Bottlenose dolphin (Tursiops truncatus): Difference in the pattern of interpulse intervals

Abstract

When the echolocation detection abilities of a beluga whale and a bottlenose dolphin were tested on identical cylindrical targets and distances, they had interpulse interval (IPI) distributions which were different, while detection accuracy showed no significant difference. Bottlenose dolphin pulse trains show a predictable and systematic relationship between the distance to a detected target and time between echolocation pulses, thus permitting an inference of attending distance [R. H. Penner and J. Kadane, J. Acoust. Soc. Am. Suppl. I 68, S97 (1980)]. The beluga whale pulse trains contained, at all target distances, a first IPI component starting around 30 ms and increasing to 60 ms and a second IPI component between 200 to 220 ms which became more numerous as target distance increased. The transition zone between the first and second components contained very few interval counts. The interpulse intervals within the transition zone increased as target distance increased. If the bottlenose dolphin IPI patterns are accepted as models, and similar assumptions regarding attending distance are applied to the beluga whale pulse train, the picture is one of always scanning out to 30 m; followed by short scan out to 160 m. Subsequent target detection work using spheres instead of cylinders as targets, showed the same IPI distribution patterns for the beluga whale.