2017 Fieldwork south of Lago Enriquillo
Interspecific interactions, ecology, and conservation of Cyclura cornuta and Cyclura ricordii south of Lago Enriquillo
Report submitted by Christopher M. Pellecchia, Stesha A. Pasashnik (Fort Worth Zoo), and Carl P. Qualls, University of Southern Mississippi
Photos by Christopher Pellecchia unless otherwise noted.
The Dominican Republic features a unique ecological phenomenon within the genus Cyclura: the sympatry of two species of rock iguanas: the Critically Endangered Ricord’s Rock Iguana (Cyclura ricordii) and the Vulnerable Rhinoceros Iguana, (Cyclura cornuta). Grupo Jaragua (GJ) and the International Iguana Foundation (IIF) have made immense conservation strides for both species in the Pedernales region of the Dominican Republic, as well as monitoring of iguanas south of Lago Enriquillo since the 2002 Ricord’s Species Recovery Plan. However, in the area south of Lago Enriquillo, both species face intense threats of habitat loss and degradation due to the illegal charcoal industry, agriculture, poaching, and invasive species.
For the 2017 field season, we investigated the distribution, population demographics, and burrow ecology of both species of Cyclura south of Lago Enriquillo. We also searched for critical nesting habitat locations and examined the roles in which geological features, such as canyons, may impact the ecology of both species. We used camera traps, a burrow camera system, and live-traps to survey across the region from 18 June to 14 August 2017. The field team consisted of Christopher Pellecchia from University of Southern Mississippi, Stesha A. Pasachnik, Ph.D. from Fort Worth Zoo, and M. Anibal Volquez, Jerbin Volquez, and Winston Volquez from Grupo Jaragua.
Population demographics and morphometrics. We deployed 24 live-traps across 17 locations during our field season. We captured a total of 104 Cyclura ricordii and 23 Cyclura cornuta. We implanted PIT tags in 101 Cyclura ricordii and all 23 Cyclura cornuta. We also recaptured a lone juvenile Cyclura ricordii which received a PIT tag during a 2016 trip to the region. With so many iguanas now PIT-tagged, the opportunity for detailed long-term population monitoring using mark-recapture methods is possible. Upon capture, iguanas were measured, weighed, marked, and PIT-tagged. We also took tissue samples from each individual, which will later be used for genetic analysis. Detailed photos were taken of each individual iguana, which we hope to integrate in a digital morphometric analysis at a later date.
Species distribution and habitat modeling. We used eight Bushnell Trophy camera traps in 18 locations during our field season, to determine iguana presence or absence across a variety of habitats. These camera traps also recorded daily activity patterns of both species of iguana, as well as invasive species such as feral cats, and the Endangered endemic Hispaniolan Solenodon, Solenodon paradoxus. We also collected data on dominant plant species, substrate type, canopy cover, ground cover, anthropogenic impacts, signs of invasive species at burrow locations, iguana sightings, and where iguanas were captured. These data will be used as parameters in a resource selection model to determine habitat and resource availability and preference for both species.
Burrow ecology. The team examined 92 iguana burrows at 13 sites with a custom burrow scoping system. We found iguanas in 27 of those burrows, confirming Cyclura ricordii presence in 24 burrows and Cyclura cornuta presence in three burrows. We also found one invasive amphibian species and a minimum of seven commensal species including various insects, arachnids, and small reptiles using the Cyclura burrows. We believe this minimally-invasive survey method could be helpful in other studies of Cyclura. We observed individual iguanas using multiple burrows and multiple iguanas using a single burrow. Surprisingly, we also observed Cyclura cornuta and Cyclura ricordii using the same retreat burrow. Our camera traps monitored iguana activity around a single burrow, and we observed long periods of daily iguana presence followed by daily periods of absence. This may suggest that iguanas are regularly using more than one burrow within their territory, which may alter previously used population estimation methods where a single burrow is counted as one iguana.
Nesting habitat and nesting ecology. The team found five Cyclura nests at four sites. We suspect three of these were Cyclura ricordii nests and two were Cyclura cornuta based on stage of development, nest location, and timing within the breeding seasons of each species.
Charcoal industry and poaching. The illegal charcoal production industry south of Lago Enriquillo created an immense obstacle for the field team this season, and is considered one of the greatest threats to Cyclura in the Dominican Republic. The epicenter of this industry occurs in our focal region. We discovered actively burning charcoal kilns, ‘carboneros’ (illegal charcoal workers), and illegal mines within 100 meters of our study sites. The carboneros not only pose a threat to iguana’s habitat, but often these individuals are also ‘iguaneros’ (illegal iguana poachers) who harvest iguanas as they clear-cut the land. Iguanas are sold for consumption or less frequently for the illegal pet trade. We identified five major active charcoal operations near our study sites. We also discovered and removed many illegal snare traps placed at Cyclura burrow entrances within our study sites. At one charcoal camp, we discovered the remains of at least nine iguanas (both Cyclura cornuta and Cyclura ricordii), presumably eaten by the carboneros. We reported all active charcoal operations to the Ministry of Environment and Natural Resources (Medio Ambiente RD) through Grupo Jaragua.
Future. We will continue with our 2017 field season methods during the summer of 2018. We will expand our surveys, trapping, camera trapping, and burrow scoping to cover the western portion of the area south of the lake. We also aim to expand our knowledge of Cyclura burrow use, densities, and abundance. Any information regarding Cyclura burrow use in the Dominican Republic could be applicable to other Cyclura species. We hope to begin an iguana mark-recapture program which will require revisiting our 2017 sites annually. This could yield valuable data on population dynamics, community ecology, and the impacts of poaching for each species. We plan to continue our habitat data collection and use fresh aerial imagery (satellite, aircraft, and/or drone) to refine our resource selection model, burrow ecology study, and charcoal monitoring effort. Lastly, we hope to conduct fine scale genetic analyses of both species within the region. We will request funding from the International Iguana Foundation in 2018 to continue these efforts.