Our Bat populations have increased by 9% over the past few years, according to surveys for British Waterways, helped by increased protection and conservation measures. Cold winter’s also help, as Bats need consistently low temperatures to hibernate effectively. When they hibernate, their heart rate slows to a few beats a minute, meaning they burn less energy and survive better without seriously depleting their stored body weight. British Waterways compare our rivers and canals to supermarket aisles for insect-eating Bats. Here are a couple of our most commonly seen Bat: the small Pipistrelle. Conditions: a lovely blue-skied January day. Temperature: Max 7- Min 3C.