Beavers on Ice: Factors Influencing Emergence Phenology in Boreal Canada

The influence of climate change on emergence phenology of hibernating mammals in northern latitudes is receiving increased attention, yet for freshwater semi-aquatic mammals such as beavers, which do not hibernate and therefore maintain an obligatory dependence on freshwater habitats throughout the year, little is known about factors influencing their spring emergence above the ice. Given documented effects of increased warming on patterns of ice formation and ice duration on boreal lakes and ponds, we recorded the date of beaver emergence from their winter lodge onto the ice from 2008 to 2025 (18 years) to examine the possible role of temperature, precipitation, and ice phenology on timing of beaver emergence in the spring. On average, ice-on to emergence lasted 144 days (min 124.0, max 173.0) with a mean emergence date of April 1st. Increased length of the ice-free period prior to winter, total precipitation and average temperature from spring ice-off to the next year's emergence were the best predictors of beaver emergence in spring. Temperature was the best predictor of variation in ice duration, while total precipitation from spring ice-off to ice-on and average maximum summer temperature appeared to influence the ice-on date. Trend analyses revealed increasing annual maximum mean temperatures, with increasing summer temperatures being most apparent. With longer ice-free periods, beavers can forage longer and store more food for winter access; however, longer periods of open water also increase the period that their activities expose them to increased conflict with humans. Understanding the influence of climate change on the ecology of non-hibernating, yet ice-bound mammals provides greater insights into future management of these species.