Hibernation behavior of a federally threatened ground squirrel: climate change and habitat selection implications

Hibernation is an adaptation to survive periods of stress, from food limitation or harsh thermal conditions. A key question in contemporary ecology is whether rare, range-restricted species can change their behavior in response to climate change (i.e., through behavioral plasticity). The northern Idaho ground squirrel, Urocitellus brunneus (A. H. Howell, 1928), is a federally threatened species that hibernates for approximately 8 months per year within the bounds of its small range in central Idaho, USA. Changes in temperature, snow accumulation, and summer precipitation, all brought about as a result of climate change, may reduce survival or fecundity of northern Idaho ground squirrels if they cannot adapt to these climate changes. Hibernating species can respond to climate-change-induced thermal challenges in two ways: change their hibernation physiology and behavior (i.e., emergence date or number of torpor bouts) or alter their environment (i.e., change hibernacula depth or location). We explored a suite of intrinsic and extrinsic factors to document the extent to which they influenced hibernation behavior of northern Idaho ground squirrels. Emergence date was positively associated with snowpack and negatively associated with mean winter temperature. Mean minimum skin temperature was negatively associated with canopy closure and slope of a squirrel's hibernaculum. Duration of the heterothermal period, number of euthermic bouts, and total time spent euthermic were positively associated with body mass. Immergence date and duration of the longest torpor bout were negatively associated with body mass. Warmer temperatures and less snow accumulation in the winter—caused by climate change—likely will cause altered emergence dates. Our results suggest that any future climate-induced changes in snowfall, ambient temperature, food availability, or habitat likely will impact survival of this rare ground squirrel, because such changes will cause changes in hibernation behavior, percent mass loss during hibernation, and duration of the active season when small mammals are more susceptible to predation.