SUMMARY Field recordings of harbour porpoises (Phocoena phocoena) were made in the inner Danish waters with a vertical array of three or four hydrophones. The back-calculated source level ranged from 178 to 205 dB re 1μPa pp @ 1 m with a mean source level of 191 dB re 1 μPa pp @ 1 m. The maximum source level was more than 30 dB above what has been measured from captive animals, while the spectral and temporal properties were comparable. Calculations based on the sonar equation indicate that harbour porpoises,using these high click intensities, should be capable of detecting fish and nets and should be detectable by porpoise detectors over significantly larger distances than had previously been assumed. Harbour porpoises in this study preferred a relatively constant inter-click interval of about 60 ms, but intervals up to 200 ms and down to 30 ms were also recorded.
SUMMARY Three Pipistrellus pygmaeus bats were trained to capture prey on the wing while flying in the laboratory. The bats' capture behaviour and capture success were determined and correlated with acoustic analyses of post-buzz echolocation signals. Three acoustic parameters revealed capture success: in case of success, post-buzz pauses (pbP) were longer, interpulse intervals (IPI) of the post-buzz signals were longer and, most notably, the spectra of the echolocation signals showed a number of notches that were absent after unsuccessful attempts. If the bats touched the prey without seizing it, pbP was significantly increased, but by less than was seen following a successful capture. Thus, acoustic recordings can be used to determine the outcome of a capture attempt with 72-75% correct using IPI or pbP, and with 78% correct using notches. Even more trials (>85%) were classified correctly by using the first canonical discriminant factor from principal component analysis combining the three parameters. Four types of prey were used, of 7-22 mm length and 7-240 mg mass. After successful captures, interpulse intervals, post-buzz pause and notches all depended on prey type, but not in a way that was systematically related to size, indicating that acoustic parameters cannot reveal prey size.