BBC: Nature's Turtle Nursery Inside the Nest

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.