Assessment of a Locally Imperiled Snake (Sistrurus miliarius) and Estimation of Site Occupancy and Detection Probabilities of Sympatric Snake Species

Biodiversity declines have been occurring at alarming rates across the globe for the past two decades. Reptiles are currently experiencing rapid species declines due to a variety of stressors including habitat destruction, habitat alteration, and emerging pathogens. Snakes represent a taxon in widespread decline and can be difficult to study due to their cryptic morphology, minimal or sporadic movements, and use of inaccessible habitat. Due to these difficulties, there is a lack of data to evaluate conservation status or geographic distributions for many snake species. The pygmy rattlesnake (Sistrurus miliarius) is a common snake across the southeastern United States, but in Tennessee where this species is listed as State Threatened, is considered rare and imperiled. Further, geographic distribution data for this species is lacking in Tennessee. Therefore, we used species distribution modeling (Maximum Entropy Algorithm) to create a habitat suitability model to estimate the geographic distribution of S. miliarius and aide in prioritization of sampling efforts to ground-truth model results. We used standardized road cruising surveys to sample for S. miliarius and model occupancy and detection probabilities for detected snake species. Snakes encountered during surveys were further swabbed and then tested for the presence of Ophidiomyces ophiodiicola, the causative agent of snake fungal disease. Overall, our data suggests that the suitable habitat for S. miliarius is disjunct and minimal in Tennessee and predominantly occurs along riverine systems associated with the Tennessee River in the Interior Plateau and Southeastern Plains ecoregions. Detection probabilities were greatest in the late hours of the night and in the late Summer and early Fall months. We found that eleven out of 120 snakes tested positive for the presence of O. ophiodiicola. Positive cases occurred across four species and in four counties that further extended the known distribution of this pathogen in Tennessee. Our analysis highlights the potentially limited and sporadic suitable habitat for the rare and imperiled S.miliarius in Tennessee and provides researchers with a model of the estimated geographic range for the species that then can be used in future conservation efforts. Lastly, our research furthered our understanding of the distribution of the pathogen O. ophiodiicola in Tennessee that will better inform state agencies about the effect this pathogen is having on snake communities across the state