Studying the vocalisations of dolphins provides an insight into their underwater behaviour whereas visual methods are normally restricted to surfacing behaviour. Apart from whistles, which seem to be produced in a social context, the sonar emissions of dolphins consist of pulsed signals used for different echolocation purposes. By analysing the pulse periodicity, frequency and spectral components of 'clicks' and relating these to video recorded surfacing behaviour it should be possible to extract characteristic patterns which indicate different kinds of dolphin behaviour. Almost all the pulsed emissions recorded during a series of 24 hour long intensive studies suggest behaviour related to foraging. These recordings provide unambiguous conditions where the environmental constraints can be observed and understood. Goodson and Datta (1992) found that recognisable patterns occurred in the repetition rate of the echolocation signals during these sequences. They partitioned these pulse sequences into 4 distinct phases. These sub-classifications have been further examined using an extended data set from the same source. Graphical and statistical analysis of six complete sequences, recorded immediately prior to a visually observed fish capture, allows a better definition of the presence of these foraging partitions. An additional fifth foraging phase was identified. The sequences could be partitioned into separate identifiable segments and characterised as foraging phases. Possibilities exist for automating this analysis for on-line use in the field as well as for the application of this analysis approach to behaviour types other than foraging.
K. Lucke and A.D. Goodson (1998). Off-line acoustic analysis of dolphin echolocation behaviour [abstract]. Bioacoustics 9(3): 226-227