Sub-zero body temperatures during early spring migration in blue-spotted salamanders (<i>Ambystoma laterale</i>)

Amphibians that reproduce in early spring at northern latitudes may encounter environmental ice while migrating to their breeding sites. Due to the nucleation properties of ice, contact with environmental ice may induce rapid freezing of body tissues, which can cause irreversible damage to cells and lead to death. Although some species of salamanders are known to move over ice during early spring migration, freeze-intolerant species are expected to avoid physical contact with ice crystals to minimise the risk of freezing. Here, we documented the thermal biology of the freeze-intolerant blue-spotted salamander ( Ambystoma laterale Hallowell, 1856) migrating at sub-zero temperatures in Algonquin Provincial Park, Ontario, Canada. During our surveys, we found sheltered, inactive, and migrating individuals; some in direct contact with ice. Our field measurements of skin temperature using high-resolution thermal imaging suggest that A. laterale can sustain activity in sub-zero temperatures, possibly in a supercooled state (i.e., chilled below the freezing point of body fluids but not frozen). By migrating in such conditions, these salamanders may overcome the risk of freezing while simultaneously prolonging their breeding season and potentially avoiding predators.