About Arribadas

What is it and why is it so special?

What is an arribada?

An arribada (Spanish word for arrival) is a synchronized mass-nesting event of sea turtles.


Hundreds and sometimes thousands of sea turtles simultaneously come ashore to lay their eggs on a small stretch of beach within a matter of days. 


This behavior occurs in the Ridley genus (olive ridley and Kemp’s ridley turtles) and at few sites across the globe. The discrete start of events, small geographic scale, and short-period of time in which they occur make it a unique natural phenomenon.

How and why do arribadas exist?

We do not know how or why this behavior exists.


Of many possibilities, scientists believe the timing of nesting may be a response to a chemical smell (or pheromone) secreted by a gland and the behavior may be a “safety in numbers” strategy that increases the survival of hatchlings.

Where and when do they occur?

Arribadas occur at few sites across the globe, with varying frequency and size. At many sites, arribada sea turtle populations are rapidly declining as a result of a long history of overharvesting.

Arribadas occur at Ostional Beach in the Ostional National Wildlife Refuge almost every month of the year. The largest arribadas occur in the rainy season (July - November), when hundreds of thousands of turtles nest over a period of 3 – 4 days. In the dry season (December - June), smaller events typically consist of tens of thousands of turtles nesting over 2 - 3 days. 

Central America




At Ostional, the largest arribadas occur in the months of September and October, when up to 500,000 turtles nest at once.









Average number of turtles per event


Declining or

Data Unavailable




Number of events per year


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         +506 8351-4000

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         Playa Guiones, Nosara 

         Ostional National Wildlife Refuge

         Guanacaste, Costa Rica

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