With the advent of drones, we have unprecedented access to wildlife phenomena that we wouldn’t normally see. This privilege is highlighted in new footage of what may be the largest swarm of sea turtles ever caught on camera, and it’s breathtaking.

Every year, hundreds of thousands of female sea turtles make their way to Costa Rica’s Ostional National Wildlife Refuge to lay their eggs on the beach. Established in 1983 as a protected area specifically for the turtles, it’s thought the refuge is home to the second-largest gathering of turtles in the world. Only Mexico’s Oaxaca has more during egg-laying season.

This particular swarm of sea turtles, mostly olive ridleys, accumulating out at sea was filmed by biologist Vanessa Bézy back in November 2016. Bézy, who has studied these mass arrivals – known as arribadas – for years, quickly realized she had caught something special on camera.

“I immediately knew there was something special going on,” Bézy told National Geographic. “To this day I’m still blown away by the video. They look like bumper cars out there.”

She has released the footage now, to highlight the threat of tourism to this crucial turtle refuge. There are currently protections in place that prevent development encroaching on the nesting site, as well as responsible tourism that allows people to watch the incredible site of nesting turtles and hatchlings making their journey to the sea, but Bézy says due to the speed and growth of developments in and around Ostional, more regulations need to be put in place to ensure the safety of this population.

According to the video, on the day the footage was filmed there was the equivalent of 5,000 turtles in an area the size of a football field, covering a total area of more than 1,000 football fields, at a density of roughly one turtle for every square meter. Because turtles can be seen rising to the surface it’s thought even more turtles were present unseen beneath the waves.

It’s not known why so many turtles gather here for nesting, or even how they know to return to the beach where they were born. One suggestion is they use the Earth’s magnetic field as a guide. This particular beach in Costa Rica may be orientated advantageously towards sea currents, or have a particular kind of sand preferred by turtles.

It’s still unclear too why the turtles gather in such quantities. Strength in numbers is a possibility, as hatchling survival rate is famously low. For olive ridleys – the second smallest sea turtle – which lay around 100 eggs, and gather in numbers of up to 10,000 to nest, just 0.2 percent of eggs will survive to hatch, and only 1 percent of those will survive to adulthood.

Arribadas last for five nights usually, and the incubation period for the eggs is around 45 days and the whole thing occurs between August and October each year like clockwork, so for tourists, it’s often a top destination on their travels. Hotel developers are capitalizing on that, and settlements are growing quickly in the region. Bézy hopes that by releasing the footage it will spotlight how unique the region is and that it needs to be protected, now more than ever.   

[H/T: National Geographic]