Hibernation the summer months is aestivation. Often associated with low temperatures, the function of hibernation is to conserve energy when sufficient food is unavailable. To achieve this energy saving, an endothermic animal decreases its metabolic rate and thereby its body temperature. Hibernation may last days, weeks, or months depending on the species, ambient temperature, time of year, and the individual's body condition. Before entering hibernation, animals need to store enough energy to last through the duration of their dormant period, possibly as long as the entire winter. Larger species become hyperphagic, eating a large amount of food and storing the energy
Climate of the British Isles persist for hours or even days in the winter and can pose a major hazard for drivers and aircraft. Fog is more common inland and on higher altitudes; mainly during winter and during the morning at times of high pressure. On occasions blocking anticyclones (high pressure systems) may move over the British Isles, which can persist for weeks or even months. The subsided, dry air often results in clear skies and few clouds, bringing frosty nights in winter and hot days in the summer, when some coastal areas can achieve almost maximum possible sunshine for periods of weeks. Rainfall varies