Thermal characteristics of overwintering habitats for the Blanding’s Turtle (Emydoidea blandingii) across three study areas in Ontario, Canada

Habitat restoration is a necessary strategy to protect populations of Blanding’s Turtles (Emydoidea blandingii) living in settled areas. Relatively little is known about thermal tolerances and requirements of this species in situ during the overwintering period, except that these turtles must find water bodies that do not freeze completely and that are sufficiently cool to allow them to stay dormant throughout the winter. We used water temperature data associated with Blanding’s Turtle populations in a northern, central, and southern study area within Ontario, Canada to determine thermal characteristics of occupied overwintering habitats. From fall through spring from 2012 to 2014, we measured water temperature of 20 potential overwintering habitats within the three study areas. We also radio tracked 48 adult turtles to determine which habitats they occupied during winter. Water temperatures of all occupied habitats ranged from 0.44° C to 3.68° C, with a mean of 1.77° C (± 0.03° C), and showed slow steady declines throughout the overwintering period. Regardless of location, average water temperatures at all confirmed overwintering habitats remained above the freezing point of turtle body fluids (-0.6° C). Average water temperature at five of the six confirmed overwintering habitats never dropped below 0° C, but dropped to -0.33° C for eight days at the sixth overwintering habitat. Determining thermal parameters of overwintering sites can provide knowledge useful for habitat restoration and creation to ensure habitats provide suitable overwintering conditions in the face of global climate change.