These Biological Reserves are located in the Nicoya Gulf at Guanacaste province and the three of them serve as habitat and reproduction of abundant populations of marine birds, as well as species of flora characteristic of the zone. Guayabo Island is an important rock of 50 meters of height, cover in some sectors by shrubs and small thorny plants. On the other hand, in Negritos Islands there is few vegetation basicly small plants. In Pajaros Island, the vegetation is constituted by a forest of little height and patches of grass. The fauna of the three islands is represented mainly by marine birds. Some times of the year migratory marine birds arrive here to look for food and to reproduce. The most characteristic species are the tijereta of sea, the laughing gull and the brown pelican. This last one uses Guayabo Island as nesting area and calculates that a population of 200 to 300 individuals. Other species of present fauna in these islands are the travelling hawk, the white-tail dove and garrobo, violinst crabs, marine crabs, cambutes, clams and great variety of fish.