Hundreds of female turtles gather in coastal waters and come simultaneously on a shore in a spectacular mass-nesting event called arribada ('arrival by the sea' in Spanish). Scientists cannot explain how these ladies communicate to get ashore all together, but this mystery is to be witnessed. Two major arribada sites in Costa Rica are Playa Ostional and Playa Nancite, on the Pacific shore. The nesting lasts around ten days, taking place in different months, peaking in September–October.
After two months, tiny baby turtles less than 4 cm long start getting out of the nests.