Every month at Costa Rica’s Ostional National Wildlife Refuge, tens to hundreds of thousands of female sea turtles arrive, often within a few days of each other, to lay their eggs on the beach.

Ostional is one of the only places in the world where such large arribadas occur. It may have to do with sea currents, beach orientation, sand type, and the like. Such arribadas may also provide “strength in numbers” for females and their eggs, possibly maximising their chances for survival.

The biggest sea turtle arribada in Ostional happened in 1995 and numbered a whopping 500,000 turtles! The big one currently taking place in Ostional isn't likely to break that record, but we're still talking tonnes of turtles!