Individual Identity and Environmental Conditions Explain Different Aspects of Sleep Behaviour in Wild Boar

Sleep is a fundamental behaviour as it serves vital physiological functions, yet how the sleep of wild animals is constrained by environmental conditions is poorly understood. Using non-invasive multi-sensor high-resolution biologgers and a robust classification approach, we quantified multiple dimensions of sleep in wild boar (Sus scrofa), a nocturnally active mammal, monitored for up to a full annual cycle. In support of the hypothesis that environmental conditions determining thermoregulatory challenges regulate sleep, we show that on warmer, longer, and more humid days sleep quality and quantity are reduced, whilst greater snow cover and rainfall promote sleep quality. Importantly, our study reveals large inter-and intra-individual variation in sleep durations, suggestive of pace-of-life syndromes. Given the major role that sleep plays in health, our results suggest that global warming and the associated increase in extreme climatic events are likely to negatively impact sleep, and consequently health in wildlife, particularly in nocturnal animals.