These tour islands (the Negritos make up two) are situated at both ends of the Gulf of Nicoya. They owe their origin to tectonic movements that led to the creation of this gulf. Guayabo Island is an important block of sedimentary rock some 50 m high in the shape of a rhomboid, and access to it is difficult from the pebble beach, which is the result of a former landslide. The rest of the surrounding area consists of cliffs jutting out into the sea.
The vegetation covering it consists of bushes and small plants scarcely over one metre high. Their importance lies in being the larges of the four known nesting areas for the brown pelican (Pelecanus occidentalis) in the country with a population of 200 to 300 birds. Besides the many sea birds, it is also a place where the peregrine falcon (Falco peregrinus) winters. Near guayabo, there is a sunken ship, which has enabled a small coral reef and a bank of mussels (Brachidontes puntarenensis) to establish themselves.
The Negritos Islands, consisting of basalts and breaches of the Nicoya complex, are covered in semideciduous forest. The predominant trees are frangipani (Plumeria rubra), spiny cedar (Bombacopsis quintanum), lacewood (Calycophyllum candidissimum) and gumbo-limbo (Bursera simaruba). In some parts, near the rocks, there are homogeneous patches of chira (Bromelia pinguin) and palm (Bactris guineensis). The yellow-naped parrot (amazona auropalliata) nests here. The waters surrounding these islands are very rich in marine fauna; some of the most common fish are the Pacific red snapper (Lutjanus peru), the spotted rose snapper (L. guttatus) and the yellow snapper (L. argentiventris).
The Isla de los Pájaros is more or less round dome-shaped. At low tide, it is possible to walk around it along the two small beaches and a narrow platform. The vegetation consists of a low forest with patches of grassland with charral shrub. The predominant species is wild guava (Psidium guineense)
These islands are in the Gulf of Nicoya. The distances form Puntarenas are as follows: Guayabo 8 km, Negritos 16.5 km and de los Pájaros 13 km. to visit them, a permit is needed from the Tempisque Conservation Area. In Puntarenas there are hotels, restaurants and markets and it is possible to hire boats.