Dolphin conditioned hearing attenuation in response to repetitive tones with increasing level

Area of Science:

• Marine Mammal Behavior
• Auditory Neuroscience
• Bioacoustics

Background:

• Toothed whales can decrease hearing sensitivity to loud sounds when warned.
• Conditions triggering this protective behavior are not fully understood.

Purpose of the Study:

• Investigate if dolphins reduce hearing sensitivity to intense tones without explicit warnings.
• Determine if dolphins can learn the timing of repetitive sounds to anticipate noise exposure.

Main Methods:

• Measured auditory brainstem responses (ABRs) in two bottlenose dolphins.
• Exposed dolphins to 40-kHz tones at increasing sound pressure levels (SPLs) and fixed intervals (20, 25, 29s).

Main Results:

• One dolphin showed consistent ABR attenuation above ~140-150 dB SPL at 20s intervals.
• ABR attenuation was inconsistent at longer intervals (25s, 29s).
• The second dolphin exhibited similar, though less pronounced, effects.

Conclusions:

• Dolphins can learn the timing of predictable, intense sounds.
• They may reduce hearing sensitivity to self-mitigate noise effects at high SPLs.