Beaver Spring Emergence and Ice Phenology

The response of hibernating mammals in northern latitudes to increased global temperatures influences population persistence over time. Their emergence phenology, the timing in the spring of when these mammals leave their overwintering dens or terminate hibernation, is often a key variable in assessing their reproductive and long-term ecological success. Although seasonally confined under the ice in northern climates, freshwater semi-aquatic mammals such as beavers (North American beaver, Castor canadensis; Eurasian beaver, C. fiber) do not hibernate and therefore maintain an obligatory dependence on freshwater habitats throughout the year as they move in and out of their winter lodges to access food. As with hibernating mammals, beavers emerge from their ice-bound lodges in early spring. These datasets document spring emergence phenology of North American beavers and allow for the assessment of climatic factors influencing their spring emergence above the ice. 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. Along with long-term climate trends (i.e., 30 years), we also recorded key aspects of ice phenology: 1) ice-on date – the day that the pond was completely covered in ice, and 2) ice-off date – the day that the pond was completely free of ice. 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. The four datasets represent 1) beaver emergence dates and associated climate and ice phenology variables, 2) ice duration data that documents the length of time the pond is covered in ice, 3) ice-free period for the year prior to beaver emergence to document the length of time that beavers are free to forage and move around the pond, and 4) long-term weather data that were used to use ARIMA models to assess weather trends over a 30-year period.