An arribada (mass synchronised sea turtle nesting) is a unique nesting phenomenon common to both the Olive ridley and the Kemp’s ridley sea turtle. The best place to witness an arribada is Ostional beach on the Nicoya Peninsula in Costa Rica. Arribadas at this beach are considered the largest in the world, with as many as a million sea turtle eggs laid in the beach nesting areas each year. Arribadas occur on a lunar cycle of approximately 28 days. The majority occur around the start of the last quarter moon; however, this event may take place at any time including the full moon, and two arribadas (first and last quarter) may occur in the same month. The size and duration of the arribadas varies between the dry and wet seasons. Those occurring in the dry season of January to April tend to be smaller (approximately 5,000 turtles) and of shorter duration (less than four days). In the wet season of May to December, up to 300,000 turtles may lay over a period of 8 to 10 days. On a number of occasions between August and October, two arribadas of 10 days each have occurred in the same month. This results in continuous activity during the month with a few days of lower activity and two peaks of maximum nesting.
Observing one of these mass synchronised nesting’s is a must for nature and wildlife enthusiasts. The best months to see the biggest arribadas are between July and December. If you would like to volunteer in Ostional Wildlife Refuge please contact Volunteer Latin America.