Perhaps one of the cutest bats you’ll find, the Brown long-eared bat usually roosts communally in roof and attic spaces. This one was part of a maternity colony of over 100 female bats hanging from the roof timbers of a church we recently surveyed. The building also had a Soprano pipistrelle roost one of our smallest bats weighing in at just 5-8 grams.
Bats are active after sunset and usually go to roost before sunrise. When surveying we use bat detectors and record their echolocation calls. They use high frequency calls to navigate and hone in on insects including midges. Their calls are inaudible to most people although teenagers can usually hear them. With some clever software we are able to distinguish the species of bat from the shape and frequency of the calls on the computer.
The three species of Pipistrelles found in Scotland have a peak frequency call at 38kHz, 45kHz and 55kHz - the latter higher pitch bat having been named the Soprano Pipistrelle. These 3 bats have a distinctive ‘hockey stick’ shaped call. The other species found in the north have a broader spectrum call and the Brown long-eared bat has a particularly quiet call which means in sometimes gets overlooked on surveys.
When the bats emerge from their roost they will often make a ‘b’ line to the nearest wood and their roosts are usually located close to foraging habitat. Emerging at sunset minimises the dangers from predators and with insects and moths emerging too they maximise their feeding opportunity before returning to roost before dawn to sleep it off.
During the day they are in a state of torpor where they will reduce their metabolic rate to conserve energy. Young bats born this year are now on the wing and will be busy putting on weight before the winter period. In Scotland bats hibernate from November to March/April a period of 6 months when there is very little for them to feed on. This is a pretty impressive feat for a mammal that can weigh as little as 5 grams.