Field ecology of freezing: Linking microhabitat use with freezing tolerance in Litoria ewingii

A small number of vertebrate species, including some frogs, are freezing tolerant and survive ice forming in their bodies under ecologically relevant conditions. Habitat use information is critical for interpreting laboratory studies of freezing tolerance, but there is often little known about the winter habitat and behaviours of the species under study. This work describes microhabitats used by the freezing-tolerant frog Litoria ewingii Dumeril and Bibron 1841 and their temperature characteristics. In winter, L. ewingii used microhabitats with wood, located further away from water than in summer. Microhabitat temperature records showed that frog microhabitats regularly fell below the temperature at which frog body fluids freeze (−1°C), and cooled substantially more slowly than did the air temperature. Temperatures were highly variable between microhabitats, seasons and years, with a minimum of −2.4°C and a maximum cooling rate of 0.77°C h−1. Frozen frogs were observed to recover in the field, demonstrating freezing tolerance. Both the characteristics of microhabitats and their selection are important in ensuring freezing survival.