Abstract:
Describing the repertoire of sounds produced by wild cetaceans is necessary for understanding their
function, for acoustic population monitoring and for measuring the potential influence of
anthropogenic impact. Geographic variation in the types and parameters of sounds makes regional
assessment of vocal behaviour necessary. We describe the acoustic repertoire of a small population
of common bottlenose dolphins (Tursiops truncatus) inhabiting Walvis Bay, Namibia from
recordings made over 59 encounters (72 h) between 2009 and 2012. The characteristics of burst
pulse (BP) sounds, low-frequency narrow-band (LFN) sounds, brays, whistles and chirps are
described. The BP sounds identified were generated at 150–1050 pulses per second, and most were
short, lasting less than 1 s in duration. Bottlenose dolphins from Walvis Bay produce the lowest
frequency LFN sounds described for the species. Whistles ranged in frequency from 1.58 to 23.24
kHz, and the mean acoustic parameters were within the range of those described from other
geographic regions. Chirps were identified infrequently and usually as single occurrences. Although
several sound types were often produced in close temporal succession, we found little evidence of
stereotyped bray production, even during recordings of animals feeding. Our results demonstrate
geographic variation in both the characteristics and sound types used by bottlenose dolphins and
highlight the importance of regional data collection as a pre-curser to passive acoustic monitoring
programmes.
