Changing winter conditions in the boreal forest : the effects of fluctuating temperature and predation risk on activity and physiological stress level in bank voles

Abstract

Due to global climate change, the winter conditions in the North are predicted to change, as the time with an intact insulating snow cover gets shorter or disappears altogether. For small mammals, this could cause exposure to strong temperature fluctuations and increased predation risk, inducing severe stress and leading to alterations in the physical condition and behavior. To test this, we exposed bank voles (Myodes glareolus) to different temperature regimes and cues of predator threat under laboratory conditions. The test animals experienced either a stable but cool temperature regime resembling the stable conditions under snow cover, or an unstable temperature regime with cold nights and warmer days simulating the climate change scenario with unstable winter. After 3 weeks, the animals were additionally exposed to owl calls or sounds of non-predatory bird species. Stress levels, activity, food consumption, and body mass were monitored. We observed that the voles exposed to unstable temperatures adjusted their normal, mostly nocturnal, and circadian activity pattern towards a more diurnal rhythm without any significant responses in their stress level. Introducing the sound manipulation elevated the stress levels in females but not in males. The sound-induced stress levels did not differ between the temperature treatments. However, the temperature regime tended to affect anti-predator behavior as individuals experiencing unstable temperatures and a threatening sound decreased their overall activity, unlike individuals under stable temperature treatments. It seems that behavioral plasticity in bank voles may diminish the risk of accumulation of stress in cases of multiple simultaneous stressors.