Most wildlife goes into hibernation in autumn. It’s the most efficient way of surviving winter. Rather than searching for food (of which there’s very little), they shut down and sit it out.
True hibernation involves slowing of the heart rate and breathing, and dropping body temperature, but most enter a state of ‘torpor’, where body temperature falls only slightly. They wake periodically and bring their body temperature back to normal, before returning to sleep. It’s not fully understood why they do this, but it may explain occasional hedgehog or bat sightings in winter.