fights over territory
would have to be very frequent
to affect the eyes of so many cheetahs.
GARY: These ancillary injuries, or other injuries--
claw injuries, bite injuries--
are fairly insignificant in the total population.
In all the cheetah that we saw, there were only two animals
that had an eye that was damaged to that extent,
which we could put down to either a claw injury or a bite.
NARRATOR: Spitting cobras,
fights with other cheetahs,
and struggles at kills are off the suspect list.
The team needs a new lead.
Gary makes a breakthrough in his surgery.
GARY: Essentially this photograph
shows an otherwise fairly normal-looking eye,
but with a 5-millimeter thorn stuck in the iris,
gone through the cornea,
and closed off from the body's immune system.
This photograph was the one that demonstrated to us
that a normally visual cheetah
was capable of injuring its eye to such an extent
that a piece of thorn actually breaks off in the eye itself.
NARRATOR: Incredibly,
it's not another animal attacking the cheetahs;
it's a plant.
LAURIE: It was like a "Eureka," an "Oh, my God! Yeah!
That just makes so much sense."
It became a link to a serious big problem.
NARRATOR: In Namibia,
a rampant thorn bush is taking over an area of land
almost the size of Colorado.
LAURIE: The animals that actually had eye problems
were coming from the same region,
and that was really fascinating to us.
And this bush encroachment
became sort of the obvious thing to start looking at.
So if we kind of look into here
and imagine what it's like for a cheetah to be hunting
at 110 kilometers per hour,
and all of these thorns
are pretty much at the height of the cheetah,
which is about, you know, 75, 78 centimeters in here.
Ouch!
NARRATOR: Wayne Hanssen
used to be a bush guide in this area.
He knows exactly how much damage these thorns can cause.
WAYNE HANSSEN: It is the only thorn
when you drive through this veldt,
and any farmer in Namibia will know,
it punctures tractor tires, truck tires.
There's nothing that it doesn't go through.
Well, a good example is using an orange
that is as close a resemblance as we have here to an eye.
It just goes straight in.
It's hardly an effort at all.
It's a matter of time before we get something like this in
and coming out and just going pass like that,
it's just right to the hilt and out,
and I mean, after that your eye's pretty much gone.
NARRATOR: They've caught the culprit,
but why are these thorns injuring only cheetahs' eyes
and not those of lions or leopards?
GARY: Their hunting habits are completely different.
Leopard and lion are generally mostly a stealth-type predator
with a little bit of speed and pounce at the end...
Whereas cheetah are predominantly
a stealth and a chase down.
NARRATOR: Lions and leopards lie in wait for passing prey,
but cheetahs chase down their prey
over hundreds of feet.
And with the added handicap
of a sight-clouding cataract or blinding trauma,
hunting through the thorn bush becomes impossible.
Cheetahs are the oldest species of big cat on the planet.
Yet after 4 million years,
a thorn bush is suddenly putting their survival at risk?
Wayne thinks he knows why.
WAYNE: The fastest change took place
when we started dividing this land into private property.
So you buy the farm, you fence it,
you put in a herd of cattle,
the cattle graze down the grass,
so with the grass gone, the bush has got free reign.
That is that encroachment that we talk about.
LAURIE: We've lost about 50% of our grazing land
from this thickened thorn bush.
The wildlife can hardly get into some of it,
the livestock can't.
So this thickened thorn bush is a huge problem.
Bush-encroached...
What the habitat used to look like.
And this is what we're trying to aim for.
NARRATOR: The team has solved the mystery.
And by restoring the hunting grounds,
the future for Namibia's cheetahs looks a lot brighter.