Desecheo Island, Puerto Rico

Desecheo is a small, mountainous, uninhabited island belonging to Puerto Rico. It is located north of the Mona Passage 21 kilometers away from the western coast of the island (Punta Higüero) and 50 km northeast of Mona Island. Officially, it is part of the Mayagüez municipality.

Because Isla Desecheo has healthy reef life and clear waters, it is popular with divers; however, the island itself is closed to all visitors due to the presence of unexploded military shells. While uninhabited, the island was used by pirates in the 19th century and by the United States Marines in the Spanish-American War (1898). Although Desecheo was declared a wildlife reserve in 1912 (mainly to protect its large variety birds), other groups continued using the island, such as the U.S. Armed Forces as a bombing range (1942-52), the U.S. Air Force for survival training (1952-64), and the National Institute of Health (NIH) for animal experiments (1966-86, introducing rhesus monkeys for medical research), among others. Administration of the refuge was turned over in 1976 to the Department of Fish & Wildlife Services, and since then called the Desecheo National Wildlife Refuge, with the objective of restoring and protecting historic seabird colonies and natural island ecosystems. Nevertheless, seabird nesting has virtually disappeared from the island due to past military bombing, illegal hunting, fires, and the introduction of rats and nest-predating rhesus monkeys.

From 1985 to 1987 a field project was begun to remove the introduced population of rhesus monkeys (Macaca mulatta) from Desecheo Island National Wildlife Refuge, Puerto Rico. A group of 57 monkeys from Cayo Santiago was released on Desecheo Island in 1966 to study processes of adaptation. Observations in 1969 and 1970 implicated the monkeys in a drastic decline of the nesting populations of brown boobies (Sula leucogaster) and red-footed boobies (Sula sula). Previous efforts at trapping and removal had been conducted in 1977, 1979, and 1981. During 1985-87, field investigations were conducted regarding ecology and behavior, simultaneous with the removal of 66 monkeys from the island. Estimates of the monkey population size have been inaccurate. The total number present on the island was “extremely difficult to determine due to the rugged terrain and the furtiveness of the monkeys.” The population did increase and were found living on the island in excellent physical condition and well adapted to the harsh environment of Desecheo Island, although no permanent sources of fresh water exist on the island. The monkeys adapted by consuming huge amounts of the wood pulp of the almacigo tree (Bursera simaruba), cactus, and other plant species. Circumstantial evidence indicates the monkeys are egg predators.

In 1989, the bird list for Desecheo consisted of 52 species—including brown boobies, red-footed boobies, magnificent frigatebirds, American oystercatchers, laughing gulls, bridled terns, mangrove cuckoos, belted kingfisher, pearly-eyed thrashers, red-tailed hawks, herons, egrets, Caribbean martins, peregrine falcons, and various types of swallows—of which only 10 species were resident. Needless to say, these bird populations decreased greatly throughout the 20th century.

For more information, see

For bird species that have made Desecheo Island their permanent or temporary home in the past, see article from the Caribbean Journal of Science (Vol. 25, No. 1-2, 24-29, 1989) at

For more on rhesus monkey removal, see

Photo of Desecheo Island, seen from Rincón, Puerto Rico.

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