GRADUATE STUDENTS

Néstor Pérez

by Suzanna Engman

Doctoral candidate Néstor Pérez studies the endemic Mona Island rock iguana (Cyclura cornuta stejnegeri), which was first investigated in 1977. His research explores why there are so few iguanas on the island and why adolescent iguanas seem to have disappeared from the island’s population. Using radio telemetry and mark-and-recapture techniques to study their home range, nesting ecology, and demography, he teams up with Department of Natural and Environmental Resources (DNER) collaborators and University of Puerto Rico, Río Piedras students to accomplish his research goals.

Pérez has observed how much space each animal needs and how they interact with each other. He also was the first to observe and document the female iguana’s nesting migration to the few sandy areas available on Mona with optimal nesting conditions. The female lays an average of 14 eggs, and mortality during the egg stage is very low, only 11 percent. The highest rate of mortality in a single year coincided with heavy rains that flooded many nests. In the past, the island’s introduced pigs preyed on iguana eggs, but loss of eggs to pigs was reduced substantially when about 10 years ago, the DNER put up a fence to protect the main nesting sites. Another management measure started in 1999 by the DNER, the Headstart Program, consists of raising iguana hatchlings in captivity for up to 24 months, until they are large enough to escape being hunted by the island’s feral cats and other native predators. The efficiency of this program is being assessed by Pérez and DNER researchers.

Unlike other West Indian iguanas whose populations have declined dramatically because of habitat loss, Mona Island iguanas have not experienced dramatic habitat loss through land use changes. Scientists estimate that 5,000 iguanas currently inhabit Mona Island, which is low compared to other Cyclura species that can reach densities up to 60 per hectare. Their low population density could be partially explained by competition with introduced ungulates and predation by feral cats. However, Pérez’ studies have revealed that the males are very territorial. “Maybe territorialism can help to explain the low population density because if iguanas do not share space with individuals of the same sex, the number of individuals in a given area will be limited. If this is true, then the Mona Island iguana population can be considered a healthy population with a social system that is molding its demography. Other Cycluras can live for 50 years, and females lay eggs every year. If the Mona iguana also lays eggs yearly, and they can live more than 25 five years, the population would be able to overcome adverse effects of, for example, feral cats on population recruitment. At the end of my dissertation I won’t have all of the answers about the population, but I will have compiled a lot of data to generate a mathematical model to figure out what is going on with the species and identify what we can do to assure that the species will survive.”

The University of Puerto Rico, Río Piedras and DNER have committed to continue researching the Mona iguana, to try to understand, for example, poorly known aspects of their biology such as the causes of a blindness syndrome that was reported on 1995. Scientists are also investigating how important iguana seed ingestion is for seed germination and dispersal and how threats to the health of iguana populations affect plant community dynamics. Pérez’ research has been funded by CREST-Catec, the International Iguana Foundation, and the University of Puerto Rico, Río Piedras.

A male Mona Island iguana (Cyclura coronuta stejnegeri) weighs between 6.5 and 11 kg. and a female between 4.5 and 8.5 kg. (Photo by Waldemar Alcobas)

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