Snake fungal disease affects behavior of free-ranging massasauga rattlesnakes (Sistrurus catenatus)

Snake fungal disease (SFD) caused by Ophidiomyces ophiodiicola can lead to morbidity and mortality in snakes. However, we know little about the behavior of free-ranging individuals with the disease and the implications this may have for threatened taxa. We discovered Massasaugas (Sistrurus catenatus), a federally protected rattlesnake in eastern USA, with SFD in northern Michigan during a radio-telemetry study we conducted from 2013–2017. We were consequently provided with an opportunity to investigate differences in movement, visibility, thermoregulation, and overwintering site selection between eight infected and 17 uninfected snakes. Across the active season, infected snakes moved distances ≥ 10 m less frequently and were less visible than uninfected snakes. This suggests disease imposed an energetic cost of movement too great for debilitated snakes that was possibly outweighed by other behaviors, such as avoiding predators. Monthly body temperatures of infected snakes differed from uninfected snakes only near the end of the active season, supporting observations of infected snakes surface basking when uninfected snakes had retreated to overwintering refugia. Most infected individuals overwintered in a concentrated area, suggesting environmentally driven hotspots for the fungus could exist within the landscape. Our findings provide a baseline for future studies investigating more consequential behavior for infected snakes. Linking snake behavior with the distribution of the fungus and habitat features at localized scales will ultimately lead to increased epidemiological knowledge of SFD, which could aid management and conservation efforts for imperiled species such as Massasaugas.