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 the global climate change the winter conditions in the North are predicted to change, as the time with an intact snow cover gets shorter or disappears altogether. Many small ground dwelling animals, like rodents, are strongly dependent on protection provided by snow cover against cold and predators. Thus, lack of proper snow cover causing exposure to strong temperature fluctuations and increased predation risk could induce severe stress, causing alterations in the physical condition and behavior, and eventually lead to lower winter survival. 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 diel temperature regime with cold nights and warmer days simulating the climate change scenario with unstable winter. After three 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 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. However, the laboratory born voles were not able to distinguish between the sound of the non-predatory control bird and predatory bird and seemingly considered both as a threat. 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 temperature and a threatening sound decreased their overall activity, unlike individuals under stable temperature treatments. Our results suggest that the ability of bank voles to plastically adjust their behavior may diminish the accumulation of stress when exposed to multiple stressors simultaneously.

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“…We used blinded methods for data collection, recording and analyses to minimize potential observer bias as described by Sipari et al . (2016).…”

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“…Similarly, it was discovered that the dramatic decline in bee populations as a reaction to pesticides and land use changes has led to a loss of pollination, one of the most important ecosystem functions. There exist many studies examining the effect of forest fragmentation and forest patch size on the physiological stress response in forest animals and animal communities [439][440][441]. Therefore, animals are crucial bio-indicators of disturbances, stress and environmental changes.…”