Costa Rica, Central America.
Home to one of nature's most spectacular events.
I'm here on one of the few beaches in the world where it's possible
to witness thousands of nesting sea turtles
as they arrive together to lay millions of eggs.
Despite their numbers, this extraordinary phenomenon
is one of the least understood in the natural world.
So, over the next eight weeks,
I'm joining a team of international scientists
on a mission to unravel the mysteries of this unique event.
I want to unlock some of the secrets that they still keep from us.
We'll use the latest technology to investigate how the turtles arrive
in such large numbers...
This is real conservation science happening right before me.
She might be our turtle.
..and reveal the challenges for the millions of eggs laid on the beach.
They are going to be destroying whatever nests
are already in the sand.
We discover the perils of their incubation.
I didn't think it would be this nerve-racking.
And in a world first...
Oh, look at that!
..we'll look inside a turtle nest...
This is the very instant of its birth.
..to reveal how unborn turtles may communicate...
Wow, that's really clear.
..and work together to hatch en masse.
I've never seen it before.
They're beautiful, aren't they?
Today, sea turtles are at a greater risk of extinction than ever before.
Understanding this unique nesting and hatching event
could help us better protect turtles around our planet.
So, join me over the next 90 minutes as we reveal the incredible secrets
of the turtle from inside the nest.
Sea turtles are one of the most ancient creatures on earth.
They've roamed our oceans for millennia,
and outlived the dinosaurs.
Some can live more than 50 years
and travel over half a million kilometres in a lifetime.
There are seven species of sea turtles,
but six are now at risk of extinction.
Our investigation will focus on
one of the most abundant but least studied - the olive ridley.
These turtles nest alone, but also en masse,
often in their hundreds of thousands.
The phenomenon is called "arribada", the Spanish word for arrival.
This is Ostional on the Pacific coast.
It is one of the most important nesting beaches
for olive ridley turtles anywhere in the world.
And that's because there are fewer than a dozen places
where you can see this mass nesting phenomenon,
and Ostional is one of the most impressive.
I've travelled 9,000km from the UK to Costa Rica in Central America.
Bordering both the Pacific Ocean and the Caribbean Sea,
this small tropical country contains a wealth of natural riches,
and almost 6% of the world's biodiversity.
It is home to over half a million species.
250 different mammals...
..almost 900 species of birds...
..and 225 reptiles,
including five of the world's seven species of sea turtle, which nest here.
The extraordinary mass nesting event can be split into six key stages,
and the first is when the females begin to assemble offshore
in their thousands.
Female sea turtles use the Earth's magnetic field
to navigate back to the beaches where they were born
to lay their own eggs.
Scientists believe these turtles learn
the unique magnetic signature of their birthing beach as hatchlings,
a process known as geomagnetic imprinting.
The arribadas take place roughly once a month
and, here on Ostional beach, the next one is due any day.
You know, it's really rather wonderful
knowing that they're gathering in what could be their thousands
just offshore.
Lead scientist Dr Roldan Valverde has built a unique hatchery
to examine what goes on inside a turtle nest in unprecedented detail.
Hatcheries are used to protect and study sea turtles.
But in this one, we've dug acrylic boxes into the sand
to house our technology.
For the very first time,
infrared cameras and lights will allow us to record the nest 24/7.
Basically, this is going to be one of the walls of the nest.
I'm going to dig a hole
that is going to resemble the chamber of the nest.
Once it is completed, we're going to be able to put
the entire clutch of eggs that we're going to collect from a turtle
that is nesting on the main beach.
So we can follow the entire incubation process.
A pioneering piece of tech called Turtle Sense
will monitor temperature and movement.
It kind of resembles a turtle egg,
but what we're going to do is bury it.
On this other end we're going to connect the sensor
to a communication tower.
Data will be sent via a mobile network,
and the readings accessed online.
Being able to deploy cameras inside a nest is brand-new to me.
It's very exciting because whenever I have dealt with nests,
it has been either at the time when they are being laid into the ground
or when the hatchlings are emerging to the surface.
Everything that has happened in between those two points in time,
I know virtually nothing about.
So, we're all set.
The turtles are coming and we're ready for them.
What a sunset.
You know, it's hard to believe that this deserted stretch of beach
could soon be a swarming mass of turtles.
I think it's going to be really exciting.
Well, it's half past ten and Roldan and I are heading down to the beach
to see if any turtles have started arriving.
We're using red-coloured head torches,
as turtles are less sensitive to red light than white.
It's almost midnight when we spot our first olive ridley on the shore.
This is a lone turtle,
providing us with the perfect opportunity
to collect her eggs ahead of the mass arrival of other females.
Solitary turtles are easily spooked when they dig their nests,
so we stay behind her.
But once she starts laying her eggs, little will bother her...
..so we can move in.
I'm just clearing the path so that I can get in there with the bag
and grab the eggs as they fall.
The female lays about 100 eggs
and drops two or three at a time.
She produces about 50 eggs
out of each ovary.
Each egg is about 4cm in diameter
and covered in mucus.
The shells are tough but flexible.
Look, she put... She laid eggs right next to another nest.
She took just a little more than 15 minutes.
I'm guessing she has a little bit more than 100 eggs.
So, we'll see when we put them in the hatchery.
It's a good clutch of eggs.
Our donor mother begins to cover her empty nest.
She uses her rear flippers to fill the chamber
then her whole body to compact it down.
She's going to go through that,
bringing more sand, thumping, more sand, thumping.
Then she's going to be using her front flippers
to bring more sand around
and on top of the nest, she's going to thump again,
and at some point she's going to stop thumping
and then she's just going to spread the sand at the top,
sort of to conceal completely the area where the nest is located.
Each female spends between 20 and 40 minutes covering her tracks.
This is vital to prevent predators like humans, vultures and dogs
from finding her nest.
They are very good at doing this,
they are probably the species that does it the best.
Once she's done,
you could barely see that there was a nest in that area.
With her eggs in our custody, the female disappears back to the ocean.
Well, this is what it's all about, this is a turtle egg,
and it's about the size of a ping-pong ball.
It's got a tough, flexible outside.
Inside the egg is an embryo the size of a pinhead.
And the rest of it is yolk, food supply,
which will allow that embryo to develop into a baby turtle.
Right...
At the hatchery, our priority now
is to bury the clutch of eggs in the safe environment of the sand.
This one is going to be a lot of sand taken out.
I think you're making a great job, there.
A turtle would be proud of that.
We're going to count the eggs as they go in
so we can compare it to the number of baby turtles that come out.
15...
Just like a real olive ridley nest,
we're burying our clutch of eggs 40cm deep
in cool, damp sand.
103.
And... 104.
That's it. And the hi-tech egg, which, of course,
is very important...
We position the fake turtle egg sensor on top of the other eggs,
where it will monitor temperature and detect any movement beneath.
I'll just hold it in place while you...
I bury it? Yeah.
That's 104 eggs... 104.
..safely buried in our nest.
And now all we have to do is connect the other end of this...
To the communication tower.
..and then that's it, a good night's work.
We're done.
We spend a few more hours on the beach
hoping for the arribada to begin.
But when no more turtles arrive, we decide to call it a night.
But in this magical place, you don't have to wait long.
Around once a month,
Ostional beach plays host to one of the most impressive events
in the natural world.
The flotilla of waiting turtles advances closer to shore...
..and the second stage of the mass nesting event begins...
..the arribada.
The mass arrival starts with a few silhouettes on the shore.
Numbers build throughout the night.
But the most arresting sight is at dawn.
I remember the first time I saw an arribada.
It looked like the beach was packed with rocks.
Then the rocks started moving,
and then I realised that these things were turtles.
Everywhere.
In peak season, numbers range from 50,000 to 300,000 animals.
The largest arribada ever recorded here
was just under half a million turtles,
which would mean up to 50 million eggs could have been laid.
The main explanation for why arribada develops has been that
the high number of nesting females
prevents a high impact of predators on the population.
So, basically there is safety in numbers.
It takes between two and five days and nights
for all the females to nest.
And this month, 178,000 turtles came ashore to lay over 17 million eggs.
As the arribada ends,
some turtles will return to nest again a month later,
but most will begin their migration away from Ostional
to feed in the vast Pacific Ocean.
Inside our nest, the cameras have started recording
and Roldan and I can take our very first look at the footage.
Oh, my goodness. That's great!
That's a really cool shot of the inside of the nest.
Very sharp. Sharp as a tack, isn't it?
This image is so clear, it's so fantastic.
And we're going to be able to see those little hatchlings
actually breaking out of those eggs.
Exactly.
Is that the first time you've ever actually seen these?
It's my first time, yes. Very nice. Wow!
One of the most critical elements
that we must monitor inside the turtles' nest is the temperature,
which is vital to ensure the embryos survive.
So, they develop properly between 26 and 35 Celsius.
Below 26 or above 35, the embryos tend to die.
Now, we have measured incubation temperatures here on the beach.
In the dry season we know that
incubation temperatures exceed the upper limit,
and so, because of that,
most of the embryos here on Ostional, they die.
Our eggs WILL be incubating as the hotter, dry season begins.
So, to prevent a potentially fatal rise in temperature,
we've secured a shade cloth over the hatchery.
Temperature can kill but, remarkably,
it also determines whether the hatchlings are male or female.
If the nest incubates at warm temperatures,
it's going to produce mostly females.
If it incubates at lower temperatures,
it's going to produce mostly males.
Where is the half and half point, half males, half females?
Right - for this species it's between 30 and 31 degrees,
and you tend to get about 50-50 at that point.
This sex determination also occurs in other reptiles,
including crocodiles and some lizards.
The embryos of these animals lack sex chromosomes,
so gender is determined during incubation
by the ambient temperature of the nest.
When we first put the eggs in the nest, the temperature was about 26,
which is the lower limit of development for the embryos.
Since we closed the nest, the temperature has gone up.
It has been fluctuating between about 28-30 degrees inside the nest,
which is good.
Well, I cannot wait to see what happens when these guys hatch out.
It's very exciting, yes.
Our eggs are likely to take between 45 and 50 days
until the hatchlings emerge, depending on the temperature.
But we'll have a better idea around day 40.
The impact of rising incubation temperatures in our warming world
is of grave concern to turtle scientists.
Embryo deaths are likely to increase
but, because temperature determines gender,
so, too, are the number of female-only nests.
Recent research shows that in Australia,
in one of the world's largest populations of green sea turtles,
99% of immature turtles are now female.
Eventually, there may not be enough males to fertilise all the eggs.
Some populations could go extinct.
Roldan believes that most baby turtles hatched on this beach
are also female, due to the high temperatures
and numbers that return here to nest.
One of the unsolved mysteries of the mass nesting event
is what triggers the females to come ashore.
The first scientist to investigate this is Vanessa Bezy.
She analyses turtle behaviour in the water and from the air.
Deploying a drone allows her to see what happens
before an arribada begins.
I fly five different transects that are perpendicular to shore
and 3km into the ocean,
taking a video and later analysing it using behavioural software
to look at where each individual turtle is in relation to shore
and then looking at how many turtles we have
and how close to shore they are.
What we've observed is that we essentially have sea turtles
in the water here year-round at Ostional.
The densities of turtles in the water
are much higher than most places in the world.
Typically we see a staging area about 2km out.
And the number of turtles slowly builds
in the days leading up to a mass nesting event
and they slowly move towards shore.
This is the first time this type of data
about how an arribada begins has been collected.
Over the year-long study, I flew over 100 different surveys,
consisting of over 500 flights...
..and in that time we counted over 22,000 turtles
at the surface of the water.
But what are the turtles doing before they come ashore?
Essentially the turtles are just surfacing to breathe and resting,
and then they're diving again and resting at the bottom
until they come up to nest.
The more we understand what is happening in the water
in front of the beach, the better we'll be able to understand
what are the main cues that are triggering the arribada behaviour,
and that is very exciting.
Most theories about how the turtles synchronise their arrival onto land
suggest environmental cues like the moon phase,
offshore winds or even rainfall.
Arribadas usually begin about a week before a new moon,
and Vanessa believes that the trigger
might also be linked to pheromones.
A pheromone is a chemical signal that an animal uses to basically
interact and impact the behaviour of other animals of the same species.
So, it's possible that sea turtles, like other animals,
are using this type of chemical
to communicate and to synchronise nesting behaviour.
To investigate this, the team pick turtles close to the shore
to bring them onto the boat.
Weighing up to 50kg, this is no easy feat.
Pheromones are detected using smell,
so Vanessa wants to temporarily block this sense.
If these turtles don't join the arribada
at the same time as the others, it could be because
they can't detect the pheromone signals to do so.
I'm going to squirt zinc sulphate into her nostrils.
So, I have to reach into her mouth.
She treats the turtles with zinc sulphate,
a harmless numbing agent, which will wear off.
She then tracks the turtles to investigate whether this affects
their ability to join an arribada,
with some interesting preliminary results.
My study is basically just scratching the surface of trying to
unravel the mystery of the mass nesting events.
What we found is that the turtles that didn't have a sense of smell
were nesting about a day later.
So, this supports that idea that the turtles need some chemical signal,
some odour, to help trigger the synchronisation.
Another key part of our investigation is finding out
where the females go once they've laid their eggs
and left the arribada beach.
Scientist Christine Figgener attaches satellite transmitters
to the turtles during the nesting season
to track the migration routes.
Every time I see a sea turtle nesting,
I just have to remind myself,
these animals have been around for millions of years.
I'm sitting here with a dinosaur, somebody that might have seen...
At least the species has seen the dinosaurs.
It's just incredible.
Once the turtle has laid her eggs,
Christine uses an ultrasound to identify whether the female
has finished laying eggs for the season.
If she has, it means she will travel away from the beach,
giving Christine the data she needs.
She laid all her eggs.
She might be our turtle.
That is awesome.
Well, it looks like I've arrived right in the middle of something
really interesting. This is absolutely fascinating,
this is real conservation science happening right before me.
Covering the turtle's eyes helps reduce stress
and also allows the team to switch into brighter light.
The turtle shell, known as a carapace,
must be smooth and free of algae
for the transmitter to attach successfully.
So, now I'm using a little bit of sandpaper to get her shell smooth.
The carapace is made of keratin,
the same substance as human hair and fingernails.
It renews throughout the turtle's life,
so the transmitter will eventually drop off.
A strong, fast-drying epoxy secures it into position.
A second coat seals the transmitter on to the turtle
to ensure it remains waterproof.
It takes 45 minutes to dry.
Now, how long will this device actually work for?
Yeah, hopefully about a year.
That would be the ideal situation.
So, when this thing works,
how do you receive all the oodles of information it transmits?
Well, nowadays, of course I have an app on my smartphone and...
Hold on, you can track this day by day, hour by hour,
on your smartphone?
Yes, I can literally sit in my bed, wake up in the morning,
and first thing I do is I check
what my turtles have been up to the past days.
That's really great. Yeah.
You can just go, "Let's see who's... Oh, she's doing well!"
Yeah, exactly. All of that will be available.
What will all this reveal to you?
If we are able to figure out what are the routes that are
the most frequently travelled by the olive ridley,
we can focus our conservation efforts a lot better.
In the long term, I really hope that I can provide
information to the policy makers
that are trying to establish marine protected areas in the Pacific.
Well, it's really great to be this close to an animal,
especially one that's been tagged and will be feeding back
an incredible amount of valuable information,
which will help conserve a species
which is now very vulnerable to extinction.
Before we let the female go,
Christine takes a blood and tissue sample
which should later tell her what the turtle has been eating
and where it has been feeding.
With an identification tag on her flipper, she's ready to go.
OK?
As one of the smallest sea turtles,
olive ridleys are also one of the speediest on land.
But like all species, she can only breathe when still.
It is very humbling, I think.
This animal actually permits you to be with it for just a brief time
before she goes off into the ocean and does her thing again.
And I don't think there's anything better than that.
It's remarkable to see this ultramodern technology
on such an ancient creature.
Absolutely incredible.
Water's coming.
Yay! Yes, baby, come on.
Woo!
Christine names the turtle Margarita.
The next time we see her will be on a computer map,
when we can analyse where she's travelling.
In our turtle hatchery, we want to monitor more than one nest.
So, over a few nights,
we collect eggs from four other nesting females.
So now we have five nests.
All have sensors to detect temperature and movement,
and one has the infrared nest camera.
A day later, Christine checks
on whether she has a signal from Margarita.
I've just got the first data from the first 24 hours in.
And you can see where we started with her,
we were about here with her on the beach.
And then a few hours later we got the first ping,
already a few kilometres off the coast.
The next data that will come in will probably give me a better idea of
if she's starting her post-nesting migration or not.
And then hopefully within the next weeks,
we will really be able to follow the route that she's taking.
Previous studies have revealed that olive ridleys from Costa Rica
can travel 4,000km out into the open ocean in search of food.
They swim as far north as Mexico and as far south as Peru.
I just hope that I will get a year worth of data.
Christine's vital information about where Margarita and her other
satellite-tagged females are going to feed may later help to establish
more marine protected areas in the eastern Pacific.
Whilst Christine's investigating where the females go,
Vanessa is also looking at what they do under the water
while they wait to come ashore.
In the days leading up to the arribada,
she deploys a camera, dubbed turtle-cam.
I'm now on the way to recapture the camera
and have a look at the footage.
I'm super excited.
Turtle-cam is designed to release from the turtle shell
after a couple of hours,
but could have drifted several kilometres by now.
Vanessa must locate it using a VHF radio receiver
before it goes out of range.
Whoo!
We found it! SHE LAUGHS
It was far away, but we found it! Woohoo!
Back on dry land, Vanessa will now get a rare glimpse
of how an olive ridley behaves under the water.
This is good for my studies
to get a better understanding of just what percentage of turtles
I'm seeing with the drone that are actually at the surface.
So, when we've released the turtle,
I can see that she's very anxious to get back in the water.
She swims very quickly and goes to rest at the bottom immediately.
Sea turtles are air-breathing reptiles,
so hold their breath underwater.
It's almost four minutes before this one
comes up for air.
You can see her surface quite a bit, breathe, rest at the surface.
She goes through that pattern a little bit.
And we see her
in one moment swim through a school of fish.
The water's very turbulent, it gets very dark
and green as she's diving.
And I can tell that even her visibility is difficult,
because she's
almost bumping into some of the rocks
that are at the bottom.
And then she comes back up to surface and breathe a few times,
and then she'll dive again.
The turtle settles into a pattern of longer dives,
ranging from 7 to 28 minutes at a time.
But it's how long she spends at the surface that is most revealing.
The longest she's up top is just 1 minute and 40 seconds.
When she surfaces, she does hang out there for a little bit,
but it's relatively shorter than I anticipated.
Being on the boat, I was always under the impression
that they're kind of hanging out up there for hours,
but really it's not that long at all.
If the turtles are spending significantly longer
diving to the bottom than staying at the top,
this suggests what Vanessa is seeing from the drone
is just the tip of the arribada iceberg.
There could be thousands more waiting under the water.
It's the first time that we've ever got to see what a turtle is doing
in the days before a mass nesting event.
It's a great first start. I can't believe it worked,
I'm really excited to see it.
Despite the large numbers of olive ridleys that appear
in these mass nesting events,
the global population is now classified
as vulnerable to extinction.
The species has declined by around 50% in the past 60 years.
But the olive ridley is faring a little better than others.
Green turtles like this one
are one of the largest, and the only vegetarian.
They're now classified as endangered.
The hawksbill, identified by its
sharp, pointed bill for targeting reef prey,
is now critically so.
The threats facing sea turtles have never been greater.
Rising global temperatures and the escalation of plastic in our oceans
are among the modern dangers facing these ancient mariners.
Sea turtles have survived climate changes
that have occurred throughout their history.
However, something that sea turtles have not seen
across those many millions of years is humans.
Human activities have caused a tremendous impact
on nesting populations around the world.
Most of what we currently know about the biology of sea turtles and their
nesting behaviours is from research on loggerhead and green turtles,
which, like other species, come ashore to nest alone.
The olive ridley, which nests both alone and in arribadas,
remains more of a mystery.
The third stage of the mass nesting event
is the development of the embryos - the incubation.
This is the most fragile part of the turtle's nesting story.
The arrival of what can be hundreds of thousands
of nesting olive ridleys month after month
causes unexpected consequences
for the millions of eggs laid on Ostional beach.
As you see here, there are lots of eggshells all over the beach.
This is one of the problems,
because the number of turtles that come to lay eggs here
is so large that when they are digging their own nest,
they're going to be destroying
whatever nests are already in the sand.
The decomposing eggs are a feeding ground for bacteria and fungi.
Excessive levels of these microbes contaminate the sand,
reducing the oxygen the embryos need to survive.
Because of the number of nests that are laid on this beach,
you would think that the production of hatchlings from this beach
would be very, very high
but because of this problem of microbial load,
the actual hatching success
of the nests that are laid in this part of the beach
under natural conditions is actually 8% or less.
It's very, very low.
That means a staggering 92% of the eggs laid here
are likely to perish during incubation.
Predators also pose a serious threat.
Black vultures flock around nests
exposed either by the retreating tide
or dug up by dogs.
We've given our baby turtles the best possible chance of survival
to be able to observe them
during the critical stages of incubation and hatching.
So the walls of the hatchery will fend off the predators
and we washed the sand to reduce the life-threatening microbes.
In this hatchery, the hatching rate is probably around 80 to 90%
because the sand is very clean, it doesn't have the microbes,
so the embryos can develop properly.
It's a big, big difference.
However, we're not the only people to collect eggs on this beach.
During the first couple of mornings of an arribada,
the villagers of Ostional
are allowed to harvest olive ridley eggs.
Turtle eggs are considered an edible delicacy in many countries,
including Costa Rica.
The government allow it because of
the problems of the high nesting density and low hatching rates.
For almost 30 years,
the Ostional egg harvest has been one of the few legal extractions
of turtle eggs in the world.
The harvest is strictly controlled,
but, given the vulnerable status of olive ridleys, it is controversial.
We know that if you protect beaches around the world
from illegal poaching, sea turtle populations tend to do better.
But I think this is a very special case
because of the numbers of clutches involved.
It may help decreasing the amount of microbes
in the incubation environment.
In return for the financial benefit of the legal harvest,
the community helps to protect the nests that remain.
And when the baby turtles emerge,
villagers patrol the beaches to ensure
the tiny hatchlings make it safely to the ocean.
It's been six weeks since we put a satellite transmitter
onto our olive ridley turtle called Margarita,
and I've been tracking her post-nesting migration
on my smartphone.
Well, I'm now looking at where Margarita is
and I can see exactly where her journey continues
as she heads out into the open ocean.
The data reveals that, after leaving Ostional,
Margarita travelled northwest.
The last GPS location puts her in open water
between southern Mexico and Guatemala.
Other females tagged on Costa Rica's northern beaches
in Christine Figgener's research
have also mostly headed northwest on their journeys to feed.
One travelled nearly 3,000km west.
Christine's study is starting to show
a high density of olive ridleys feeding
in the waters off Mexico and Guatemala.
This data could inform greater protection
of this area of the ocean.
It's now at the start of Costa Rica's hot dry season.
On Ostional beach, temperatures can reach 36 degrees.
Last month, we relocated five olive ridley turtle nests
into a protective hatchery.
They all include a sensor to monitor temperature and movement
and one has cameras so we can watch the moment the eggs hatch.
To shelter our eggs, a shade cloth is helping
to limit the impact of the blistering summer heat.
We expect them to take between 45 and 50 days to incubate.
It's now day 40.
The turtle sensor has been taking
daily temperature and movement readings
and Roldan is now keen to get a visual on the eggs.
There's a little bit of condensation on the glass,
but the eggs look very nice, everything looks the way it should.
I don't see any signs of embryo death or anything like that.
The eggs look pretty healthy
so I assume that everything is proceeding normally.
What I'm going to do now is I'm going to look at
the incubation temperature.
In the dry season, nest temperatures above 35 degrees
kill most of the embryos incubating out on the main beach.
Temperature has varied from about 27 to 33 Celsius.
The narrow range of temperatures that I see here
is probably due to the shading that we place on top of the nest.
This is positive news.
Between 27 and 33 Celsius
is the ideal incubation temperature for olive ridleys.
But there are a couple of anomalies in the data.
I do see day 28, 29 a significant drop in temperature.
Just below 25 Celsius.
Likely due to a rainstorm that we had that day,
but the day after, temperatures went back up.
At times we have reached 35 Celsius,
which is the lethal range for this species.
But it drops to about 32, 33 Celsius.
That means that the clutch of eggs
is being developed at a pretty good pace.
The gender of the embryos is also determined by temperature during
the middle third of incubation.
Ours is above 30 degrees, indicating our nest will be mostly female.
Roldan will also need to check on any movement from the baby turtles
but at day 40 it's still a little early to expect to see anything.
Using the temperature readings, Roldan now predicts that the turtles
will emerge onto the beach around day 46 and 47.
So, hatching inside the nest should be less than a week away.
Everything looks good.
I'm very excited and hopeful that these things
are going to hatch as they should.
When laid, a turtle embryo is 1mm in diameter.
The eyes, tail, then flippers develop,
and it also becomes male or female.
The carapace, or shell, and scales form during the final phase.
The embryo will almost fill the 4cm egg before hatching begins.
Ours should now look something like this.
Whilst we don't expect to see anything more on the nest camera
until the moment of hatching,
there is another way to find out what's going on.
Joining our scientific team for this part of the incubation
is American researcher Lindsay McKenna.
Turtles lack vocal cords and ears, so scientists only like Lindsay
have only recently discovered these reptiles can make and hear sounds.
The first time I heard a vocalisation,
I was extremely excited because
it's a long period of time of just waves and background noise,
and then all of a sudden you hear a little squeak
or a little sound, and it's the most exciting thing.
Lindsay is the first scientist to ever record the sound
of olive ridley hatchlings vocalising inside the nest.
To hear what's happening inside our nests,
Lindsay uses holes in a second access box
to position her microphone as close to the eggs as possible.
Might take about a half hour to record each one
and then I do it about four times a day.
The first sound Lindsay hopes to hear
comes from the embryos inside the eggs.
If she hears it,
it may mean the turtle eggs are talking to each other.
It's a lower, longer vocalisation that, in my other study,
I only heard in the egg.
So, I didn't hear it when they were hatching
or when they were actually out of the egg.
And if this wasn't intriguing enough,
it should also indicate when the eggs will start to hatch.
So, last time it was hours from when
I heard the sound to when they hatched.
So, it's very exciting.
Three days later, and Lindsay has some results.
Hi, Lindsay. Hi, George.
What have you got for me? Would you like to have a listen?
Yes, please. I certainly would. Ready? OK.
SOFT COOING SOUND
Oh!
Again. Again?
SOFT COOING SOUND A little "ooh".
Mm-hm. Is that it? Yes. Wow, that's really clear. Very clear.
That sound is coming from inside an egg.
Correct. Now, how do you know it's coming from inside an egg?
There's only eggs in the nest and no sign of hatching yet.
OK, so that little noise is being produced by a single individual
hatchling before it comes out of the egg.
Correct. Why?
So, the study's still in early stages
but one reason could be that it's to signal synchronised hatching,
cos there's a benefit to hatching at the same time,
which is that it lowers the energy requirement for the hatchlings
to get out of the nest.
Do others reply or is a just one sound?
So, when I hear a sound like that or any chirp sound,
there is no response right away.
So, plenty of time will go by and then maybe I'll hear another sound.
So, if you're hearing this now,
it could be any time now that they'll emerge?
Yeah. So, our eggs could hatch any time now.
That's very exciting, Lindsay.
So, now it's a waiting game
and we'll keep a very close eye on the nest camera.
But while our eggs are relatively safe in the hatchery,
elsewhere in Costa Rica, and indeed around the world,
turtle eggs are vulnerable to poaching.
On some Central American beaches,
poachers destroy more than 90% of turtle nests.
Globally, illegal poaching has devastating effects
on local turtle populations,
but it's hard to police.
To try and change that, biologist Helen Pheasey
is undertaking a pioneering investigation
to uncover the poachers' trafficking routes.
We know that the eggs are leaving the beach.
We know that they are ending up in markets
and in bars and in restaurants.
We know that they're being sold door-to-door.
The problem that we have
is that we don't know what's going on in between.
To find out more, Helen is deploying innovative technology
into turtle nests.
This is a 3-D printed fake turtle egg.
It's the same shape, size, weight, as a green turtle egg.
It has a dimple that makes it look even more authentic.
Inside there is actually a GPS GSM tracking device and two batteries,
which will give us about six days of power.
When the poachers take the eggs,
they will also take the tracking device with them.
What we're looking to do is identify trade routes,
possible transport hubs,
possible key times in the season or maybe even in a week,
where we see a lot of activity going to the same place.
That would then enable us to inform law enforcement officials,
who are under-resourced.
Helen planted her first fake egg
on a beach on Costa Rica's Caribbean coast.
We were expecting it to go to the nearest town.
But then from that town, it then moved further north,
and that took us to somewhere new. We weren't expecting that.
They came up this road.
But the final point that we actually got a signal from this egg
was from a riverbed.
You can imagine the kind of frustration
of somebody buying this illegal egg
and thinking they're going to have an egg for dinner,
and then realising that they can't eat this,
and, you know, furiously throwing it into the river!
It's a pretty nifty piece of kit. I'm privileged to be able to use it.
Helen plans to plant more tracking eggs as her investigations continue.
Basically, at the end of the day, knowledge is power.
2017 was a breakthrough year for our understanding of
the new and growing threats facing life in our oceans.
Plastic pollution causes injury and death to thousands of sea turtles,
either caught in fishing nets, or by mistaking it for food.
Some studies reveal that over 50% of sea turtles have ingested plastic.
ROLDAN: The presence of plastics in the marine environment
is very impactful in ways that sea turtles have never seen before.
That's likely to only get worse in the next few decades.
A recent report estimates that there are more than 150 million tonnes
of plastic in our oceans.
And by 2025 that could reach 250 million.
How sea turtles are going to respond to that
is something that we have yet to see.
We are also starting to see how rising sea and air temperatures
may fuel more intense extreme weather events.
In September 2017, when Hurricane Irma hit the Caribbean and Florida,
it was one of the most powerful Atlantic storms ever recorded.
It affected over 6 million people,
but it also destroyed thousands of turtle nests on Florida's beaches.
We are talking about impacting heavily the largest assemblage
of loggerhead nesting sea turtles in the Atlantic.
We're talking about recovering populations
of green turtles in Florida.
We're talking about leatherbacks that nest in Florida.
All these sea turtle populations are going to be impacted.
A month later, Costa Rica was hit by Hurricane Nate.
Many olive ridley nests on Ostional were washed away
and October's arribada was two weeks late.
It may be a direct cause or just coincidence
but it is something that I have seen before.
I have seen heavy rains
completely changing the behaviour of the arribadas.
And so it's possible that a hurricane
could really stop these animals from reproducing.
Sea turtles have survived large scale climate changes
over millennia.
Their ancestors outlived the dinosaurs, after all.
But how fast they can adapt to the current changes remains to be seen.
The fourth stage of the nesting event is fast approaching -
the hatching - when we'll finally see
how and when our turtles push out of their eggs.
This is exciting. We're very close now.
It's nerve-racking. I feel like an expectant father
and the hatchery is my waiting room.
Inside the nest with the camera are 104 eggs.
It's day 44, and Roldan's eyes
have been glued to the downloaded footage from the nest camera.
It seems the eggs are now starting to move inside the nest.
Let me show you something, George.
Just look at this egg for a second. Mm-hm.
You see? Wow! You see what's happening? Yeah!
Something is wiggling. Something's alive. Oh, yes.
There's a split in the egg and the...
The head is sort of protruding.
See how it's... Oh! Look at that! ..squeezing itself out?
So, I'm actually looking at a turtle head
just pushing out of that eggshell.
That is correct. Wow.
The way they break through the shell is they have an egg tooth
that they use to kind of bite,
to pinch the shell and tear it.
Do you see it? The head came out this way, and the flipper,
the right flipper, went out this way.
So that is the head
sort of peeking out the window
and the flipper going that way. Wow!
Look at that. Fantastic. Absolutely fantastic.
It is the first time we've seen that.
Great shot.
And that seems bizarre,
you've worked on these animals for a long time...
That's right. ..and even you haven't seen this.
That's right. I just never had a camera inside the nest.
Let me show you another view of the nest.
So, here, what I want you to look at
is all the movement that's going to happen here.
Look at that.
Oh yeah! There's one, two.
You see that?
Is that two eggs going?
That's two. There's another one. Another one. Three, four!
I feel like a proud father now!
These are your babies. Yeah.
Now, one nice thing that we see
is that most of the movement is coming
from the bottom of the clutch.
I was not expecting that.
What I expected to see was movement everywhere,
not just concentrated in one section of the clutch.
The movement that seemed to start at the bottom
appears to stimulate others to move elsewhere in the nest.
And there's more going on than just what we can see.
Lindsay's microphone is now picking up more sound from inside the nest.
And it's exactly as she expected.
Now the eggs are hatching,
the long, low sound they made before has disappeared.
Lindsay can still hear higher pitched chirps
that, for the very first time,
can also be matched to our video feed.
HIGH PITCHED CHIRP
Our cameras show the faint chirp
is then followed by a synchronised movement a few seconds after.
Over a 30-minute recording, we hear and see it happen several times.
This means that the hatchlings may actually be signalling
that it's time to move together.
They're not vocalising very frequently, very often.
CHIRP
But other reptiles do communicate.
If it is communication, it's more of a signal.
They hear that and then they begin.
The delay may be due to the time it takes
for the hatchlings we see on the outer edge
to respond to a signal from others in the centre of the nest.
It's extremely exciting to have heard anything
and knowing that turtles do vocalise,
now we can look further into
what might the purpose of these vocalisations be.
CHIRP
I've got a feeling you've got something else up your sleeve.
Yeah, let me show you this other clip.
Look at the bottom,
this area, the activity that is going to happen here.
That is an entire...
Half the hatchlings now is outside the egg.
So it's the head here and the flipper down here.
That is a fully formed baby turtle. Head, carapace, flipper, this is it.
This is the very instant of its birth.
Wow.
And that hatchling is going to have to work its way
up through all those eggs?
That's right. All of them are going to have to climb to the top.
Each one of those that we're seeing here moving
is going to do exactly the same thing -
slowly come out of the egg and then slowly climb to the top of the pile.
Recent studies in other sea turtle species
suggest that slower developing embryos
may in fact be able to speed up their heart and metabolic rates
to catch up with their more developed siblings
to coordinate their escape and increase their chances of survival
against the awaiting predators.
What's that?
Fluid? Yes. That one crack...
That's what happens. Every time one of these eggs ruptures,
they lose volume,
because some of the fluid that is still inside the egg comes out,
and that makes the entire clutch compress towards the bottom.
As this is happening,
the air pocket starts to form. At the top.
And that space is going to be vital for all the hatchlings
so they can start working as a team to come up to the surface.
Wow.
Over the next three hours, the nest camera also reveals
that the hatching eggs alternate bursts of
frantic activity with periods of rest.
Sometimes up to 45 minutes at a time.
I'm actually blown away that we are able to get these images at all.
It's worked fantastically well.
We can see intricacies of the behaviour
that we never thought we would see.
And then I catch a glimpse of how
the hatchlings feed inside and outside the egg.
What's that little white blob there?
That is the yolk sac.
The yolk sac is very important because it holds the protein that
the hatchlings used
to fuel their metabolism,
so that they can climb to the top of the clutch and then dig their way up
to the surface of the nest.
The tiny hatchling will absorb the rest of the yolk sac,
which includes vitamins and minerals,
in through its abdomen to nourish it
for the first few days outside the nest.
So, the egg contained enough material to build a young turtle,
That's right. Because during those days,
these hatchlings are not going to be feeding.
They are just going to be living off that protein.
Over the next six hours
and into day 45,
the nest begins to change dramatically
as the rest of the eggs hatch out.
What we're seeing here now is the egg shells appear to be compacted
a little more towards the bottom of the nest.
It looks like there is scattered sand all over the place.
Oh! There is...
Oh!
Oh! There is a generalised movement.
So the sand I was looking at is not sand. It's hatchlings.
And as they move, they sort of reveal themselves.
That's pretty nifty.
I...I did not expect that.
What I see is there is some movement
then they stop, then there's some movement, they stop again.
So it's like touch-and-go for them throughout,
which is very interesting.
It's not a sustained movement.
Overnight, the nest camera reveals how the hatchlings move upwards.
You see that? Ooh!
Oh, yeah. That's not sand, that's actually hatchlings right there.
And look at that.
Wow.
See all the activity?
Oh, my goodness.
They are trying to climb on top of each other and, as they do that,
they hit the roof of the air pocket
and that's how the sand from the roof comes down.
And as the sand gets to the bottom,
they continue to get on top.
They seem to all move at the one time and then stop.
Yeah. So, it's definitely like a group effort.
Cos if it was just one doing it on its own, it wouldn't work.
They all have to be doing it at the same time.
That's right. And of course, as the sand falls down,
they can then move the sand below them, so they are basically...
Pushing it down. Pushing it up. Right, and they push themselves up.
It is incredible. That is...
Wow.
In time-lapse, the waves of synchronised movement
become even clearer.
We don't know if the hatchlings are triggering each other
by motion or by sound.
That's amazing.
It's a little pulse, isn't it?
Yes.
They move in pulses, exactly. There.
Over the next seven hours,
we discover that the hatchlings continue to pulse
on average every seven minutes,
gradually chipping away at the roof of the air pocket.
Now, you would never have predicted that...
No. ..without seeing it.
This is not how we envisaged the whole process.
I thought that once they came out of the shell,
that they were immediately going to start chipping away at the top.
But that's not quite what they do.
Instead, the hatchlings appear to elevate each other very gradually.
They're all reaching up.
And the one on top, they push one higher up...
Exactly. ..and eventually, the one on top eventually
hits the top of the... Exactly.
So, it almost seems accidental, how they do this.
But it works. It's very effective.
Eventually, they're going to reach the top.
There's movement, they take a rest, and they keep alternating.
So, this is just one nest.
Now, think about what the beach looks like with tens of thousands,
or hundreds of thousands of nests,
all those hatchlings are working at the same time towards
the surface of the beach. As you walk along that beach,
you would have absolutely no idea of all this frantic action
happening just under your feet.
Just under your feet, yeah.
That is the part that is amazing to me.
Discovering that the eggs do not hatch at the same time
has changed Roldan's understanding
of when and how the hatchlings begin to work together
to climb out of the nest.
I always thought that, from the get-go,
the whole group of hatchlings were going to behave as a unit.
But it's not a group effort
until they have all come out of their shells.
That, to me, is new and exciting.
It's something that I had not pictured,
that I had not imagined
and that I am really thrilled to see for the first time.
For the rest of day 46, the hatchlings persevere
in pushing the air pocket up through the sand.
So they're nearly at the top.
Oh! Oh!
The whole roof just came down on top of them. Fell down.
That's right. Yeah.
The collapse does not hurt the hatchlings.
This is really exciting.
This is the thing that really has me.
This whole chunk at the very top,
that is going to continue to slide down.
As that happens, they continue to move up towards the surface.
That's the cool part about this whole thing.
But as the sand continues to compact,
it obscures our view of the hatchlings.
Within 30 minutes, they all but disappear.
So, it's back to watching wildlife the traditional way
and we head out in the dark.
Hatchlings usually emerge at night
to avoid predators and high temperatures.
So we just have to sit
and we just have to keep our eyes fixed on this patch of sand.
That's right, until they finally make a move.
I have to get myself in a much more comfortable position.
Right.
We wait all night...
..but nothing happens.
Roldan decides to check again on the nest camera.
So, I am a little concerned about what is happening in the nest.
Looking at the video,
in the last several hours we haven't seen
any significant movement inside the nest.
The turtle sensor confirms this.
It also shows that the temperature inside the nest
has escalated in the last two days.
I see a couple of spikes that reach about 37 Celsius.
And that is above lethal temperature for these hatchlings.
So, I'm very concerned that the temperatures
are too high for them at this point
and that, along with the lack of movement, really worries me.
If the hatchlings don't emerge in the cooler hours tonight,
they will have to endure another day of potentially lethal temperatures.
Roldan must make a difficult decision whether to intervene.
So, I think that the proper thing to do is to dig them up
and...
..and just release them
because I'm afraid that they may not survive another day
of incubation at that high temperature.
In other species of sea turtles,
it can take 3-7 days from hatching to emergence.
Our olive ridleys are into their third day.
At this point, we don't know if the hatchlings are still alive.
Having put them into the hatchery,
their survival is our responsibility.
So, as dawn breaks, we attempt a rescue.
I feel very apprehensive.
Yeah.
OK. I see the first hatchling at the top.
Is it OK? It's...
..a little lethargic...
..but it's moving.
There it is. Oh, great.
There's another one.
The tiny hatchlings are just 6cm long.
Why are they so slow?
Well, it's going to take them some time to get adapted
to being outside the sand.
They've never seen daylight, or...
They don't know what air is like.
You have to be really careful with this.
Yeah. They're really small and easily injured, I imagine.
Yes, they are very delicate.
This is nerve-racking.
I didn't think it would be this nerve-racking.
Well, most of the hatchlings are about to come into my hands.
Oh, wow. Look at that.
Despite the lethal temperatures,
it seems that those at the top have survived.
Such relief.
Now, if I remember correctly, we put 104 eggs in here.
Yeah, so the question is how many of them hatched?
These look fine. Oh, wow.
There's a lot!
There's the... Oh, yeah, the...
..the probe. Yeah.
Could you add these? Yeah.
God, they're so tiny.
I have a few more to pull out.
That's easily 100.
It's good news. It was a productive nest.
Any more? There's one last one.
There is one that did not hatch.
I can smell something. That egg.
Yeah, right. So this is a dead egg.
You can see how discoloured it is.
The embryo died towards the beginning of the incubation period.
Think that's it? I'm down to the shells now.
What I'm going to do now
is make sure that there's nothing left to pull out.
Right. A straggler. Wow.
Looks like I got them all. Yeah.
Now I'm completely certain that everything is gone,
so what you see here is all the shells.
Yeah, and a few dead ones.
There's eight that did not produce a hatchling.
So, out of 104 eggs that went in, 96 hatchlings come out.
That's a very satisfying 92% success rate.
That's great. I'm so pleased.
Look at them go now. They're really...
Yeah, they're much, much more active.
They are experiencing a completely different environment
where there is a lot more oxygen.
That's why they look more lively now.
And they are starting to get ready to begin the race for life, I guess.
To escape all the predators that are in the water and on the beach.
We need to release the hatchlings quickly,
as the rising daytime temperature will overheat them.
This is now the final stage of the mass nesting event,
the journey to the ocean,
where the turtles will face a whole new set of challenges.
OK, George, what we're going to do
is we're going to tilt the boxes slowly, gently,
and we're going to allow the little hatchlings to crawl out.
This is such fun.
Look at them. Yeah.
And the race begins. The race begins!
The race for life.
Come on, guys.
Because we're releasing them in daylight,
we're going to stick with them
to protect them from the vultures and other predators.
Any more in there?
There's one little turtle left in my box.
Come on.
Yeah.
A bit of a slow one.
There you go. Last one coming out.
They are beautiful, aren't they?
I can't stop smiling.
It's one of those things, you just...
If you didn't smile when you saw this,
there'd be something wrong with you.
There's no confusion about which way to go, is there?
To find their way to the ocean,
the hatchlings look for the widest, brightest horizon,
and use the gentle slope of the beach to orientate towards it.
It looks like they have good energy.
And now they're really going for it.
Like their mothers, these hatchlings will imprint on the unique
magnetic signature of this beach to navigate back here as adults.
Scientists don't yet know exactly how they do this
but theories suggest it may happen inside the nest
or during this journey across the sand.
The fastest reach the surf safely,
but entering the ocean is the next challenge.
Because the hatchlings are so small,
the wave tends to push them back up the beach again.
Some enter the water very successfully, very quickly.
Others are pushed back several times.
That is a very exhausting process.
They have to spend a lot of energy doing that.
Now I can see just how vital
the yolk sac we saw so clearly inside the nest is
to fuel these tiny reptiles.
If the hatchlings can hit the approaching waves head-on,
the water's power can push them forward and away from the shore.
For the next 24 hours, they enter a phase known as a swimming frenzy,
as frantic flipper movements power them away
from the predator-rich coastal waters.
Offshore ocean currents will sweep them into deeper, safer water,
where they'll feed and hopefully mature to adulthood.
I can't tell you how relieved I am
that most of the eggs hatched successfully.
And now these tiny turtles are making their way
to a new life in the ocean.
Out there, survival is a lottery.
But if the female hatchlings hit the jackpot,
as adults they will return to this beach to lay their own eggs,
and that is quite remarkable.
With the hatchlings from the first nest showing no sign of heat stress,
Roldan decides to give the four remaining nests
more time to empty naturally.
The drop in temperature tonight
should trigger the start of a mass emergence.
Finally, two hours after sunset...
Oh!
I see movement.
So, this little crater that is forming here
shows me where exactly they are going to pop.
We are coming to that moment.
Whoa!
This is the beginning of the end.
Yep.
It's a head.
There it is, right there.
It's moving.
Come on.
It is pretty normal that you get one or two coming out
ahead of everybody else.
There's the head sticking out.
Soon there's going to be a flipper.
There's another one coming up right there.
My guess is that the rest will be sitting right underneath.
And another nest is starting to erupt.
Once the hatchlings start, there's no stopping them.
Finally, we can see that the hatchlings are alive.
It's definitely worthwhile.
They look very healthy
and very active.
They are just beautiful little turtles.
This is absolutely incredible.
These tiny turtles have just emerged from their underground nest,
and they have helped each other on the way up to the surface.
And now they're here, there'll be a little period of confusion,
a bit of orientation, until they work out which way the ocean is.
And then they'll go.
Our hatchlings have been able to develop in clean sand,
avoiding the danger of microbes on the main beach.
They have been protected from predators whilst inside the nest
and they have survived potentially lethal incubation temperatures
thanks to the shade cloth over the hatchery.
They are just driven by an innate desire to get to the ocean.
It's wonderful. Really wonderful.
The hatchlings from the two nests
make it to the ocean before midnight.
It takes another couple of days and nights
before everyone is on their way.
In the end, 424 baby turtles successfully emerged
from the five nests in the hatchery.
We put 485 eggs in, so that gives us a hatching success rate of 87%.
That's more than ten times the normal rate on the main beach.
Unfortunately, eggs incubating outside the hatchery
during the dry season
are unlikely to survive the lethal temperatures.
When the cooler season returns, hatching rates will improve.
Significantly so, if the females lay their eggs on less used,
and therefore less contaminated, sections of the beach.
Sometimes, this beach is capable of producing pulses of hatchlings.
Tens of thousands or hundreds of thousands of nests that are laid
in this healthier sand, then you can imagine
a pulse of very large numbers of hatchlings
that are going to make it into the ocean.
Despite the low hatching rates,
Roldan thinks that overall survival rates for olive ridley hatchlings
may be higher from this arribada beach
than from other beaches where turtles nest alone.
The impact of predation on that high number of hatchlings
tends to be lower
so those hatchlings are going to have a better chance of surviving
to a size that would escape most predation.
Safety in numbers might help these mass nesting olive ridleys,
but more must be done
to protect them out in our oceans.
For Roldan, this departure is the culmination of
a ground-breaking and revealing experiment.
The knowledge acquired here is going to help us gather more information
about this population
and understand how it might persist over time
or how it might be affected by a changing world.
This has been quite a voyage of discovery for me,
coming to Costa Rica
to witness the extraordinary world of the olive ridley turtle.
We've discovered that pheromones may help trigger
these mass nesting events
and learned that turtle embryos
could be telling each other when it's time to hatch.
For the very first time,
we've been able to witness the incredible moment
when hatchlings break out of their shells...
..and we've revealed how they work together in synchronised pulses
to move up and out of the nest.
Although we're right at the start of much of this ground-breaking
research, I'm astounded at how the rapid developments in technology
are revolutionising the way that scientists can study
these remarkable animals.
Knowing their initial challenges may enable us to better protect them
from some of the dangers they face in our ever-changing world.