Sizes:
Guayabo: 6,8 hectares
Negritos: 80 hectares
Los Pajaros: 3,8 hectares
Distance from San José: 118 via road and boat
Dry season: January through March

Access to these reserves is very restricted, and requires chartering a boat.
These four islands (Negritos are two) are located at both ends of Nicoya Gulf, one of the most beautiful scenic regions in the country. The objectives of making them biological reserves were to preserve numerous populations of sea birds conserve their plant and wildlife, and guarantee that so much natural beauty could be enjoyed by all Costa Ricans forever.

Guayabo Island is a rocky mound that stands about 50 meters high. It has a rhomboid shape and a difficult access by means of its one single beach, which is small and pebbly, the result of an ancient landslide. The rest of the island is made up of cliffs against which the sea hurls itself in constant battle. The result is the formation, mainly on the northwest side, of several medium-sized caves, which can be seen at low tide.

The plant life that covers the rock is composed of a small number of thorn bushes, shrubs and small plants which grow about 1 meter high. The shrubs include the Guaco, where the birds nest. Wildlife is almost exclusively represented by birds. At a certain time of the year migratory sea birds come to these islands. Guayabo is exceptionally important for the protection of birdlife for two reasons: with a population of 200-300 individuals, it is the largest of the four nesting colonies of brown pelican that have been found in Costa Rica and it is the wintering site of the peregrine falcon. Other wildlife species are the ctenosaur, fiddler crabs and Sally lightfoot crabs.

Negritos Islands are covered with a semi-deciduous forest in which the predominant species are the frangipani and gumbo-limbo. These birds use one of the islands as a bedroom. The waters around the islands are filled with giant conch and oysters, and there are abundant tripletail, dolphin, and mackerel.

Pajaros Island is almost round and dome-shaped. Use a boat to surround the island to observe the rocks of the intertidal zone which are completely covered with mollusks called rock oysters and crustaceans called barnacles. The plant life is composed of a low-growing forest and of patches of second growth grass. The predominant species is the wild guava.

There are no visitor facilities.

Animals found here: ctenosaur, raccoon, parrots, white-tipped dove, red land crabs and the land hermit crabs.

Common fish seen here: Pacific red snapper, spotted rose snapper, yellow snapper

Birds found here: brown pelican, magnificent frigatebird, laughing gull, yellow-naped parrot, and brown booby.