Target discrimination during active swimming in bottlenose dolphins (Tursiops truncatus)

Echolocating animals, such as bats and toothed whales, detect prey and other objects by emitting sound pulses and analyzing returning echoes. By adjusting direction, repetition rate, frequency content, and source level of their emissions, they actively control the information they obtain from returning echoes. We investigated how two trained bottlenose dolphins adjusted sound production as well as head, and body movements while approaching and discriminating between two spheres of different materials. We compared their performance with published data from harbor porpoises using the same paradigm. Harbor porpoise and bottlenose dolphin biosonar signals have different spectral and temporal properties that may affect their acoustic behavior and performance. If discrimination relies mainly on temporal cues, similar performance would be expected between the two species. If spectral cues dominate, porpoises should have an advantage. Both species exhibited comparable scanning behavior and a clear switch from longer inter-click intervals to short "buzz" phases during target approach. The dolphins' discrimination performance was poorer than that of porpoises. Our findings indicate that porpoises possess more refined close-range discrimination abilities than previously assumed and highlight how species-specific signal design shapes information acquisition strategies in echolocating mammals.