Overwintering under ice: A novel observation for an Australian freshwater turtle.

Frozen water bodies provide a physiological challenge to fauna by physically limiting access to atmospheric oxygen. To tolerate low temperatures, reptiles use brumation as a physiological strategy in winter. Cryptodira vary in their tolerance to freezing conditions but the extent of tolerance in pleurodirans is largely unknown. Australia's freshwater turtles inhabit warmer regions with less severe winters and have well-developed mechanisms to cope with high temperatures and drying waterbodies, rather than extreme cold tolerance. Chelodina longicollis is a widespread Australian freshwater turtle species that tolerates high temperatures and desiccation during hot, dry periods while also undergoing brumation during winter months. Despite extensive research, limited observations exist on their behaviour during severe winter periods at the extremes of their range. In an 11-month tracking study, we monitored adult C. longicollis , noting their movements, locations, and temperature weekly. We observed an adult female C. longicollis which, during a seven-month period within a single creek pool, survived brumation in extreme cold water including a 15-day period of total freezing of the surface water. After the ice melted following a rain event, the turtle was recaptured alive. This marks the first observation of brumation for an Australian chelid species under ice.