Overwinter behavior, movement, and survival in a recently reintroduced, endangered amphibian, Rana muscosa

Basic natural history information is critical for species conservation but is often deficient for endangered species, which can be rare and difficult to study. This is particularly true for behavior and natural history during the winter in temperate regions, when site access can be challenging. For translocation programs in temperate regions, however, winter may be a critical time to assess movement, survival, and threats to persistence in order to understand the causes of translocation failures. Using radiotelemetry, we monitored movement from fall through spring in reintroduced, ex situ bred individuals (N = 21) of the endangered mountain yellow-legged frog (Rana muscosa) to characterize behavior during brumation (overwinter dormancy), overwinter infection prevalence of the fungal pathogen Batrachochytrium dendrobatidis (Bd), and survival. We found that movement rates were variable but low in comparison to other sites. Frogs moved more in the fall when temperatures were warmer in comparison to the winter and spring. However, some frogs still moved (very small distances) even when water temperatures were below 2 °C and snow covered the ground. Frogs were difficult to detect visually, but were almost always in water, including during brumation, when they usually appeared to be in underwater rock caves and crevices in pool habitat. Frogs appeared to be spatially clustered in 3–5 groups throughout the study period and those within a group were often located <1 m from one another. Overwinter survival rates were low: over 70% of animals were confirmed dead, and all were suspected dead by mid-May. While sample size was limited, Bd prevalence and infection intensity increased during the winter and spring, which may have contributed to mortality rates. This study sheds light on a poorly understood life history phase for an endangered amphibian and will inform future management activities to protect this species.