Bats hibernate where they are less likely to be disturbed by light, noise and predators. Underground sites like caves, mines, cellars and service tunnels are ideal. Such sites are often referred to as hibernacula and they provide the optimum humidity and stable low temperature that bats require during their winter hibernation. Some bats also use underground roosts during the night in summer for feeding or for mating. Of all UK species, greater and lesser horseshoe bats rely most heavily on caves for roost sites.