The title of this article asks a deceptively simple question. The answer, however, is not that straightforward. Many researchers around the globe are working to figure out what sounds whales and dolphins (collectively referred to as cetaceans) can hear, the mechanisms by which they can hear those sounds, and the effects of those sounds on the animals' behavior and health. Here I will quantitatively summarize the data about what is currently known about hearing in these species. I will then touch on why that might matter in the context of human-made noise.
When we discuss what sounds any living being can hear, we are referring to the frequencies of sound that they can perceive. This is largely dictated by auditory anatomy. There are a variety of sizes and shapes of cetaceans, ranging from the massive baleen whales (mysticetes) to smaller toothed whales (odontocetes). The morphological differences between individuals in these two suborders could mean huge differences in the frequencies that these animals can hear.
Many dolphins emit high-frequency echolocation. It would be logical to assume that they can perceive these high frequency sounds that they produce. Likewise, most mysticetes produce low-frequency vocalizations, so we might assume that mysticetes are low-frequency species. But the key word here is assume. Maybe these animals can hear outside of their vocalization range as well. Obtaining the empirical data and numbers necessary to prove what frequencies they can hear has been very tricky. But, we do have some data, which is a good start.
Hearing is not only about the frequencies that can be heard, but also the intensities of sound necessary to hear at those frequencies. The standard measurement of hearing ability is an audiogram, or hearing threshold curve. Specifically, an audiogram is a graph of hearing threshold as a function of frequency. There are two major methods of measuring audiograms in cetaceans. The first is the behavioral method, in which a trained subject will visibly respond to auditory stimuli of varying intensity. The researcher will determine the intensity for each frequency that is just barely audible at each tested frequency, and together those data points will make up the audiogram curve. The other major method is the auditory evoked potential (AEP) method. Unlike the behavioral method, this method does not require a trained subject. Electrodes are used to measure brain activity in response to auditory stimuli. Both of these tests are non-invasive and safe for the subject.
This graph shows (almost) every cetacean audiogram that was experimentally measured. Hover over the individual curves to discover more about the experimental subject and source. Use the filter beside the graph to limit the data by species. For each species, the hearing range is extrapolated from the original data.
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[?] More information about audiogram shapes
[?] More information on data sources
For each species in the above figure, a frequency range of best hearing was calculated as the range of frequencies within 20 dB of the lowest threshold value (the peak frequency). In other words, sounds are easiest to perceive in this range of frequencies.
You will notice that only 20 cetacean species have experimentally-measured hearing threshold data. The number of total cetacean species varies depending on the source, but is generally around 90 species. Furthermore, all of these species are odontocetes. Mysticetes are more elusive and much less manageable for experimentation, making them difficult to study. However, three computational studies were able to estimate the hearing ranges of three different species of mysticete by using models rather than experimentation.
In the next figure, we can look closer at and compare those frequency ranges calculated above. This graph also includes the ranges (determined by the same 20 dB method) for the three mysticetes from each modeling paper: humpback whale, minke whale, and fin whale.
These are the ranges of best hearing for each cetacean species represented in the literature through experimentally measured thresholds or biophysical model results. Use the buttons above the graph to sort the data by different properties.
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[?] More information about modeling data
There are many sources of noise in the ocean, both natural and man-made (anthropogenic). Sources of anthropogenic noise include: shipping traffic, sonar, and airgun arrays used to detect oil and gas below the seafloor. Much of the man-made noise in the ocean is high-intensity and spans the gamut of frequencies, from infrasonic to ultrasonic. This can potentially interfere with hearing in all cetacean species.
As with most cases of working with data, this is a simplification. I feel it is my duty to address the shortcomings of this data analysis so that future iterations may give better estimations of marine mammal hearing. Some of the thresholds for species are wildly different, showing a likely dependence on the instrumentation and experimental standards that each study used. Furthermore, some of the animals may have been in poor health or exhibited hearing loss. Age may also be a factor: do infant cetaceans have different thresholds than adults? Some of the animals may exhibit age-related hearing loss.
Awbrey et al., 1988. Low-frequency underwater hearing sensitivity in belugas, Delphinapterus leucas. Journal of the Acoustical Society of America.
Bibikov, 1992. Auditory brainstem responses in the harbour porpoise (Phocoena phocoena). In: Marine Mammal Sensory Systems.
Brill et al., 2001. Assessment of dolphin (Tursiops truncatus) auditory sensitivity and hearing loss using jawphones. Journal of the Acoustical Society of America.
Castellote et al., 2014. Baseline hearing abilities and variability in wild beluga whales (Delphinapterus leucas). Journal of Experimental Biology.
Cook et al., 2006. Beaked whale auditory evoked potential hearing measurements. Journal of Comparative Physiology A.
Cranford and Krysl, 2015. Fin whale sound reception mechanisms: skull vibration enables low-frequency hearing. PLOS One.
Erbe and Farmer, 1998. Masked hearing thresholds of a beluga whale (Delphinapterus leucas) in icebreaker noise. Deep Sea Research Part II.
Finneran et al., 2005. Pure tone audiograms and possible aminoglycoside-induced hearing loss in belugas (Delphinapterus leucas). Journal of the Acoustical Society of America.
Finneran et al., 2007. Objective detection of bottlenose dolphin (Tursiops truncatus) steady-state auditory evoked potentials in response to AM/FM tones. Aquatic Mammals.
Finneran et al., 2009. Auditory evoked potentials in a stranded Gervais’ beaked whale (Mesoplodon europaeus). Journal of the Acoustical Society of America.
Greenhow et al., 2014. Hearing threshold measurements of five stranded short-finned pilot whales (Globicephala macrorhynchus). Journal of the Acoustical Society of America.
Hall and Johnson, 1972. Auditory thresholds of a killer whale Orcinus orca Linnaeus. Journal of the Acoustical Society of America.
Houser and Finneran, 2006. Variation in the hearing sensitivity of a dolphin population obtained through the use of evoked potential audiometry. Journal of the Acoustical Society of America.
Houser et al., 2001. A bandpass filter-bank model of auditory sensitivity in the humpback whale. Aquatic Mammals.
Houser et al., 2008. Evoked potential audiometry of 13 Pacific bottlenose dolphins (Tursiops truncatus gilli). Marine Mammal Science.
Jacobs and Hall, 1972. Auditory thresholds of a fresh water dolphin, Inia geoffrensis Blainville. Journal of the Acoustical Society of America.
Johnson et al., 1989. Masked tonal hearing thresholds in the beluga whale. Journal of the Acoustical Society of America.
Kastelein et al., 2002. Audiogram of a harbor porpoise (Phocoena phocoena) measured with narrow-band frequency-modulated signals. Journal of the Acoustical Society of America.
Kastelein et al., 2003. Audiogram of a striped dolphin (Stenella coeruleoalba). Journal of the Acoustical Society of America.
Kastelein et al., 2010. The effect of signal duration on the underwater detection thresholds of a harbor porpoise (Phocoena phocoena) for single frequency-modulated tonal signals between 0.25 and 160 kHz. Journal of the Acoustical Society of America.
Kastelein et al., 2013. Hearing frequency thresholds of a harbor porpoise (Phocoena phocoena) temporarily affected by a continuous 1.5kHz tone. Journal of the Acoustical Society of America.
Kastelein et al., 2015. Hearing thresholds of a harbor porpoise (Phocoena phocoena) for narrow-band sweeps (0.125-150 kHz). SEAMARCO final report.
Klishin et al., 2000. Hearing capabilities of a beluga whale, Delphinapterus leucas. Aquatic Mammals.
Li et al., 2012. Evoked-potential audiogram of an Indo-Pacific humpback dolphin (Sousa chinensis). Journal of Experimental Biology.
Ljungblad et al., 1982. Auditory thresholds of a captive Eastern Pacific bottle-nosed dolphin, Tursiops spp. Journal of the Acoustical Society of America.
Montie et al., 2011. Live CT imaging of sound reception anatomy and hearing measurements in the pygmy killer whale, Feresa attenuata. Journal of Experimental Biology.
Mooney et al., 2008. Hearing pathways and directional sensitivity of the beluga whale, Delphinapterus leucas. Journal of Experimental Marine Biology and Ecology.
Mooney et al., 2015. Hearing abilities and sound reception of broadband sounds in an adult Risso’s dolphin (Grampus griseus). Journal of Comparative Physiology A.
Nachtigall et al., 1995. Risso’s dolphin (Grampus griseus) hearing thresholds in Kaneohe Bay, Hawaii. In: Sensory Systems of Aquatic Mammals.
Nachtigall et al., 2005. Hearing measurements from a stranded infant Risso's dolphin, Grampus Griseus. Journal of Experimental Biology.
Nachtigall et al., 2008. Shipboard measurements of the hearing of the white-beaked dolphin Lagenorhynchus albirostris. Journal of Experimental Biology.
Pacini et al., 2010. Audiogram of a formerly stranded long-finned pilot whale ( Globicephala melas) measured using auditory evoked potentials. Journal of Experimental Biology.
Pacini et al., 2011. Audiogram of a stranded Blainville’s beaked whale (Mesoplodon densirostris) measured using auditory evoked potentials. Journal of Experimental Biology.
Popov and Klishin, 1998. EEG study of hearing in the common dolphin, Delphinus delphis. Aquatic Mammals.
Popov and Supin, 1990. Electrophysiological studies of hearing in some cetaceans and a manatee. In: Sensory Abilities of Cetaceans.
Popov et al., 1986. Evoked potentials of the auditory cortex of the porpoise, Phocoena phocoena. Journal of Comparative Physiology A.
Popov et al., 2005. Evoked-potential audiogram of the Yangtze finless porpoise Neophocaena phocaenoides asiaeorientalis (L). Journal of the Acoustical Society America.
Popov et al., 2007. Audiogram variability in normal bottlenose dolphins (Tursiops truncatus). Aquatic Mammals.
Popov et al., 2016. Auditory evoked potentials in the auditory system of a beluga whale Delphinapterus leucas to prolonged sound stimuli. Journal of the Acoustical Society of America.
Ridgway et al., 2001. Hearing and whistling in the deep sea: depth influences whistle spectra but does not attenuate hearing by white whales (Delphinapterus leucas) (Odontoceti, Cetacea). Journal of Experimental Biology.
Sauerland and Dehnhardt, 1998. Underwater audiogram of a tucuxi (Sotalia fluviatilis guianensis). Journal of the Acoustical Society of America.
Schlundt et al., 2011. Auditory evoked potentials in two short-finned pilot whales (Globicephala macrorhynchus). Journal of the Acoustical Society of America.
Supin and Popov, 2007. Improved techniques of evoked-potential audiometry in odontocetes. Aquatic Mammals.
Szymanski et al., 1999. Killer whale (Orcinus orca) hearing: auditory brainstorm response and behavioral audiograms. Journal of the Acoustical Society of America.
Thomas et al., 1988. Underwater audiogram of a false killer whale (Pseudorca crassidens). Journal of the Acoustical Society of America.
Tremel et al., 1998. Underwater hearing sensitivity of a Pacific white-sided dolphin, Lagenorhynchus obliquidens. Aquatic Mammals.
Tubelli et al., 2012. A prediction of the minke whale (Balaenoptera acutorostrata middle-ear transfer function. Journal of the Acoustical Society of America.
Wang et al., 1992. Auditory sensitivity of a Chinese river dolphin, Lipotes vexillifer. In: Marine Mammal Sensory Systems.
Yuen et al., 2005. Behavioral and auditory evoked potential audiograms of a false killer whale (Pseudorca crassidens). Journal of the Acoustical Society of America.