Ostional Wildlife Reserve

Ostional Wildlife Reserve
The black-sand beach of Ostional

The beach of Ostional is the scenery for a rarely-seen biological wonder. In rainy season, the week before new moon, hundreds – and sometimes hundreds of thousand sea turtles come to one specific mile of beach at Ostional to dig their eggs into the black, volcanic sand.

The Ostional Wildlife Refuge in Costa Rica was created in 1984 to protect one of the world’s most important nesting sites of the olive ridley sea turtle.

Only olive-ridleys and their close relatives, Kemp’s Sea Turtles, the latter an Atlantic species synchronize their nesting in mass emergences or "arribadas", the Spanish word for arrivals. See also: » Sea turtles

Ostional sea turtle
Sea turtle swimming in the ocean

Some days or weeks before the mass nesting, the "flotilla", an increasing number of turtles, congregates close offshore. After some days, prompted by some secret signal, the "arribada" will begin. At first, a few hundred turtles will come out on the beach, followed by a steady stream of animals for the next three to seven days.

Olive Ridleys
Turtles arriving in Ostional

Turtles nest at Ostional year round, but peak time is during rainy season. From August through December arribadas occur regularly once, sometimes even twice a month, and the numbers of nesting females are in the range of hundreds of thousands as opposed to tens of thousands for the dry season months. Usually the arribadas occur during the darkest nights: a few days before the new moon, when the majority of turtles arrives between 8 pm and 4 am.

The largest "arribada" thus far recorded in Ostional, took place in November 1995 when a calculated 500 000 females came ashore.

The turtles generally ride in on the high tide at night but during an arribada they start arriving soon after sunset and keep coming until 6 am the next morning.

Turtle laying eggs
Turtle laying eggs into the sand

Used to a life in the ocean, the turtles painfully drag their heavy bodies over the beach until they get over the high tide line. There, flicking clouds of sand, they dig a nest with their flippers to deposit around 80 – 100 soft-shelled, white eggs, the size of a ping pong ball.

Over the course of a five-day arribada nesting turtles will leave up to 10 million eggs on the beach of Ostional.

Amazingly, Ostional is the only beach in the world where harvesting turtle eggs is legal. Scientists found out that most of the eggs deposed in the first nights of an arribada are destroyed by other turtles coming later to dig their nests.
Therefore, since 1987, the government of Costa Rica allows the community of Ostional to harvest the doomed eggs on the first three days of an arribada. In return, the villagers protect the turtles, clean debris from the beaches and patrol day and night for poachers.

Nest of Olive Ridleys
Small turtles hatch after around 50 days

The baby turtles hatch within 45-54 days depending on incubation temperatures, which will also determine if they will become male or female. They face varying degrees of success in each of the clutches that are laid in large groups to increase their success of surviving.

In general the baby turtles hatch at night, but it may also happen that you are sitting in the afternoon on the beach and suddenly, next to you the sand becomes live and small heads pop up.

Turtle hatchling

As soon as the hatchlings have struggled out of the sand, the race to the ocean begins. With eyes barely opened, the mini turtles smell the breeze and instantly know the right direction.

Women and children from the community of Ostional accompany the hatchlings as they clamber toward the sea, protecting them from dogs and vultures. The small turtles may not be carried all the way to the ocean as they need the run across the beach to develop their lungs. You can carry them a piece of way over the hottest stretch of sand and let them run the rest, while keeping the vultures away.


Having reached the ocean, the mini turtles still aren’t safe – the next cast of predators awaits them under water.

Most hatchlings don’t reach the age of maturity which will take 10 – 15 years. But those who make it will remember their home beach.

Sea Turtle in Ostional
Olive ridley sea turtle in Ostional

Adventurous turtles may paddle across the Pacific ocean as far as India but their impressive natural navigation system steers them back to their place of birth in Ostional where they will lay their eggs again into the black sanded beach, like their mother once did.

Visiting Ostional:

The Ostional Wildlife Reserve extends 15 km along the shoreline, including the beaches of Ostional, Nosara and Guiones. It is only a narrow, 200 m wide strand of beach, but extends inland along the estuaries of the rivers and mangrove swamps where it also protects large colonies of birds. Offshore the reserve incorporates another 3 miles stretch of maritime zone.

Vultures on the beach of Ostional
Vultures preying on turtle eggs in Ostional

During nesting season (Aug – Nov) solitary turtles arrive almost every night at Ostional and sometimes the rare and endangered giant leatherback turtles and green sea turtles come to nest as well.
On a daytime walk on the beach you see lots of white shreds from broken turtle eggs. Crowds of black vultures sit in wait for hatching turtles or they pick and scratch impatiently with their beaks and feet in the sand to uncover the tasty eggs.

At night, when there is an arribada, you must check in with the ranger booth at the southern end of Ostional where you pay the entrance fee of $ 10. No flashlights or flash photography is permitted.

Arribadas usually occur during the darkest nights: a few days before the new moon. The majority of turtles arrives between 8 pm and 4 am.

Mass tourism disturbs turtles in Ostional

Ostional Tourists
Ostional in September 2015

In September 2015 the number of tourists in Ostional reached a peak as tour companies hauled buses full of people to the turtle nesting site. Though there are regulations about visiting Ostional during an arribada, visitors often ignore the rules and enter the beach without the required guide and through unauthorized access points.

Humans on the beach disturb the turtles and keep them from laying their eggs. If you visit Ostional with an organized tour, insist that the operator acts responsible.