Greater Horseshoe bats in Autumn
As autumn approaches, bats are busy eating as much food as possible, this enables them to put on extra body fat see them through the coming winter, when no, or few insects are available. Bats spend less time in the warmer parts of a building, instead they choose to roost in the cooler areas where they lower their body temperature to save energy (called torpor).
By the end of October if it’s cold enough bats will start hibernating, most bats will move into nearby limestone caves that have high humidity and a stable temperature to protect them from frosts. However, they will wake occasionally, particularly on warm nights to go out to forage. This is a delicate balancing act; flying uses a lot of energy and if few insects are flying they’ll use more energy than they gain.