AZA Species Survival Plan Profile

Mona/Virgin Islands Boa

A U.S./Puerto Rico Partnership Seeks to Recover Endangered Boa

By: Peter J. Tolson and Miguel A. Garcia

The Mona boa (Epicrates monensis monensis) and the Virgin Islands boa (Epicrates m. granti) are endemic to Isla Mona and the Puerto Rico Bank, respectively. While the Mona boa is confined to Isla Mona, the Virgin Islands boa inhabits a constellation of islands from Puerto Rico eastward into the British Virgin Islands. Both boas are small, attractively mottled brown snakes that live in coastal forest. Their nocturnal habits and retiring nature make them largely inconspicuous and difficult to locate. As a result, the boas have rarely been the victims of direct human persecution. In fact, when conditions are favorable, this species can exist in high densities on small islands. However, large-scale habitat destruction and the introduction of exotic mammalian predators (e.g., rats, cats) have put these taxa in extreme peril over most of their range. The Virgin Islands boa is listed as endangered and the Mona boa as threatened under the Endangered Species Act.

The Mona/Virgin Islands boa Species Survival Plan (SSP), set up in 1990, initially emphasized management in captivity. The focus has recently shifted to management of wild populations. Findings from a comprehensive research program indicated that active management of extant populations in the field was more likely to lead to the recovery of the species than a captive propagation program. The U.S. Fish and Wildlife Service (FWS) Caribbean Field Office, the Departamento de Recursos Naturales y Ambientales de Puerto Rico (DRNA), and the Division of Fish and Wildlife, U.S. Virgin Islands (USVI) cooperated in the development and publication of the FWS Recovery Plan for each subspecies (FWS 1984, 1986). The Recovery Plan resulted in the first reintroduction of American Zoo and Aquarium Association (AZA) SSP reptiles into the wild.

Field studies

One of the first steps in implementing recovery activities was intensive survey work at localities likely to harbor previously unknown populations (FWS 1984, 1986). The offshore cays of Puerto Rico and the USVI, the majority of which are free of cats and mongooses and have large tracts of littoral forest, were surveyed by staff of the Toledo Zoological Gardens (TZG). A previously undescribed population of the Virgin Islands boa was discovered on Isla Culebra, Puerto Rico. However, no additional populations have been discovered on other Puerto Rican or USVI cays.

A longitudinal study of an isolated population of the Virgin Islands boa was initiated in 1984. Lasting nine years, the effort yielded demographic and ecological information from more than 650 captures of over 300 marked individuals. Analysis of the ecological information indicated that boas were most successful in habitat that had few or no exotic predators and was primarily composed of relatively dense vegetation with an interlocking canopy (Tolson 1988). Further studies (Chandler and Tolson 1990) elucidated the foraging strategies of these snakes. Ecological work was later expanded to include field research in 1991-92 on the ecology and demography of the Virgin Islands boa on Isla Culebra, Puerto Rico and the USVI. Current SSP research is concerned with analysis of survivorship of different age classes of the reintroduced population of the Virgin Islands boa and ecological studies of the Mona boa. Data gathered from the latter will be used to revise the FWS Mona Boa Recovery Plan (FWS 1984).

Captive management and reintroduction

A captive breeding program using the Virgin Islands sub-species was initiated by TZG in 1985. The first successful captive breeding occurred in 1986 (Tolson 1989) with subsequent publication of the AZA-sanctioned Regional Studbook in 1987, and development of the SSP. The SSP program emphasizes short-term maintenance in captivity for the production of snakes for reintroduction programs. The basis for this management strategy was developed under the FWS Recovery Plan for the Virgin Islands boa (FWS 1986). These efforts were coupled with a comprehensive reproductive research program using the Cuban boa (E. angulifer) and the Haitian boa (E. striatus) as models, which established the proximate environmental and social factors critical for reproduction in this species (Tolson and Teubner 1987; Tolson 1994). The reproductive program has been very successful, producing more than 100 offspring from ten founders. Representatives of two populations of the Virgin Islands boa, one from Puerto Rico and one from St. Thomas, USVI, are being managed in captivity as two separate genetic units (i.e., individuals from the two populations are not cross bred) as each population exhibits a distinct coloration. These two populations have lately been shown to exhibit differences in mtDNA restriction enzyme cleavage sites (Gach, Tolson and García, unpublished data). A breeding program for the Mona boa, used primarily for reproductive research on this taxon, was initiated in 1995.

Exotic predators pose the greatest danger to successful reintroduction efforts. Cats, which prey on adult boas, are already ubiquitous on St. Thomas, USVI. A study to assess the status of the Isla Mona feral cat population and the magnitude of the impact of cat predation on Isla Mona wildlife has been initiated by the DRNA with assistance from the SSP. A rodent poisoning program was initiated on three islands identified as potentially suitable for reintroduction (i.e., Congo Cay, USVI; Cayo Ratones and Isla Monito, Puerto Rico). Elimination was attempted through three rounds of anti-coagulant poisoning spaced six months apart. Rats have been eliminated on Cayo Ratones, while on Congo Cay rats were undetected for two years after poisoning but have since returned. The poisoning of Isla Monito's rats is still in progress.

The careful background work and planning described above resulted in reintroduction of 28 zoo-born snakes on Cayo Ratones, Puerto Rico, in August 1993; an additional seven were released in November 1994. Six of the released snakes were implanted with radiotransmitters to monitor their activities. The reintroduction effort, funded by the AZA Conservation Endowment Fund, has been an outstanding success. Quarterly monitoring during the first year, funded by the FWS, established minimum survival estimates of 82.6% through August 1994. Reproduction occurred at least twice in the reintroduced population during the first breeding season, and all of the seven offspring known to have been born on the cay were recaptured at least one year after their birth.

Conservation outreach programs

To ensure expertise is transferred to local conservation authorities and students, the TZG has worked closely with the DRNA in all phases of the recovery process. DRNA biologists have accompanied field research parties on most research and management activities, and Puerto Rican students are given first priority for employment as field assistants. Three DRNA biologists visited the TZG in 1992 to gain skills in basic boa husbandry and techniques for reproduction. A mentoring program was implemented in 1995 with the Center for Reproduction of Endangered Species at the University of Puerto Rico at Humacao and has resulted in exchange visits of the TZG conservation, curatorial, and veterinary staff to Humacao, and visits of two professors and a technician from the University of Puerto Rico to TZG.


The conservation program for these two boas has collected critical demographic, ecological, and reproductive information and has documented the status of several key populations of the boa. Expertise has been shared with local university and management staff as well as with the wider conservation community through papers and presentations. Perhaps most significantly, a successful short-term reintroduction of the species to a locality within their historical range has provided valuable insights into strategies useful in snake reintroductions. Future activities include: (1) monitoring the reintroduced population of the Virgin Islands boa for a full 10 years; (2) collecting additional data on the Mona boa; and (3) increasing management efforts on Isla Mona (e.g., restoring degraded forest habitat and controlling exotics).


Support for the conservation of the Mona/Virgin Islands boa has been provided by the U.S. Fish and Wildlife Service; the Institute of Museum Services-Conservation Project Support; the AZA Conservation Endowment Fund; the Departamento de Recursos Naturales y Ambientales, Puerto Rico; the Walt Disney Company through the AZA Conservation Excellence Campaign; the Division of Fish and Wildlife, U.S. Virgin Islands; and the Toledo Zoological Society. The authors are grateful to Carlos E. Díez, Valerie Hornyak, Luis O. Nieves, James P. Oland, Pablo M. Reyes, Jorge Saliva, and our many colleagues from the Departamento de Recursos Naturales y Ambientales, Puerto Rico and the Toledo Zoological Gardens who have given so selflessly to this project.

Literature Cited

Chandler C.R. and P.J. Tolson. 1990. Habitat use by a boid snake (Epicrates monensis) and its anoline prey, Anolis cristatellus. Journal of Herpetology 24(2):151-157.

Tolson, P.J. 1988. Critical habitat, predator pressures, and management of Epicrates monensis on the Puerto Rico Bank: a multivariate analysis. Pages 228-238 in R.C. Szaro, K.E. Severson, and D.R. Patton, editors. Management of amphibians, reptiles, and small mammals in North America. USDA Forest Service General Technical Report RM-166.

Tolson, P.J. 1989. Breeding the Virgin Islands boa, Epicrates monensis granti, at the Toledo Zoological Gardens. International Zoo Yearbook 28:163-167.

Tolson, P.J. 1994. The reproductive management of insular species of Epicrates (Serpentes:Boidae) in captivity. Pages 353-359 in J.B. Murphy, J.T. Collins and K. Adler, editors. Captive management and conservation of amphibians and reptiles. A Volume Honoring Roger Conant. SSAR Contrib. Herpetology Volume 11.

Tolson, P.J. and V.A. Teubner. 1987. The role of social manipulation and environmental cycling in propagation of the boid genus Epicrates: lessons from the field and laboratory. Pages 606-613 in American Association of Zoological Parks and Aquariums Regional Conference Proceedings. American Zoo and Aquarium Association, Wheeling, West Virginia.

U.S. Fish and Wildlife Service. 1984. Mona Boa Recovery Plan, U.S. Department of the Interior Fish and Wildlife Service, Atlanta, Georgia. 16 pp.

U.S. Fish and Wildlife Service. 1986. Virgin Islands Tree Boa Recovery Plan, U.S. Fish and Wildlife Service, Atlanta, Georgia. 23 pp.

Peter J. Tolson is the Mona/Virgin Islands boa SSP Coordinator. He is based at the Toledo Zoological Gardens, P.O. Box 4010, Toledo, OH 43609. Miguel A. Garcia is the Endangered Species Coordinator at the Deparamento de Recursos Naturales y Ambientales de Puerto Rico, Apartado 5887, Puerta de Tierra, PR 00906.

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