Burst-Pulse Sounds Recorded from White-Beaked Dolphins (<I>Lagenorhynchus albirostris</I>)

Abstract

Dolphin sounds are generally categorized as tonal whistles or pulsed clicks. Pulsed signals in dolphins are usually associated with echolocation; however, an increasing number of species have been found to produce burst-pulse signals, which may be used for communication. Groups of whitebeaked dolphins (Lagenorhynchus albirostris) were recorded near Halifax, Nova Scotia, Canada, with a hydrophone towed 25 m behind the boat at a depth of approximately 5 m and an M-Audio 24/96 digital recorder (16 bit, 96 kHz). During one 50-min encounter, 10 burst-pulse segments were recorded. Mean burst-pulse duration was 0.33 s (SD 0.17 s, range 0 3 to 0.60 s). Peaks from burstpulses were accurately identified with a MATLAB software-based signal detection and analysis program in nine segments of the recordings, totaling 521 individual peaks. Mean pulse rate was 719 Hz (SD 207 Hz, range 423 to 1,103 Hz), while the mean pulse period was 1.39 ms (SD 0.41 ms, range 0.91 to 2.36 ms). Mean peak frequency was 35.3 kHz (SD 11 kHz, range 1.5 to 46.5 kHz), and mean 3-dB bandwidth was 5.1 kHz (SD 1.4 kHz, range 3 to 10.5 kHz). Maximum received level was 159 dB re 1 μPa. The observed pulse rates were likely too rapid to be of use for echolocation. These sounds were made immediately before the group began actively swimming away from the boat at high speed, suggesting that they were used for communication as has been proposed for other species of dolphins. This is the first time burstpulses have been quantitatively analyzed for this genus of dolphin.