Hibernation of the Eastern Massasauga rattlesnake ( Sistrurus catenatus catenatus) in northern Michigan

Hibernation sites at high latitudes must protect snakes from subfreezing conditions for long periods of time. Thus hibernation is an important part of snake life histories in these regions. Despite this fact little is known about the hibernation ecology of north temperate snakes, and this lack of understanding regarding the factors that influence overwintering success may hinder management efforts for declining species. The Eastern Massasauga Rattlesnake (Sistrurus catenatus catenatus) is a declining species which appears to have highly specific but poorly understood hibernation requirements. To address this gap in our knowledge, I conducted a study to assess hibernation site selection and overwintering ecology of the Eastern Massasauga in northern Michigan. This population studied is of particular interest because it is near the northern range limit of the species, occurs in a large relatively undisturbed area, and burrowing crayfish are absent. Hibernation sites were located using radiotelemetry. Visual inspections with a fiber-optic borescope were made to examine the activity of snakes during winter months, and their relationship to groundwater. Groundwater and soil sampling was conducted to determine if physical and chemical parameters of groundwater and soil could be used to discriminate between hibernation and control sites. Using binary logistic regression, I identified water table depth, water and soil pH, soil organic matter, and soil texture as predictor variables for the locations of hibernation sites. Massasaugas hibernated in root systems and mammal burrows in mostly forested habitats, and spent most of the winter submerged. They selected sites where the water table was close to the surface, but safe from flooding, and not necessarily adjacent to wetlands. Massasaugas in this population typically traveled several hundred meters between hibernation sites and activity centers, and demonstrated high rates of site fidelity. Communal hibernation was observed for the first time in this species. Observations of massasaugas sharing hibernacula with conspecifics, coupled with their strong site fidelity and long seasonal migrations indicate that suitable hibernation sites may be limited in this landscape. Additionally, the distribution of hibernation sites in habitats with intermediate water table depths indicates that these snakes may be sensitive to changes in groundwater levels. The identification and protection of hibernation sites is an important part of the management and recovery of this declining species. My observations of this population indicate that massasaugas may be unable to respond to land management activities that impact hibernacula. Known hibernation sites should be treated with extreme care. Water table manipulations that may drop or raise groundwater levels during winter should be avoided in landscapes that contain massasauga populations to improve their chances of surviving hibernation