Date of Award
Detailed knowledge of a species’ range and distribution is important for understanding species persistence and developing species management plans. This issue is particularly pronounced in threatened species with wide-spread range and a low detectability in their natural environment, as surveying and successfully encountering this type of species is oftentimes difficult. One such species is the eastern massasauga rattlesnake (Sistrurus catenatus), a smallbodied pit viper with a distribution centered around the Great Lakes region. We used singleseason occupancy modeling in order to reassess the status of historic massasauga occurrences. We evaluated factors affecting eastern massasauga detection probability from a long-term dataset to inform a standardized survey protocol. We surveyed 34 sites throughout Michigan’s lower peninsula from May through September of 2018 and 2019. We measured site- and surveyspecific covariates at each site to inform occupancy and detection probabilities, respectively. Additionally, we used data from 2013-2019 collected from a population of massasaugas located in Southwest Michigan to inform detection-specific models. We found that average canopy cover best predicted occupancy probabilities, while total search effort best explained detection probabilities. From the long-term data, additive effects of total search effort, substrate temperature, the Julian day of year, and total site area best explained differences in eastern massasauga detection probabilities in Southwest Michigan. Our results may be used to guide future surveys efforts for the eastern massasauga at sites with unknown population status. Additionally, our findings suggest that eastern massasaugas may benefit from management plans that encourage reductions in average canopy cover while maintaining adequate refugia from predators and harsh conditions.
Thacker, Arin June, "Great Lakes Snake: Estimating the Occupancy and Detection Probabilities of the Eastern Massasauga Rattlesnake (Sistrurus catenatus)" (2020). Masters Theses. 984.