What sounds can animals hear?

Most animals, including marine mammals and fishes, hear best at the frequencies they produce and have varying sensitivity to sounds of different frequencies.

Many species differ in their ability to hear at any one frequency. Scientists and audiologists often display hearing abilities as a curve or audiogram, a graph of intensity vs. frequency. The figure below displays audiograms for several marine mammals and humans. You will notice that there are two y-axes. This is because we measure hearing in air (humans) differently than under water (marine mammals). Read here for more information on how hearing is measured, what humans can hear, or hearing threshold studies in marine animals.

Hearing curves for some marine mammals in water and a typical human in air. There are two sets of y-axes (vertical) because different reference pressures are used to measure sound in water (re 1 µPa; left axis) vs in air (re 20 µPa; right axis). Notice that the decibel values differ by 61.5 dB for the same value of intensity (watts/ m 2). The x-axis (horizontal) is the frequency of a sound on a logarithmic scale. (Figure courtesy of Darlene Ketten, WHOI).

All species of mysticetes (baleen whales),such as blue, fin, and humpback whales produce low frequency sounds. There are no direct measurements of hearing thresholds for baleen whales, but anatomical evidence and their vocalizations imply that all mysticetes hear well at low frequencies. Some species may be able to hear infrasonic or seismic signals (below 20 Hz). For example, measurements of the ears of thirteen North Atlantic right whales estimated that they can hear from 10 Hz to 22 kHz.

Direct studies have been performed on several odontocete (toothed whale) species including dolphins, beluga whales, and harbor porpoises. All species of toothed whales hear best at higher frequencies (10 kHz to 110 kHz). New technologies, including portable systems, are allowing scientists to measure an animal’s hearing in as little as 45 minutes. Studies can now be done on animals in the wild. For example, two white-beaked dolphins were captured while bow-riding off a fishing vessel. Their hearing sensitivities were measured onboard the vessel in a small plastic research tank, demonstrating the most sensitive high frequency hearing yet measured for any dolphin species. Similarly, an entire population of captive bottlenose dolphins was examined, including 42 individuals ranging in age from 4 to 47 years old. Scientists can see the change in hearing with age of this population.

Pinnipeds (seals, sea lions, and walruses) have increasing sensitivity from low to high frequencies. Several species of pinnipeds, including harbor seals and elephant seals, have been directly studied. Recent studies of harbor seals conducted in a pool specially designed for hearing studies (located in the Netherlands) have allowed scientists to more accurately measure hearing sensitivities. Because of the very low background noise, they discovered the lowest hearing sensitivity yet measured in harbor seals.

The average underwater hearing threshold in dB re 1 Pa, rms of the two study animals, shown as a line, and the underwater hearing thresholds found for harbor seals in previous studies: Møhl 1968, 500 ms; Terhune, 1988, 500 ms; Turnbull and Terhune, 1993, repeated signals, 50 ms, 10/s; Kastak and Schusterman, 1998, 500 ms; Southall et al., 2005, 500 ms. From: Kastelein, R. A., P. J. Wensveen, L. Hoek, W. C. Verboom, and J. M. Terhune. 2009. Underwater detection of tonal signals between 0.125 and 100 kHz by harbor seals (Phoca vitulina). Journal of the Acoustical Society of America, 125:1222-1229.

Studies on other marine species are just beginning to be conducted. A recent study using auditory evoked potential (AEP) techniques with sedated polar bears shows that they have good in-air hearing over a wide frequency range. They hear best between 11.2 kHz and 22.5 kHz^[1]Nachtigall, P. E., Supin, A. Y., Amundin, M., Roken, B., Moller, T., Mooney, T. A., … Yuen, M. (2007). Polar bear Ursus maritimus hearing measured with auditory evoked potentials. Journal of Experimental Biology, 210(7), 1116–1122. https://doi.org/10.1242/jeb.02734.

Individual, in-air audiograms for three polar bears in ambient noise conditions. Figure courtesy of Dr. Paul Nachtigall, Director, Marine Mammal Research Program, Hawai’i Institute of Marine Biology.

Most data regarding sea turtle, shark, and skate hearing come from studies using auditory brainstem responses (ABRs). From this work, scientists know that sea turtles can hear low to mid-frequency sounds underwater, but with poorer sensitivity than mammals.

Audiograms for the green turtle (Chelonia mydas; Cm), kemp’s ridley turtle (Lepidochelys kempi; Lk), and the loggerhead turtle (Caretta caretta; Cc). Audiograms are determined from Auditory Brainstem Responses (ABRs). Turtles do not hear well above 1,000 Hz or below 100Hz. Most sea turtles hear best between 200 and 700 Hz depending on the species and age of the turtle. From Ketten and Bartol (2005).

Sea turtles, in general, hear best between 200 and 750 Hz and do not respond well to sounds above 1,000 Hz (1 kHz). The graph shows that younger sea turtles of any species hear higher frequencies better than older turtles of the same species. As turtles grow older and larger, their hearing sensitivity shifts to lower frequencies.To determine the hearing capabilities in an adult green sea turtle, researchers obtained a behavioral audiogram for an older female green sea turtle, “Myrtle”, housed in the New England Aquarium’s Giant Tank exhibit. Based on her responses, it was concluded adult green sea turtles hear best between 200 Hz and 500 Hz.

Elasmobranchs, including sharks, skates, and rays, appear to respond best to low frequency sounds. The hearing of the little skate was tested using both behavioral and auditory brainstem response methods between 100 and 800 Hz. They were found to hear best at 200-300 Hz. Other species studied with ABRs show similar low-frequency sensitivity.

For more information about marine animals’ perception of sound, go to the sections on Marine Animal Sound Production and Marine Animal Sound Reception.

Additional Links on DOSITS

• Hearing Sensitivity Studies
• How does sound in air differ from sound in water?
• How is hearing measured?
• Sound Production
• Sound Reception
• What sounds can we hear?

References

• Casper, B. M., Lobel, P. S., & Yan, H. Y. (2003). The Hearing Sensitivity of the Little Skate, Raja erinacea: A Comparison of Two Methods. Environmental Biology of Fishes, 68(4), 371–379. https://doi.org/10.1023/B:EBFI.0000005750.93268.e4
• Houser, D. S., & Finneran, J. J. (2006). Variation in the hearing sensitivity of a dolphin population determined through the use of evoked potential audiometry. The Journal of the Acoustical Society of America, 120(6), 4090–4099. https://doi.org/10.1121/1.2357993
• Kastelein, R. A., Wensveen, P. J., Hoek, L., Verboom, W. C., & Terhune, J. M. (2009). Underwater detection of tonal signals between 0.125 and 100kHz by harbor seals (Phoca vitulina). The Journal of the Acoustical Society of America, 125(2), 1222–1229. https://doi.org/10.1121/1.3050283
• Ketten, D. R., & Bartol, S. M. (2005). Functional Measures of Sea Turtle Hearing. Woods Hole Oceanographic Institution: ONR Award No: N00014-02-1-0510.
• Nachtigall, P. E., Mooney, T. A., Taylor, K. A., Miller, L. A., Rasmussen, M. H., Akamatsu, T., … Vikingsson, G. A. (2008). Shipboard measurements of the hearing of the white-beaked dolphin Lagenorhynchus albirostris. Journal of Experimental Biology, 211(4), 642–647. https://doi.org/10.1242/jeb.014118
• Parks, S. E., Ketten, D. R., O’Malley, J. T., & Arruda, J. (2007). Anatomical predictions of hearing in the North Atlantic right whale. The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology, 290(6), 734–744. https://doi.org/10.1002/ar.20527
• Popov, V. V., Supin, A. Y., Pletenko, M. G., Tarakanov, M. B., Klishin, V. O., Bulgakova, T. N., & Rosanova, E. I. (2007). Audiogram variability in normal bottlenose dolphins (Tursiops truncatus). Aquatic Mammals, 33(1), 24–33. https://doi.org/10.1578/AM.33.1.2007.24
• Yamato, M., Ketten, D. R., Arruda, J., & Cramer, S. (2008). Biomechanical and structural modeling of hearing in baleen whales. Bioacoustics, 17(1–3), 100–102. https://doi.org/10.1080/09524622.2008.9753781