Killer whale (Orcinus orca) hearing: auditory brainstem response and behavioral audiograms

Area of Science:

• Marine Biology
• Bioacoustics
• Auditory Neuroscience

Background:

• Killer whales (Orcinus orca) are toothed whales with complex vocalizations.
• Understanding their auditory capabilities is crucial for conservation and communication studies.
• Previous audiograms for Orcinus orca have varied, necessitating further investigation.

Purpose of the Study:

• To measure killer whale audiograms using both behavioral responses and auditory evoked potentials (AEPs).
• To compare the sensitivity and frequency range obtained from AEPs and behavioral methods.
• To determine the high-frequency hearing limit and most sensitive frequencies for Orcinus orca.

Main Methods:

• Two trained adult female killer whales were used for audiometric measurements.
• Behavioral audiograms were obtained through trained responses to auditory stimuli.
• Auditory evoked potentials (AEPs), specifically auditory brainstem response (ABR), were recorded.
• Tones ranging from 1 to 100 kHz were used to assess hearing thresholds.

Main Results:

• The mean auditory brainstem response (ABR) audiogram showed less sensitivity than behavioral audiograms by 12 dB.
• Threshold agreement between ABR and behavioral audiograms was best between 18-42 kHz (5 dB) and poorest at higher frequencies (60-100 kHz, 22 dB).
• The most sensitive frequency for Orcinus orca was 20 kHz (36 dB), aligning with echolocation click frequencies.
• Killer whales responded to tones up to 100 kHz, with one individual responding to 120 kHz.

Conclusions:

• Auditory brainstem response (ABR) audiometry is a viable method for estimating hearing ranges in toothed whales.
• Killer whale hearing sensitivity is highest around 20 kHz, matching their echolocation frequencies.
• The high-frequency hearing capabilities of killer whales extend beyond previously reported limits.