Scientists use three different kinds of evidence to study hearing in marine mammals: behavioral audiometry, which measures what a trained animal can perceive; auditory evoked potentials (AEPs), which measure electrical responses in the auditory system; and anatomical or mathematical models, which estimate hearing when direct tests are unavailable. These methods answer different questions, so a claim about a whale, dolphin, seal or other marine mammal should always identify the species and the method behind it.
What a marine-mammal hearing test actually measures
“Hearing” can refer to a perceptual threshold, a neural response, or an estimate derived from anatomy. A perceptual threshold is the quietest sound an animal signals that it detected under controlled conditions. A neural threshold is the sound level that produces a measurable electrical response in the auditory pathway. An estimate predicts likely sensitivity from physical evidence rather than testing the animal’s perception directly.
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- Behavioral audiometry: measures the animal’s reported detection of tones.
- Auditory evoked potentials: measure sound-evoked electrical activity from the auditory system.
- Anatomical and mathematical estimates: infer likely hearing from ear structure, vocalizations, playback responses and related physical data.
NOAA’s 2024 technical guidance places behavioral audiograms at the most representative, or sensitive, end of its evidence hierarchy because they measure perception itself. AEP results are valuable but are not interchangeable with behavioral thresholds. Modeled audiograms are useful where measurements are sparse, but they must be labeled as predictions or estimates rather than direct tests. NOAA’s 2024 technical guidance explains these distinctions.
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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchBehavioral audiometry: testing what the animal perceives
Behavioral audiometry is the closest equivalent to a conventional hearing test. Researchers present tones at selected frequencies and sound levels, then train an animal to signal whether it detected each sound. The signal might be a learned movement, a stationing response or another conditioned action; the exact behavior depends on the species and protocol.
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How a behavioral audiogram is made
- Condition the response. The animal learns that a particular action indicates “I heard the tone.” Researchers also teach a response for trials in which no tone is presented, helping distinguish detection from guessing.
- Present controlled sounds. The team delivers tones at known frequencies and levels through equipment appropriate for the animal and test environment. Background noise and the geometry of the sound field must be controlled as closely as possible.
- Vary the level around detection. For each frequency, tones are made softer or louder until the team can estimate the level at which the animal detects the sound reliably.
- Repeat and check performance. Repeated trials help identify inconsistent responses, changes in motivation and false alarms.
- Plot the thresholds. Detection levels across frequencies are assembled into an audiogram. The resulting curve shows where that individual was most and least sensitive under the test conditions.
What behavioral results can and cannot tell you
A behavioral audiogram answers a perceptual question: what sounds could this trained animal detect in this setup? It does not automatically describe every member of the species. Age, health, hearing damage, motivation, experience, water depth, equipment calibration and test geometry can all affect the result. Training is also a major requirement. An unconditioned wild animal normally cannot provide the repeated, reliable responses needed for a full behavioral audiogram.
Auditory evoked potentials: recording the response of the auditory system
Auditory evoked potentials, or AEPs, use electrodes to detect electrical activity produced when sound travels through the auditory pathway. Instead of asking an animal to make a learned choice, researchers present tones and look for a time-locked neural response in the recorded signal.
The field procedure
NOAA’s Alaska program describes a beluga procedure in which researchers place skin electrodes in soft silicone suction cups, present a subtle tone and measure the resulting brain response. In NOAA’s words: “We expose the whale to a subtle tone and measure its brain response with skin electrodes embedded in soft silicone suction cups.” The animal must still be accessible, the electrodes must maintain usable contact, and the team needs specialized stimulus, recording and analysis equipment. The method can be used with animals that have not received the extensive conditioning required for behavioral audiometry, which is particularly important during capture-and-release work. Details of the procedure are provided on NOAA Fisheries’ Alaska research page.
Why an AEP threshold is not a behavioral threshold
An AEP threshold is the lowest presented level at which the protocol can identify a repeatable neural response. A behavioral threshold is the lowest level at which the animal signals that it heard the sound. The two thresholds therefore measure different stages of the hearing process.
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NOAA reports that behavioral thresholds are consistently lower than AEP thresholds: an animal can often perceive a sound at a level below the point at which the recording system detects a sufficiently clear evoked response. There is no established correction that makes AEP results directly comparable with behavioral results across species and studies. A higher AEP threshold should not be described as proof that the animal cannot hear softer sounds in the behavioral sense.
Anatomical and mathematical estimates when direct tests are missing
Many marine-mammal species do not have direct behavioral or physiological audiometric measurements. Scientists can fill some gaps by modeling hearing from ear anatomy and other physical information. A model may use the structure and dimensions of the outer, middle and inner ear, known relationships among related animals, or acoustic characteristics of the species’ own signals.
Vocalizations and playback experiments can also contribute evidence. For example, researchers may examine the frequencies an animal produces or test whether it changes behavior when a sound is played back. Those observations can constrain a plausible hearing range, but they do not by themselves establish the quietest sound the animal can detect. NOAA’s technical review discusses these anatomical, vocalization-based and playback-based inferences in Marine Mammal Auditory Systems.
Model outputs should be labeled “estimated,” “predicted” or “modeled.” They are not direct audiograms from an individual animal. A modeled curve can support noise-impact analysis while still carrying more uncertainty than a measured behavioral or AEP curve.
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How the three approaches compare
| Method | Primary measurement | Direct test of an animal? | Training or access needed | Can its threshold be compared directly with another method? |
|---|---|---|---|---|
| Behavioral audiometry | Perceptual detection signaled by the animal | Yes, for the trained individual | Extensive conditioning and a controlled test setup | Not directly with AEP thresholds; they answer different questions |
| AEP | Electrical response generated by the auditory system | Yes, when the animal can be accessed and instrumented | Specialist electrodes, sound-delivery and recording equipment; less behavioral training | Not directly with behavioral thresholds; NOAA identifies no established universal correction |
| Anatomical or mathematical model | Predicted sensitivity from anatomy and other evidence | No; it is an inference | Physical data and assumptions about how structure relates to hearing | Only with explicit attention to the model’s assumptions and uncertainty |
The evidence does not support a standardized species-wide ranking of handling burden. A behavioral test generally demands more conditioning, while an AEP test demands physical access and specialist instrumentation; the practical difficulty depends on the species, setting and study design.
A wild-beluga example: AEP audiograms during capture and release
A 2018 study by T. Aran Mooney, Manuel Castellote, Lori Quakenbush, Roderick Hobbs, Eric Gaglione and Caroline Goertz used AEP methods during capture-release events to measure hearing in 26 wild beluga whales from Bristol Bay, Alaska. The results illustrate both the power and the limits of a field audiogram.
| Reported result | What it applies to |
|---|---|
| 26 wild beluga whales tested | The individuals examined in the Mooney et al. study, not every beluga population |
| Audiogram frequency span of 5.6–150 kHz | The frequencies tested in that study |
| Thresholds below 80 dB from 16 to 100 kHz | The sensitive range reported for the tested whales under the study protocol |
| 76% responded to at least 120 kHz | The proportion of those tested individuals showing an AEP response at that frequency or above |
| 30–70 dB variation among individuals | The substantial spread reported within this wild sample, increasing at higher frequencies |
The study is important because it demonstrates that AEPs can produce audiograms from wild animals encountered during a managed field event. It also shows why a single curve should not be treated as a universal species profile: individuals in the same population differed markedly, especially at higher frequencies. The source is Mooney et al., Journal of Experimental Biology (2018).
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Hydrophones, sonobuoys, fixed recorders and animal-attached acoustic tags passively listen to the environment. They can reveal which animals are present, which sounds they produce, when calls occur and what ambient noise they experience. NOAA uses passive acoustic monitoring for large-scale and year-round assessments of marine-mammal distribution and underwater noise.
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A recorder detecting a whale’s call does not establish the quietest sound that whale can hear. Detection means the instrument received energy from a sound source; it says nothing by itself about whether the animal perceived that sound, whether it could detect a quieter one, or how its sensitivity changes across frequency. NOAA’s description of a hearing test instead involves presenting a tone and recording a physiological response. The monitoring methods and their uses are described by NOAA’s Alaska program and its overview of recording and monitoring approaches at the same official page.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How hearing measurements support noise-impact decisions
Hearing data matter because human-made underwater and airborne sounds can affect marine mammals. NOAA Fisheries’ Updated Technical Guidance, finalized on October 24, 2024, provides thresholds for predicted onset of auditory injury and temporary threshold shifts for underwater and airborne sound sources. The guidance synthesizes available information to support management and impact assessment; it does not function as an individual animal’s audiogram.
In practice, analysts may combine measured or modeled hearing sensitivity with a sound source’s frequency content, level, duration and distance from animals. The result is a prediction of risk, not a direct observation of what a particular whale or seal heard. Exposure criteria therefore should not be quoted as if they were detection thresholds. The current guidance and related acoustic tools are available from NOAA Fisheries.
How to interpret a marine-mammal hearing claim
When reading a paper, report or environmental assessment, check four details before treating a number as a hearing limit:
- Species and population: confirm which animal was tested and whether the result came from captive, stranded, rehabilitated or wild individuals.
- Method: determine whether the number came from a behavioral audiogram, an AEP, a model, a playback response or passive acoustic monitoring.
- Frequency and level: note the tested frequency range and the units and calibration conditions attached to the threshold.
- Individual variation: look for the number of animals tested and the spread of results rather than relying on a single representative curve.
These checks prevent common category errors, such as calling a modeled audiogram a measurement, comparing an AEP threshold directly with a behavioral threshold, or treating a recorded call as evidence of hearing sensitivity.
Why direct measurements remain incomplete
Direct tests require either a trained animal or an animal that can be safely accessed and instrumented. Those requirements limit the number of species and individuals that can be studied, particularly for large, fast-moving or difficult-to-capture animals. As a result, NOAA continues to use modeled audiograms for groups with sparse direct evidence.
The absence of a published direct audiogram does not mean a species cannot hear a frequency. It means the available evidence may be indirect, limited to another species or based on a model with stated assumptions. The scientifically accurate wording is therefore “estimated hearing range” or “modeled sensitivity” unless a direct behavioral or physiological test supports a stronger claim.
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