Micrometeorological variability and climate change affect snake overwintering habitat resilience

• Changing winter climates will alter peatland overwintering habitat conditions. • Temperature, precipitation, and snow accumulation affect overwintering conditions. • Under climate change, we expect most peatlands to grow warmer and wetter. • Massasaugas may face increased future risk of flooding in overwintering habitats. • Resilient peatland overwintering habitat must be resistant to rising water tables. Snakes at northern latitudes can spend over half the year in their overwintering sites to avoid exposure to unsuitable weather conditions. However, with changing weather patterns driven by climate change, we hypothesized that warming winters could reduce the snowpack, thereby diminishing its insulating ability and compromising the stability of overwintering habitat conditions. We collected micrometeorological data from 2018–2024 in 10 peatlands near the northern range limit of the at-risk Eastern Massasauga rattlesnake ( Sistrurus catenatus ). We quantified suitable overwintering conditions for these peatlands by monitoring the life or resilience zone - the subterranean space above the water table and below the 0°C isotherm that could function as suitable overwintering habitat. We found that winters with warmer temperatures were associated with more favourable resilience zone conditions, while greater snow accumulation was linked to poorer overwintering conditions. However, towards the end of winter in February and March, warmer temperatures were linked to snowmelt, rising water tables, and subsequent resilience zone loss. We also used climate projections under shared socio-economic pathways to model future resilience zone conditions that predicted shallower freezing depths and rising water tables in most peatlands. As a result, some peatlands are expected to support a larger resilience zone while others may face prolonged flooding and loss of suitable overwintering habitat through compression or loss of the resilience zone. Though these variable outcomes suggest that suitable overwintering habitat will remain on the landscape, the implications for habitat currently used by snakes will depend on massasaugas’ tolerance to flooding versus freezing.