By Graham Duggan  

Sea turtles are solitary creatures, who spend most of their long lives swimming in the world’s oceans. That is, until they come together to nest.

In Turtle Beach, a documentary from The Nature of Things, cameraman Hugo Kitching waits (very) patiently in Ostional, Costa Rica, for olive ridley sea turtles to arrive en masse to nest — a phenomenon known as the arribada.

At certain times of the year, tens of thousands of these turtles gather along the coast, haul themselves up the beach and deposit their eggs. It’s thought that this synchronized arrival is, in part, a numbers game: the more eggs in one place, the better their chance at survival, as predators are overwhelmed by the sheer number of nests.

After each female has dug her nest in the sand and deposited around 100 eggs, she returns to the sea, her job done. But for the millions of eggs that are now incubating under the sand, the journey is just beginning.

Inside the nest

They may be loners as adults, but olive ridley turtles begin life as part of a team. Nestled in the sand 40cm below the surface, the eggs incubate for about seven to eight weeks until they are ready to hatch. And then they begin to vocalize to let their siblings know about it.

Lindsay McKenna, a researcher featured in Turtle Beach, studied sea turtle nests and the sounds that baby turtles produce before and after hatching. “The first time I heard a vocalization, I was extremely excited. All of a sudden, you hear a little squeak or a little sound.”

The fact that the turtles are making sounds at all is impressive — turtles lack vocal cords, so scientists assumed for a long time that they were completely silent. But a few years ago, it was discovered that turtles actually vocalize while inside the nest, and McKenna’s observations have added to this surprising research.

To pick up vocalizations, McKenna placed a microphone inside a study nest and recorded what she heard. But even before any signs of hatching, she recorded sounds coming from inside the eggs. “It’s a longer, lower vocalization that I only heard in the egg. I didn’t hear it when they were hatching or when they were out of the egg,” she says.

The baby turtles appeared to be communicating with each other while still inside their shells. “Whenever I’d hear it, it was hours to a day before hatching,” McKenna says.

Timing and teamwork

Because temperatures throughout the nest may not be equal, some turtle embryos develop a little slower than others. The calls from the more developed embryos could signal the slowpokes to speed up.

It’s been shown in other turtle species that less developed embryos can detect the heart rates of their more mature siblings and ramp up their own development to catch up. It’s possible that vocalizing in the sea turtle nest could be another signal that hatching is imminent.

The first hatchlings to break free of their shell have a head start in life, but they find themselves an impasse. They have broken free of their shells but are still trapped in the nest chamber under half a metre of sand.

Luckily, help is on the way — the movement of the first hatchlings triggers synchronized movement throughout the nest. Now, the early hatchlings just need to be patient.

Making a break for it

As the turtles begin to hatch, their vocalizations change from lower sounds to higher-pitched chirps, and the nest begins to fill with wriggling hatchlings. “One theory is that [this] could possibly be a signal to synchronize hatching because there are benefits if they all hatch at the same time,” says McKenna. “It actually requires less energy for them to get out of the nest.”

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Now, the teamwork begins. In Turtle Beach, researchers observe as, every few minutes, a vocalization goes out and, in unison, the hatchlings start climbing the sides of the nest chamber. They scrape away at the sand until the “ceiling” collapses on top of them.

They then dig themselves out, have a rest, and try again. Over several hours, they repeat the painstaking process — climb, dig out, rest, repeat. By joining the sound recordings to video filmed inside the nest, the experts are able to watch, and hear, exactly how it takes place.

Free and alone

Finally, after making its way up through the sand, the first hatchling’s head pokes out above the surface and breathes its first breath of fresh air. Another head follows, and then another, until the entire group claws their way out. They may be exhausted, but for these siblings, their teamwork has paid off.

The hatchlings can now navigate toward the shore. It’s thought that they gravitate toward the brightest horizon, usually the light of the moon reflecting off the ocean. Each of them are on their own as they try to avoid predators and pitfalls on their way to the water.

Those that make it to the ocean are lucky; they have successfully hatched, escaped their sandy nest, evaded the dangers that lay before them on the beach and gotten past the powerful waves on the shoreline. Now, they face the open ocean alone. The odds are not in their favour — only one in 1,000 will reach adulthood.

But one day, if their luck holds, they will reunite with some of their siblings on this beach, dig nests and lay the next generation in the same stretch of sand.

Watch Turtle Beach on The Nature of Things.

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