Initial Population Study of the Iguana iguana across San Juan National Historic Site (SJNHS)
Turner O, Naveira Guzman M, Gomez Ortiz M, Malave Hernandez S, Sepulveda Mangual A. 2026. Initial Population Study of the Iguana iguana across San Juan National Historic Site (SJNHS). National Park Service. San Juan, Old San Juan, Puerto Rico. https://doi.org/10.36967/2321083
The San Juan National Historic Site (SJNHS), the only National Park Service (NPS) unit in Puerto Rico, contains European fortifications dating back to the 16th century and a variety of coastal and urban microhabitats. The expansion of I. iguana within the park poses risks to cultural resources, public health, and the environment. This project establishes a quantitative baseline of abundance and density to guide the Green Iguana Management Plan at SJNHS and to evaluate responses to future control actions. Four study zones were designed based on the presence/expected distribution of I. iguana, park boundaries, and accessibility. In each zone, Visual Encounter Surveys (VES) were conducted along ~130 m transects, twice daily (AM/PM), eight occasions per week, over five weeks. Each iguana sighting recorded age (neonate/juvenile/adult), sex (male, female, undetermined), and status (alive, dead, dying/unhealthy). Each survey also collected anthropogenic disturbance (low, medium, high), and climate variables (temperature, relative humidity, dew point, wind speed). Data were captured using ArcGIS Survey123 and analyzed in RStudio (regression analysis, non-parametric tests, and N-mixture modeling). A total of 603 individuals (including possible repeats) were counted in the 32 surveys. Paseo del Morro exhibited the highest densities; significant differences were found between zones, with no AM/PM effect. Wind speed was negatively associated with observed density at the park scale; other climate variables showed no consistent effects. The ecological model with the lowest AIC estimated 491 iguanas (range: 352–688) across 30.351 ha, with an average detection probability of 16.4% and an estimated density of 16.18 iguanas/ha (estimated density range of 11.59, 22.67 individuals/hectare). The observed and estimated densities justify targeted control actions (priority in Paseo del Morro), continuous monitoring, and evaluation of trapping effort. It is recommended to avoid fixed density objectives and to focus management on reducing risks to historic infrastructure, visitors, and natural resources, complementing trapping with measures addressing habitat and fecundity to mitigate demographic compensation.
- Type
- Published Report
- Authors
- Turner, Olivia; Naveira Guzman, Miguel; Gomez Ortiz, Mariela; Malave Hernandez, Stephanie; Sepulveda Mangual, Adriana
- Date of Issue
- 2026-10-01
- Publisher
- National Park Service
- DOI
- 10.36967/2321083
- Units
- SAJU
- Keywords
- abundance estimation, climate variables, cultural resource protection, density estimation, detection probability, ecological modeling, habitat use, Iguana iguana, invasive species, microhabitats, natural resource management, N‑mixture modeling, NPS Wildlife Program, population monitoring, Puerto Rico, San Juan National Historic Site, SER Region, SJNHS, urban ecology, Visual Encounter Surveys, wildlife management, wind speed
- Subjects
- Ecological Framework: Biological Integrity | Invasive Species | Invasive/Exotic animals