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

Area of Science:

• Marine Biology
• Bioacoustics
• Animal Behavior

Background:

• Echolocating animals like bats and toothed whales use biosonar for navigation and foraging.
• Active control over sound emission properties (direction, rate, frequency, level) influences echo information.
• Dolphins and porpoises, both toothed whales, possess distinct biosonar signal characteristics.

Purpose of the Study:

• To investigate how bottlenose dolphins adjust echolocation behavior and movements when approaching and discriminating between objects.
• To compare dolphin performance with published data from harbor porpoises using identical tasks.
• To understand how species-specific biosonar signal properties influence echolocation strategies and discrimination abilities.

Main Methods:

• Two trained bottlenose dolphins performed discrimination tasks involving spheres of different materials.
• Dolphin sound production, head, and body movements were recorded during target approach.
• Behavioral data were compared with existing data from harbor porpoises under the same experimental paradigm.

Main Results:

• Both dolphins and porpoises displayed similar scanning behaviors and utilized a 'buzz' phase with short inter-click intervals during close-range approach.
• Bottlenose dolphins exhibited poorer discrimination performance compared to harbor porpoises.
• Porpoises demonstrated more refined close-range acoustic discrimination abilities than previously recognized.

Conclusions:

• Species-specific biosonar signal design significantly shapes echolocation information acquisition strategies.
• Harbor porpoises possess superior close-range acoustic discrimination capabilities compared to bottlenose dolphins.
• Differences in spectral and temporal properties of biosonar clicks likely contribute to observed performance disparities between the two species.