The diminutive Green Turtle nests in huge numbers at Tortuguero from June to October.
From August to December Olive Ridley Turtles, the smallest of Costa Rica's five species of turtle, nest on the Pacific at Playa Ostional. Their arrivals are timed according to the moon, generally starting around a week before the new moon. During this period, typically on the darkest nights a few days before the new moon, arribadas or mass nestings can also occur, where thousands of Olive Ridley Turtles arrive at Playa Ostional to lay their eggs.
From October to March, Playa Grande on the Nicoya Peninsula receives the largest turtle, the Leatherback, although sightings have become extremely rare. The Leatherback has also been found nesting on the Caribbean coast at Tortuguero between mid-March and September. Hawksbills and Loggerheads have also been seen nesting at Tortuguero at this time.