Red-tailed boa (Boa constrictor) surveys at Salt River Bay National Park, St. Croix U.S. Virgin Islands: 2023 report of activities

Abstract

St. Croix is home to a variety of threatened and endangered (T&E) species that are at risk for predation by the invasive red-tailed boa (Boa constrictor), such as the St. Croix ground lizard (Amevia polyps), the ground-nesting least tern (Sterna antillarum), and the hawksbill sea turtle (Eretmochelys imbricata). Genetic analysis determined the original red-tailed boa population on St. Croix sourced from a single female released by a pet owner and its range expands every year. Presently, the main population of red-tailed boa is established on the west end of St. Croix and extends as far east as Salt River. One individual was found in Salt River Marina and additional sightings have occurred in Salt River Bay National Historical Park and Ecological Preserve (SARI) more recently. This inventory aims to search for red-tailed boas in two focal areas that park staff are actively restoring. The park will use information from this inventory to develop a boa removal program and protect sensitive native species like the ground-nesting least tern, the St. Croix ground lizard and the hawksbill sea turtle nests and increase the success of restoration. Snakes are cryptic species, often occurring in low density, and utilize complex habitat patterns. To increase the likelihood of detecting red-tailed boa, the Maryland/Delaware/D.C. Wildlife Services detector dog handling team partnered with the USDA-APHIS National Detector Dog Training Center to train and develop detector dogs to assist in determining the presence/absence of red-tailed boa for this project. Canines were trained to locate red-tailed boa and indicate its presence to the handler via barking three times near the identified target. Two dog detector teams traveled to Salt River Bay National Park (SARI) in St. Croix to conduct surveys for red-tailed boa in habitats likely to contain red-tailed boa in June 2023. Habitat varied throughout the surveys. Close to the bay, mangrove forests dominated and, as elevation increased, transects took place in almost exclusively dry tropical shrub forest. Each transect was surveyed by one dog team. The canine teams had no red-tailed boa detections within SARI. Canines showed proficiency at surveying for red-tailed boa populations in SARI. Given the proximity of confirmed detections to SARI, it is likely red-tailed boa will be in the park in the future, if they are not already. Additional surveys, whether by humans, canines, or both, are recommended in areas of the park that have not been previously surveyed.