Field Observations of the Flexibility of the Acoustic Behaviour of the European Bat Nyctalus noctula (Schreber, 1774)

Abstract

The amount of variability in the sonar emissions of free flying European bats is scarcely known. This paper describes how the structure of the echolocation signals of Nyctalus noctula (Schreber, 1774) correlates to the height of flight, and to the varying density of obstacles in the flight path. Search pulses of bats flying close to the ground or near obstacles were short and of high frequency and large bandwidth. So far, these signals were not known to be typical for noctules. When the bats moved close to the ground in open areas, a succession of pulses suited to prey detection and of pulses suited to general orientation was found. The observed pulse structures are discussed with regard to their function to the acoustic orientation of the bat. A precision broadband ultrasound detector, developed by the author, was used to convert the signals to the audio range. A block diagram of the device is shown.