Ecology and removal of introduced rhesus monkeys: Desecheo Island National Wildlife Refuge, Puerto Rico.

A field project was conducted to remove an introduced population of rhesus macaques (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. The present removal project began in 1985 and continued through 1987. During this period, 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 has been extremely difficult to determine due to the rugged terrain and the furtiveness of the monkeys. The population did increase since introduction and was composed of apparently healthy individuals, generally in excellent physical condition. The population was well adapted to the harsh environment of Desecheo Island. No permanent sources of fresh water exist on the island and feeding adaptations focused on consumption of the wood pulp of the almacigo tree (Bursera simaruba) as a result. Huge amounts of this wood pulp were consumed daily for both nutrition and as a source of moisture. Cactus and other plant species were utilized as secondary sources of moisture and nutrition, including lesser amounts of almacigo fruit and leaves. Circumstantial evidence indicates the monkeys are egg predators. Social adaptations involved dispersal into small groups to optimize foraging conditions.