CCTV Enables the Discovery of New Barbastelle (Barbastella barbastellus) Vocalisations and Activity Patterns Near a Roost

Abstract

We monitored a barbastelle (Barbastella barbastellus) maternity roost for four months using a portable CCTV system, time synchronised with ultrasound recorders. We discovered three patterns of vocal activity not previously described. When barbastelles investigated the roost entrance, calls resembling the approach phase of echolocation were produced consisting of a group of 10 or more broadband pulses of low amplitude, not detected more than a few metres from the roost. The other two distinct vocal patterns were produced during swarming around the roost tree. The first consisted of broadband pulses which were similar to those in the approach pattern, but which tended to be produced in a dynamic group rather than a fixed pattern. They were of higher amplitude than the approach echolocation pulses and were considered to be swarming echolocation pulses. This pattern frequently morphed into sequences containing social calls with a quasi-constant frequency (QCF) tail of very high amplitude. These social calls were likely produced to warn approaching bats on a potential collision course, similar to calls previously described in other species as ‘honking’. In addition to these three vocalisations, standard echolocation pulses were emitted, as well as hooked calls presumably having a social context. These latter two vocalisations were less commonly recorded in our study. Pulse duration was shortest for approach echolocation and longest for the hooked social calls. Amplitude was lowest for approach echolocation and highest for swarming honking calls. The QCF tail in swarming honking was steeper than for swarming social calls. CCTV video evidence (by motion detection) proved invaluable for relating behaviour to call type.