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Identify Big Bat Calls

The big bats (Noctule Nyctalus noctula, Leisler’s Bat Nyctalus leisleri and Serotine Eptesicus serotinus) have calls with lower peak frequencies than pipistrelles and, typically, with distinctive rhythms. However, they share the variability of pipistrelles’ calls and are very difficult (sometimes impossible) to distinguish from each other in woodland, when the peak frequency is raised and the distinctive rhythms tend to disappear.

* Three other species may sometimes appear to key out as Serotine, and close attention to detailed characteristics of the calls is needed to avoid misidentification. The species are:

Brown Long-Eared Bat – the typical calls of this species are quite different, but they occasionally make loud calls in which the FM sweep starts to level out into an almost constant frequency tail. The best check for this is to try to listen for a longer time to see if any of the more characteristic Brown Long-Eared Bat calls (see below) become detectable. Catching sight of the bat will help.

Barbastelle – the calls are never truly slaps, but may tend be rather prolonged clicks (tocks). Practice and careful listening enables them to be distinguished. The rhythm is also rather different, being reminiscent of impatient rapping on a door rather than the slightly slower and more syncopated rhythm of a Serotine. The peak frequency is above 32 kHz.

Greater Mouse-Eared Bat – so rare in Britain as to be scarcely worth considering. The sound of the calls is tocks, usually regular in rhythm, but occasionally erratic in the same pattern as a pipistrelle rather than the syncopated rhythm of a Serotine. The peak frequency is about 30 kHz.