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Audiometric assessment of northern fur seals, Callorhinus ursinus
Abstract
Aerial and underwater audiograms for two young female northern fur seals (Callorhinus ursinus) and one young female California sea lion (Zalophus californianus) were obtained with the same procedure and apparatus. Callorhinus hears over a larger frequency range and is more sensitive to airborne sounds than Zalophus or any other pinniped thus far tested in the frequency range of 500 Hz to 32 kHz. Sensitivity of Callorhinus to waterborne pure tones, ranging from 2 to 28 kHz, is equal or superior to all other pinnipeds tested in this same frequency range. Like Zalophus, the upper frequency limit for underwater hearing (as defined by Masterton et al. 1969) in Callorhinus is about one-half octave lower than the three phocid species thus far tested. Callorhinus' upper frequency limit in air is about 36 kHz and under water it is about 40 kHz. Comparison of air and water audiograms shows Callorhinus is no exception to previous behavioral findings demonstrating that the „pinniped ear” is more suitable for hearing in water than in air. Similar to Zalophus and Phoca vitulina, Callorhinus shows an anomalous hearing loss at 4 kHz in air. The basis for this insensitivity to airborne sounds at 4kHz and not at lower or higher frequencies is presumably caused by specialized middle ear mechanisms matching impedance for waterborne sounds. Critical ratio curves for Callorhinus are similarly shaped to ones obtained for humans but are shifted upwards in frequency. Compared to all other marine mammals thus far evaluated, the critical ratios for Callorhinus are the smallest yet reported.
... For pnnpeds n water, behavoral measures of hearng are avalable for the northern fur seal (Callorhinus ursinus: Moore & Schusterman, 1987;Babushna et al., 1991), Calforna sea lon (Zalophus californianus: Schusterman et al., 1972;Moore & Schusterman, 1987;Kastak & Schusterman, 1998Southall et al., 2004), northern elephant seal (Mirounga angustirostris: Kastak & Schusterman, 1998, 1999Southall et al., 2004), Hawaan monk seal (Monachus schauinslandi: Thomas et al., 1990b), harp seal (Pagophilus groenlandicus: Terhune & Ronald, 1972), rnged seal (Phoca hispida: Terhune & Ronald, 1975), harbor seal (Møhl, 1967(Møhl, , 1968Terhune & Turnbull, 1995;Kastak & Schusterman, 1995Southall et al., 2004), and walrus (Odobenus rosmarus: Kastelen et al., 2002b). Rdgway & Joyce (1975) measured the gray seal's (Halichoerus grypus) underwater hearng usng evoked potental audometry. ...
... For pnnpeds n water, behavoral measures of hearng are avalable for the northern fur seal (Callorhinus ursinus: Moore & Schusterman, 1987;Babushna et al., 1991), Calforna sea lon (Zalophus californianus: Schusterman et al., 1972;Moore & Schusterman, 1987;Kastak & Schusterman, 1998Southall et al., 2004), northern elephant seal (Mirounga angustirostris: Kastak & Schusterman, 1998, 1999Southall et al., 2004), Hawaan monk seal (Monachus schauinslandi: Thomas et al., 1990b), harp seal (Pagophilus groenlandicus: Terhune & Ronald, 1972), rnged seal (Phoca hispida: Terhune & Ronald, 1975), harbor seal (Møhl, 1967(Møhl, , 1968Terhune & Turnbull, 1995;Kastak & Schusterman, 1995Southall et al., 2004), and walrus (Odobenus rosmarus: Kastelen et al., 2002b). Rdgway & Joyce (1975) measured the gray seal's (Halichoerus grypus) underwater hearng usng evoked potental audometry. ...
... For pnnpeds n ar, behavoral measures of hearng are avalable for the northern fur seal (Moore & Schusterman, 1987;Babushna et al., 1991), Calforna sea lon (Schusterman, 1974;Kastak & Schusterman, 1998;Kastak et al., 2004b), northern elephant seal (Kastak & Schusterman, 1998, 1999Kastak et al., 2004b), harp seal (Terhune & Ronald, 1971), and harbor seal (Møhl, 1968;Kastak & Schusterman, 1998;Kastak et al., 2004b). Aeral hearng n pnnpeds has also been measured usng evoked potental audometry n the gray seal (Rdgway & Joyce, 1975), Calforna sea lon (Bullock et al., 1971;Rdgway & Joyce, 1975;Rechmuth et al., 2007), harbor seal (Thorson et al., 1998;Wolsk et al., 2003;Rechmuth et al., 2007), and northern elephant seal Rechmuth et al., 2007). ...
... Underwater audiograms, and some in-air audiograms, have previously been constructed from sound-detection thresholds obtained for two otariid species, the California sea lion (Zalophus californianus, Schusterman et al. 1972;Schusterman 1974) and northern fur seal (Callorhinus ursinus, Moore and Schusterman 1987;Babushina et al. 1991). Auditory threshold data have also been published for several phocid species, including the harbor seal (Phoca vitulina, Møhl 1968;Turnbull and Terhune 1990;Terhune 1991), ringed seal (Phoca hispida, Terhune and Ronald 1975), harp seal (Phoca groenlandica, Ronald 1971, 1972) and Hawaiian monk seal (Monachus schauinslandi, Thomas et al. 1990). ...
... False alarm rates for all frequencies were below 12% and averaged 4% for in-air and underwater testing combined. The in-air audiogram is plotted in Fig. 2, in addition to audiograms from a phocid, the harbor seal (Møhl, 1968;Turnbull and Terhune 1990;Terhune 1991;Kastak and Schusterman 1998), and an otariid, the northern fur seal (Moore and Schusterman 1987;Babushina et al. 1991). Although the general shapes of the three audiograms are similar, the elephant seal is less sensitive than the other phocid by about 10-30 dB across the entire audible range. ...
... Underwater audiograms for the northern elephant seal (this study), harbor seal (Møhl 1968;Turnbull and Terhune 1990;Kastak and Schusterman 1998), and northern fur seal (Moore and Schusterman 1987). been obtained. ...
In-air and underwater sound detection thresholds were obtained for a female northern elephant seal (Mirounga angustirostris). Hearing sensitivity in air was generally poor, but was best for frequencies between 3.2 and 15 kHz, and showed greatest sensitivity at 6.3 kHz (43 dB re: 20 mu Pa). The upper frequency limit in air was approximately 20 kHz. The underwater audiogram is similar to those obtained from other phocids in that sensitivity was best between 3.2 and 45 kHz, with greatest sensitivity at 6.4 kHz (58 dB re: 1 mu Pa) and an upper frequency cutoff of approximately 55 kHz. The elephant seal was more sensitive to low frequencies (< 1 kHz) than other pinnipeds tested. Thresholds obtained in water were lower than those obtained in air (19 dB in terms of sound pressure, 52 dB in terms of sound intensity), indicating that the elephant seal is adapted for underwater hearing. The outer and middle ears of the elephant seal are modified relative to those of other phocids. These modifications are probably needed to cope with extreme static pressures related to deep diving, and are likely to confer relatively good auditory sensitivity under water.
... Underwater audiograms, and some in-air audiograms, have previously been constructed from sound-detection thresholds obtained for two otariid species, the California sea lion (Zalophus californianus, Schusterman et al. 1972;Schusterman 1974) and northern fur seal (Callorhinus ursinus, Moore and Schusterman 1987;Babushina et al. 1991). Auditory threshold data have also been published for several phocid species, including the harbor seal (Phoca vitulina, Møhl 1968;Turnbull and Terhune 1990;Terhune 1991), ringed seal (Phoca hispida, Terhune and Ronald 1975), harp seal (Phoca groenlandica, Ronald 1971, 1972) and Hawaiian monk seal (Monachus schauinslandi, Thomas et al. 1990). ...
... False alarm rates for all frequencies were below 12% and averaged 4% for in-air and underwater testing combined. The in-air audiogram is plotted in Fig. 2, in addition to audiograms from a phocid, the harbor seal (Møhl, 1968;Turnbull and Terhune 1990;Terhune 1991;Kastak and Schusterman 1998), and an otariid, the northern fur seal (Moore and Schusterman 1987;Babushina et al. 1991). Although the general shapes of the three audiograms are similar, the elephant seal is less sensitive than the other phocid by about 10-30 dB across the entire audible range. ...
... Underwater audiograms for the northern elephant seal (this study), harbor seal (Møhl 1968;Turnbull and Terhune 1990;Kastak and Schusterman 1998), and northern fur seal (Moore and Schusterman 1987). been obtained. ...
In-air and underwater sound detection thresholds were obtained for a female northern elephant seal (Mirounga angustirostris). Hearing sensitivity in air was generally poor, but was best for frequencies between 3.2 and 15 kHz, and showed greatest sensitivity at 6.3 kHz (43 dB re: 20 µPa). The upper frequency limit in air was approximately 20 kHz. The underwater audiogram is similar to those obtained from other phocids in that sensitivity was best between 3.2 and 45 kHz, with greatest sensitivity at 6.4 kHz (58 dB re: 1 µPa) and an upper frequency cutoff of approximately 55 kHz. The elephant seal was more sensitive to low frequencies (<1 kHz) than other pinnipeds tested. Thresholds obtained in water were lower than those obtained in air (19 dB in terms of sound pressure, 52 dB in terms of sound intensity), indicating that the elephant seal is adapted for underwater hearing. The outer and middle ears of the elephant seal are modified relative to those of other phocids. These modifications are probably needed to cope with extreme static pressures related to deep diving, and are likely to confer relatively good auditory sensitivity under water.
... Pure-tone hearing thresholds (masked and unmasked) are known for several species of pinnipeds (M8hl 1968;Ronald 197 1, 1972, 1975;Ridgway and Joyce 1975;Renouf 1980;Moore and Schusterman 1987;Terhune 1988Terhune , 1991Thomas et al. 1990;Turnbull and Terhune 1990). Information on hearing ability is important in evaluating the abilities of marine mammals to detect conspecific vocalizations, natural sounds, and industrial noises associated with shipping and oil and gas exploration. ...
... A 10-year-old male harbour seal was used as a subject. Using similar methods, this animal's masked and unmasked pure-tone hearing thresholds had been measured previously (Terhune 1988, 199 1 ;Turnbull and Terhune 1990) and are comparable to those of other pinnipeds tested (Mohl 1968;Ronald 197 1, 1972, 1975;Ridgway and Joyce 1975;Moore and Schusterman 1987). ...
... The occurrence of these dips likely does not explain all the variance in the data. Other studies have shown that between individuals of the same species, and even for the same animal, thresholds can vary between repeat measures (Moore and Schusterman 1987;Thomas et al. 1990;Terhune 199 1 ). These dips were also reported in a previous paper and occurred 10 dB above the calculated threshold (Terhune 1991). ...
Pure-tone hearing thresholds of a harbour seal (Phoca vitulina) were measured in air and underwater using behavioural psychophysical techniques. A 50-ms sinusoidal pulse was presented in both white-noise masked and unmasked situations at pulse repetition rates of 1, 2, 4, and 10/s. Test frequencies were 0.5, 1.0, 2.0, 4.0, and 8.0 kHz in air and 2.0, 4.0, 8.0, and 16.0 kHz underwater. Relative to 1 pulse/s, mean threshold shifts were −1, −3, and −5 dB at 2, 4, and 10 pulses/s, respectively. The threshold shifts from 1 to 10 pulses/s were significant (F = 12.457, df = 2,36, p < 0.001) and there was no difference in the threshold shifts between the masked and unmasked situations (F = 2.585; df = 1,50; p > 0.10). Broadband masking caused by meteorological or industrial sources will closely resemble the white-noise situation. At high calling rates, the numerous overlapping calls of some species (e.g., harp seal, Phoca groenlandica) present virtually continous "background noise" which also resembles the broadband white-noise masking situation. An implication of lower detection thresholds is that if a seal regularly repeats short vocalizations, the communication range of that call could be increased significantly (80% at 10 pulses/s). This could have important implications during the breeding season should storms or shipping noises occur or when some pinniped species become increasingly vocal and the background noise of conspecifics increases.
... The contour of the mean of the three session thresholds is shown by a solid black line. FIG. 2. Aerial audiograms for three species of otariid obtained using psychophysical methods: 1 Moore and Schusterman, 1987, California sea lion n1, northern fur seals n =2; 2 Babushina et al., 1991, northern fur seal n =1; 3 this study. tectionFig. ...
... One relevant application of ASSR methods is the detection of age-related hearing loss at the highfrequency end of the audiogram, which has been previously demonstrated in a California sea lion subject Schusterman et al., 2002 . Additionally, the underwater and aerial upperfrequency limits of hearing in otariids appear to occur at similar frequencies Schusterman et al., 1975; Moore and Schusterman, 1987; Babushina et al., 1991; Hemilä et al., 2006 , therefore, ASSR measurements of aerial hearing sensitivity may be of use in estimating otariid underwater audio- grams. ...
... It is conceivable that resonant properties of outer and/or middle ear structures could result in the " notches " of increased or decreased sensitivity in the mid-frequency region of otariid audiograms. The underwater audiograms of the otariids do not display such notches Schusterman et al., 1975; Moore and Schusterman, 1987; Babushina et al., 1991; Kastelein et al., 2005. This is congruent with the suggestion that these features are not cochlear in origin, but rather related to differences in the conformation of the outer and/or middle ear in aerial and underwater environments. ...
A within-subject comparison of auditory steady-state response (ASSR) and psychophysical measurements of aerial hearing sensitivity was conducted with an individual of the largest otariid species, the Steller sea lion. Psychophysical methods were used to obtain an unmasked aerial audiogram at 13 frequencies, spanning a range of 0.125-34 kHz. The subject had a hearing range (frequencies audible at 60 dB(rms) re 20 microPa) of about 0.250-30 kHz, and a region of best hearing sensitivity from 5-14.1 kHz. The psychophysical aerial audiogram of this Steller sea lion was remarkably similar to aerial audiograms previously obtained for California sea lions and northern fur seals, suggesting that the otariid pinnipeds form a functional hearing group. ASSR thresholds, measured at frequencies of 1, 2, 5, 10, 20, and 32 kHz, were elevated relative to corresponding psychophysical thresholds, ranging from +1 dB at 20 kHz, to +31 dB at 1 kHz. The ASSR audiogram accurately predicted the subject's high-frequency cutoff, and provided a reasonable estimate of hearing sensitivity at frequencies above 2 kHz. In testing situations where psychophysical methods are not possible, ASSR methods may provide an objective and efficient estimate of behavioral hearing sensitivity in otariid pinnipeds.
... Aerial hearing data for otariid pinnipeds (sea lions and fur seals) have demonstrated that these species are sensitive to aerial sound across a wide range of frequencies (Schusterman, 1974;Moore and Schusterman, 1987;Babushina et al., 1991;Kastak and Schusterman, 1998;Mulsow and Reichmuth, 2010), with absolute sensitivities similar to those of terrestrial carnivores (Fay, 1988). These findings are consistent with the importance of aerial vocalizations in otariid behaviors such as the maintenance of breeding territories (Peterson and Bartholomew, 1969;Fernandez-Juricic et al., 2001;Gwilliam et al., 2008) and the mutual recognition of mothers and pups (Trillmich, 1981;Gisiner and Schusterman, 1991;Insley et al., 2003). ...
... The shape of the Steller sea lion MRTF is generally similar to that of California sea lions (Mulsow and Reichmuth, 2007a;Mulsow and Reichmuth, 2007b) (this study) in terms of the range of modulation rates that elicit the highestamplitude ASSRs, and the highest rates for which an ASSR can be recorded. Similar temporal resolution in the Steller sea lion relative to the California sea lion is not surprising, considering the close phylogenetic relationship (see Heyning and Lento, 2002) and comparable aerial hearing capabilities in these two otariids (Schusterman, 1974;Moore and Schusterman, 1987;Mulsow and Reichmuth, 2010). These findings suggest that the SAM tone modulation rates similar to those used in this study will be an appropriate starting point for ASSR studies with other otariid species. ...
... The ASSR audiograms for most of the California and Steller sea lions are qualitatively similar to previously reported psychophysical audiograms for these species in that sensitivity typically increases with increasing frequency up to 10 kHz, and then decreases towards a cutoff between 20 and 32 kHz (Schusterman, 1974;Moore and Schusterman, 1987;Mulsow and Reichmuth, 2010). The similarity between the high-frequency hearing limits of the California sea lions from a wild population, the Steller sea lions housed permanently at VANAQ and the otariids previously tested using psychophysical methods suggests that the high-frequency hearing limit is a robust feature of audition in both captive and free-ranging populations. ...
Detection of aerial vocal signals by conspecifics is important in the reproductive behavior of the otariid pinnipeds. However, aerial hearing sensitivity measurements have only been obtained for a few otariid individuals that were trained to participate in behavioral experiments. In order to expand upon this small data set, auditory steady-state response (ASSR) methods were used to examine the aerial hearing sensitivity of Steller and California sea lions. Although ASSR thresholds were elevated relative to behavioral thresholds reported for otariids, the ASSR audiograms of the majority of individuals were similar to each other and to behavioral audiograms in terms of relative sensitivity. A marked reduction in sensitivity with increasing frequency regularly occurred between 16 and 32 kHz, indicating a consistent high-frequency cutoff. The reliability of the ASSR audiograms for both species suggests that behavioral aerial audiograms that exist for a few Steller and California sea lion individuals can be appropriately extrapolated to larger populations. The similarity of the ASSR audiograms among the Steller and California sea lions supports the notion that the otariid pinnipeds form a functional hearing group, with similar aerial hearing in terms of sensitivity and frequency range of hearing. [Work supported by ONR and NOAA Ocean Acoustics Program.].
... Am. 1303,2216-2228.; Moore, P.W.B., Schusterman, RJ., 1987. Audiometric assessment of northern fur seals, Callorhinus ursinus. ...
... Thirty years ago, the publication of the first seal behavioral audiogram (Møhl 1968a) changed the emphasis from anatomy to behavior for studying these systems. Additional audio grams followed representing both aerial and underwater thresholds of numerous seal and sea lion species including the harp seal, Phoca groenlandicus, (Terhune andRonald 1971,1972), the ringed seal, Phoca hispida, (Ronald and Terhune 1975), the California sea lion, Zalophus californianus, (Schusterman et al. 1972;Schusterman 1974), the northern fur seal, Callorhinus ursinus, (Moore and Schusterman 1987), the Hawaiian monk seal, Monachus schauinslandi, (Thomas et al. 1990), the Pacific walrus, Odobenus rosmarus, (Kastelein et al. 1996), and the northern elephant seal, Mirounga angustirostris, (Kastak and Schusterman 1997). Recent papers (Kastak and Schusterman 1998;) have used behavioral techniques to show significant hearing differences between largely aquatic seals (phocids) and largely terrestrial sea lions (otariids). ...
... There is a relatively large body of behavioral work on their hearing abilties (Møhl 1968a(Møhl , 1968bSchusterman et al. 1972;Schusterman 1974;Moore and Schusterman 1987;Schusterman 1998, 1999;Southall et al. 2000). In addition, specimens for dissection are not generally difficult to obtain. ...
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 2001 Pinniped (seal and sea lion) auditory systems operate in two acoustically distinct environments, air and water. Piniped species differ in how much time they typically spend in water. They therefore offer an exceptional opportunity to investigate aquatic versus terrestrial hearing mechanisms. The Otariidae (sea lions and fur seals) generally divide their time evenly between land and water and have several adaptations; e.g. external pinnae, related to this lifestyle. Phocidae (true seals) spend the majority of their time in water; they lack external pinnae and have well developed ear canal valves. Differences in hearing ranges and sensitivities have been reported recently for members of both of these familes (Kastak, D., Schusterman, RJ., 1998. Low frequency amphibious hearing in pinnipeds. J. Acoust. Soc. Am. 1303,2216- 2228.; Moore, P.W.B., Schusterman, RJ., 1987. Audiometric assessment of northern fur seals, Callorhinus ursinus. Mar. Mamm. Sci. 3,31-53.). In this project, the ear anatomy of three species of pinnipeds: an otariid, the California sea lion (Zalophus californianus), and two phocids, the northern elephant seal (Mirounga angustirostris) and the harbor seal (Phoca vitulina), was examined using computerized tomography (CT scans) and gross dissection. Thee-dimensional reconstructions of the heads and ears from CT data were used to determine interaural dimensions and ossicular chain morphometrics. Ossicular weights and densities were measured conventionally. Results strongly support a canalcentric system for pinniped sound reception and localization. Further, true seals show adaptations for aquatic high frequency specialization. I was supported by an NDSEG fellowship from ONR.
... In the past relatively few studies were carried out in the field of marine mammal hearing perception. A summary is: determination of odontocete audiograms, among which low-frequency (LF) hearing of 6 species (bottlenose dolphin, beluga, false killer whale, risso's dolphin, river dolphin; white-sided dolphin, killer whale; Andersen (1970a), Hall & Johnson (1972), Johnson (1967Johnson ( , 1968a, White et al. (1978), Thomas et al. (1987), Awbrey et al. (1988), Johnson et al. (1989), Au (1993), Nachtigall et al. (1995), Jacobs & Hall (1972), Tremel et al. (1998) ), Szymanski et al. (1999) and influence of depth/pressure on beluga hearing (Ridgway et al. (1997b)) determination of pinniped and manatee audiograms, among which LF hearing of 6 species (fur seal, ringed seal, harbour seal, sea lion, elephant seal, west-indian manatee; Mhl (1968), Schusterman et al. (1972), Moore & Schusterman (1987), Terhune & Ronald (1972, 1975, Terhune (1988Terhune ( , 1991, Babushina et al. (1991), Turnbull & Terhune (1993), Kastak & Schusterman (1995), Gerstein et al. (1999) determination of in-air audiograms (walrus, harbour porpoise; Kastelein et al. (1993Kastelein et al. ( , 1996Kastelein et al. ( , 1997a; sea lion, harbour seal, elephant seal; Kastak & Schusterman (1998)) determination of odontocete and pinniped Temporary Threshold Shift (bottlenose dolphin, beluga, harbour and elephant seal, sea lion: Ridgway et al. (1997a);Carder et al. (1998);Schlundt et al. (2000); Kastak et al. (1999)) determination of aversive behavioural effects (Verboom (1991), Green (1994), Richardson et al. (1995), Gordon & Moscrop (1996), Todd et al. (1996), Kastelein et al. (1997b), Taylor et al. (1997), Terhune & Verboom (1999)) estimation of baleen and beaked whale hearing from anatomy (Ketten (1992) remote techniques, such as Auditory Evoked Potential measurements (Ridgway & Joyce (1974), Popov et al. (1986), Popov & Supin (1990), Bibikov (1992), Szymanski et al. (1999)) detailed investigations, such as critical bandwidth/ratio, influence masking, signal duration, beam patterns, etc. (Johnson (1968), Terhune & Ronald (1975), Johnson et al. (1989), Au & Moore (1990), Turnbull & Terhune (1990), Thomas et al. (1990c), Terhune (1988Terhune ( , 1991, Au (1993), Turnbull & Terhune (1993)). ...
... For five species of the hair seals and two species of the eared seals, underwater audiograms have been determined: hair seals: harbour seal (Mhl (1968); Terhune (1988); Turnbull & Terhune (1993); Kastak & Schusterman (1995); ringed seal (Terhune & Ronald (1975)); harp seal (Terhune & Ronald (1972)); elephant seal (Kastak & Schusterman (1998)); grey seal (Ridgway & Joyce (1974) evoked potential); for observations, see Figure 4. eared seals: fur seal (Moore & Schusterman (1987); Babushina et al. (1991)); sea lion (Schusterman et al. (1972); Kastak & Schusterman (1995); for observations, see Figure 5. Masking noise influenced some of these observations, so the guideline audiograms have been taken at 'the sensitive side' of the observations. Evoked potential observations (grey seals) have been left out of consideration in the determination of the guideline audiograms. ...
World wide a concern is emerging about the effects of anthropogenic noise in the marine environment. At present most concern lies with marine mammals (cetaceans and pinnipeds), simply because of the fact that from these animals knowledge of the physiological effects of anthropogenic noise on the auditory system is more developed than from ‘lower’ animal species. However, knowledge around acoustic disturbance and/or injury of marine mammals is still very limited, as well as detailed information on marine mammal hearing systems. Intense sounds can have negative physiological, hearing and behavioural effects on marine animals in general. For marine mammals sound is very important as a means for communication, forage and as source of environmental information (danger!). Marine mammals are threatened by many causes and are of greatest concern due to, for certain species, on-going depletion. It will be clear that mitigation of anthropogenic noise is at least recommendable to protect marine life.
... Northern fur seal (Callorhinus ursinus) Babushina et al. (1991) 0.1-25 kHz (behavioural, air) 0.5-40 kHz (behavioural, water) Moore and Schusterman (1987) 0.5-32 kHz (behavioural, air) 0.5-42 kHz (behavioural, water) Steller sea lion (Eumetopias jubatus) Kastelein et al. (2005b) 0.5-32 kHz (behavioural, water) Mulsow et al. (2011b) 1-32 kHz (physiological, air) Mulsow and Reichmuth (2010) 1-32 kHz (physiological, air) 0.125-34 kHz (behavioural, air) California sea lion (Zalophus californianus) Reichmuth et al. (2013) 0.1-32.5 kHz (behavioural, air) 0.1-43.054 kHz (behavioural, water) Finneran et al. (2011) 0.5-32 kHz (physiological, air) Kastak and Schusterman (1998) 0.1-6.4 ...
... kHz (behavioural, air) 0.075-6.4 kHz (behavioural, water) Kastak and Schusterman (2002) 2.5-35 kHz (behavioural, water) Moore and Schusterman (1987) 1-32 kHz (behavioural, air) Mulsow et al. (2011a) 2-32 kHz (physiological, air) Mulsow et al. (2012a) 1-38 kHz (behavioural, water) Mulsow et al. (2014) 0.5-32 kHz (physiological, air) Mulsow et al. (2011b) 0.5-32 kHz (physiological, air) Schusterman (1974) 4-32 kHz (behavioural, air) Schusterman et al. (1972) 0.25-64 kHz (behavioural, water) 6.4-37.2 kHz (behavioural, water) Cunningham et al. (2014a) 69 kHz (behavioural, water) ...
Underwater noise, whether of natural or anthropogenic origin, has the ability to interfere with the way in which marine mammals receive acoustic signals (i.e., for communication, social interaction, foraging, navigation, etc.). This phenomenon, termed auditory masking, has been well studied in humans and terrestrial vertebrates (in particular birds), but less so in marine mammals. Anthropogenic underwater noise seems to be increasing in parts of the world's oceans and concerns about associated bioacoustic effects, including masking, are growing. In this article, we review our understanding of masking in marine mammals, summarise data on marine mammal hearing as they relate to masking (including audiograms, critical ratios, critical bandwidths, and auditory integration times), discuss masking release processes of receivers (including comodulation masking release and spatial release from masking) and anti-masking strategies of signalers (e.g. Lombard effect), and set a research framework for improved assessment of potential masking in marine mammals.
... Clear differences in basilar membrane size and morphology exist within odontocetes (Ketten 1992a); however, despite large differences in ear morphology (Ketten 1992b), functional head size (Heffner and Heffner 2008), and frequency sensitivity (see NOAA Fisheries 2018), critical ratios for toothed whales species are remarkably similar (Fig. 3A). Among pinnipeds, critical ratio measurements are available for nine species: Callorhinus ursinus (Moore and Schusterman, 1987), Erignathus barbatus (Sills et al. 2020), Mirounga angustirostris (Southall et al. 2000(Southall et al. , 2003, Neomonachus schauinslandi (Ruscher et al. 2021), Pagophilus groenlandicus (Terhune and Ronald 1971), Phoca largha (Sills et al. 2014), Phoca vitulina (Renouf 1980;Southall et al. 2000Southall et al. , 2003Terhune 1991;Turnbull 1994;Turnbull andTerhune 1990, 1993), Pusa hispida (Sills et al. 2015;Terhune and Ronald 1975), and Zalophus californianus (Southall et al. 2000;. Critical ratios measured for seals and sea lions (Fig. 3B) are consistently low across a wide range of frequencies relative to many terrestrial mammals (Fay 1988). ...
Anthropogenic noise is an increasing threat to marine mammals that rely on sound for communication, navigation, detecting prey and predators, and finding mates. Auditory masking is one consequence of anthropogenic noise, the study of which is approached from multiple disciplines including field investigations of animal behavior, noise characterization from in-situ recordings, computational modeling of communication space, and hearing experiments conducted in the laboratory. This paper focuses on laboratory hearing experiments applying psychophysical methods, with an emphasis on the mechanisms that govern auditory masking. Topics include tone detection in simple, complex, and natural noise; mechanisms for comodulation masking release and other forms of release from masking; the role of temporal resolution in auditory masking; and energetic vs informational masking.
... In the past relatively few studies were carried out in the field of marine mammal hearing perception. A summary is: determination of odontocete audiograms, among which LF hearing of 6 species (bottlenose dolphin, beluga, false killer whale, risso's dolphin, river dolphin; white-sided dolphin, killer whale; Andersen (1970a), Hall & Johnson (1972, Johnson (1967Johnson ( , 1968, White et al. (1978), Thomas et al. (1987), Awbrey et al. (1988), Johnson et al. (1989), Au (1993), Nachtigall (1995), Jacobs & Hall (1972), Tremel et al. (1998 ), Szymanski et al. (1999) and influence of depth/pressure on beluga hearing (Ridgway et al. (1997b)) determination of pinniped and manatee audiograms, among which LF hearing of 4 species (fur seal, ringed seal, harbour seal, west-indian manatee; Moore & Schusterman (1987), Terhune & Ronald (1975), Terhune (1991), Turnbull & Terhune (1993), Gerstein et al. (1999) determination of in-air audiograms (walrus, harbour porpoise; Kastelein et al. (1993Kastelein et al. ( , 1996Kastelein et al. ( , 1997a; sea lion, harbour seal, elephant seal; Kastak & Schusterman (1998)) determination of odontocete Temporary Threshold Shift (first results bottlenose dolphins: Ridgway et al. (1997a), Carder et al. (1998) determination of aversive behavioural effects (Verboom (1991), Green (1994), Richardson (1995), Gordon & Moscrop (1996), Todd et al. (1996, Kastelein et al. (1997b), Taylor et al. (1997, Terhune & Verboom (1999)) estimation of baleen and beaked whale hearing from anatomy (Ketten (1992) remote techniques, such as Auditory Evoked Potential measurements (Popov et al. (1986), Popov & Supin (1990), Bibikov (1992), Szymanski et al. (1999)) detail investigations, such as critical bandwidth/ratio, influence masking, signal duration, beam patterns, etc. (Johnson (1968), Terhune & Ronald (1975), Johnson et al. (1989), Au & Moore (1990), Turnbull & Terhune (1990, Thomas et al. (1990), Terhune (1988, 1991, Au (1993), Turnbull & Terhune (1993). ...
The TNO Institute of Applied Physics (TNO-TPD) carries out a study on possible negative effects of intense low-frequency (LF) sounds on marine life. One of the reasons for this study is an article published in ‘Nature’ (5 March 1998) “Does acoustic testing strand whales?”, in which LF sound was hypothesised to be the cause of whale strandings in Greece. The present part of the TNO-TPD study concerns the acoustic influence of LF sounds on cetaceans , with emphasis on possible negative/damaging effects on cetacean hearing. In future also LF sound effects on pinnipeds will be studied.
... Data on the critical bandwidth or the critical ratio of the harbour porpoise hearing system and for other cetaceans are scarce. An estimation of the harbour porpoise critical bandwidth was made (see Figure 4) based on available data [5] [6] [7]; for pinnipeds: [8] [9] [10], as well as from relevant human data. ...
... The aerial auditory capabilities of 4 pinniped species (Zalophus californianus, Callorhinus ursinus, Phoca vitulina, and Phoca groenlandica) were summarized by Moore and Schusterman (1987). However, comparison of the auditory thresholds of different species is only valid within certain limits because of discrepancies in ambient noise level, equipment and measuring technique, methodology and definition of the thresholds. ...
The aerial hearing of a 10-year-old male Pacific walrus was tested from 0.125 to 8 kHz, the frequency range covering the ranges of human speech, industrial noise and most Walrus vocalizations. Two behavioral audiometric test methods were used in a study area with a fluctuating background noise level of 52 ± 4 dB(A) re 20 mPa. The go/no-go paradigm was used in both tests. 1. Headphones were used to investigate the aerial hearing sensitivity of each ear for pure tones of 0.125, 0.25, 0.5, 1.0, 2.0, 4.0 and 8.0 kHz. A modification of the descending staircase psychometric technique was used (Levitt, 1970). Both ears were equally sensitive. Between 0.125 and 0.25 kHz, the detection thresholds dropped from 105 dB to 80 dB and between 0.25 and 2.0 kHz from 80 to 60 dB re 20 mPa. Between 2.0 kHz and 8.0 kHz the thresholds increased to around 65 dB. The hearing thresholds obtained with headphones suggest very poor hearing in this Walrus compared to other tested pinnipeds. However, this does not agree with the day-today experiences at the Harderwijk Marine Mammal Park where many behavioral commands are given orally to the study animal. Maybe the outer ear canal was closed off by the auricular muscles due to the presence of headphones. 2. "Free field" (not a true free field in the acoustical sense of the word, because the room was echoic and not sound isolated) measurements were carried out on the same Walrus, in which the aerial hearing sensitivity was tested for 2 types of sound signals (frequency modulated tones and filtered band noise) with centre frequencies of 0.25, 0.5, 1.0, 2.0 and 4.0 kHz. The Walrus responded to signals that were 3 to 13 dB above the 1/3-octave background noise levels, which suggests that the hearing thresholds reported were masked thresholds. The same "free field" hearing test was done with a human with his head in the same location as the Walrus's. The human heard the signals between 0 and 12 dB below the lowest level of the background noise. Comparison of the Walrus and the human hearing curves suggests that the Walrus's hearing is less acute than that of the human for the tested frequencies. Tests were conducted to determine which stimulus instigates the closure of the external auditory meatal orifice. The stimulus that causes closure was not discovered, but certain possibilities were ruled out. Closure was not triggered by pressure on the outer ear canal or mechanical stimulation of the skin immediately around the meatal orifice. Perhaps the change in sound field when diving, instigates closure. It is also possible that closure is under voluntary control.
... Data on the critical bandwidth or the critical ratio of the harbour porpoise hearing system and for other cetaceans are scarce. An estimation of the harbour porpoise critical bandwidth was made (see Figure 4) based on available data [5] [6] [7]; for pinnipeds: [8] [9] [10], as well as from relevant human data. ...
The number of aquaculture facilities around the world using acoustic harassment devices (AHDs) in attempts to deter seals from approaching fish pens has increased, yet our understanding of the effects of these devices on both target and non-target species, in the short and long term, is still largely incomplete. Recently developed AHDs typically produce sounds with a high acoustic source level (circa 200 dB re 1µPa at 1m ) and medium to high frequencies (10-25 kHz and up to 40 kHz) which pinnipeds and some cetaceans are particularly sensitive to.
There are growing concerns about the behavioural and physical impacts of such AHDs on both target species (generally pinnipeds) and on non-target species (odontocete cetaceans, some fish and potentially invertebrates as well) in the vicinity of operating devices. Preliminary investigations from the west coast of Canada appear to validate at least some of these concerns, as significant decreases in harbour porpoise (Phocoena phocoena) abundance within 3.5 km of an active AHD have been documented.
Here we estimate areas within which harbour porpoises are likely to perceive and be affected by AHD sounds based on calculations incorporating the source levels and attenuation characteristics of three particular models of AHD. These results indicate that some AHD sounds may be broadcast over considerable distances -- up to about 12 km before dissipating to background noise levels -- and may effectively reduce the availability of marine habitat to a number of different species.
... When compared with available data for ice-living seals, these ringed seal audiogramsalong with recent data for spotted seals (Sills et al., 2014)show significantly better sensitivity to airborne sounds than measured previously for one harp seal (Terhune and Ronald, 1971). While others have suggested that the harp seal thresholds were elevated as a result of noise (Watkins and Wartzok, 1985;Moore and Schusterman, 1987), the reported ambient noise levels and CRs (Terhune and Ronald, 1971) suggest that masking was not a relevant factor. We conducted a separate experiment to reconcile these differences in reported hearing sensitivity between studies and species. ...
Ringed seals are semi-aquatic marine mammals with a circumpolar Arctic distribution. In this study, we investigate the amphibious hearing capabilities of ringed seals to provide auditory profiles for this species across the full range of hearing. Using psychophysical methods with two trained ringed seals, detection thresholds for narrowband signals were measured under quiet, carefully controlled environmental conditions to generate aerial and underwater audiograms. Masked underwater thresholds were measured in the presence of octave-band noise to determine critical ratios. Results indicate that ringed seals possess hearing abilities comparable to those of spotted and harbor seals, and considerably better than previously reported for ringed and harp seals. Best sensitivity was 49 dB re 1 µPa (12.8 kHz) in water, and -12 dB re 20 µPa (4.5 kHz) in air, rivaling the acute hearing abilities of some fully aquatic and terrestrial species in their respective media. Critical ratio measurements ranged from 14 dB at 0.1 kHz to 31 dB at 25.6 kHz, suggesting that ringed seals-like other true seals-can efficiently extract signals from background noise across a broad range of frequencies. The work described herein extends similar research on amphibious hearing in spotted seals, the results of which were recently published in this journal [Sills et al., J. Exp. Biol., 217, 726-734 (2014)]. These parallel studies enhance our knowledge of the auditory capabilities of ice-living seals, and inform effective management strategies for these and related species in a rapidly changing Arctic environment.
© 2015. Published by The Company of Biologists Ltd.
... In the absence of any auditory data for sea otters, Finneran & Jenkins (2012) proposed that sea otters should be classified with otariid pinnipeds (sea lions and fur seals) for this purpose. The similar aerial hearing ranges for the sea otters measured herein, as compared to available data for otariids (see Moore & Schusterman, 1987;Mulsow & Reichmuth, 2010;Mulsow et al., 2011;Reichmuth et al., 2013), provides the first experimental support for this grouping. It remains to be seen whether sea otters, like otariids, will exhibit hearing ranges under water that are similar to those measured in air. ...
The sea otter (Enhydra lutris) is an amphibious marine mammal that is vulnerable to coastal anthropogenic disturbance. Effective management of noise-generating activities within sea otter habitats requires information about hearing that is presently unavailable for this species. As an initial step toward describing the auditory capabilities of sea otters, we used a controlled exposure approach to conservatively estimate the aerial frequency range of hearing in four captive individuals. The study was designed to determine which frequencies were audible to each animal rather than to quantify auditory sensitivity. To this end, the sea otters were intermittently exposed to relatively high-amplitude tones between 0.063 and 45.3 kHz-and to blank "control" events-during periods of sustained rest. Positive responses to both the sound exposure trials and the control trials were scored by experimentally blind observers and used to determine statistically reliable detections at each frequency. The widest confirmed hearing range measured for the sea otters was 0.125 to 32 kHz. Our results indicate that sea otters can detect a broad range of airborne sounds, similar to many terrestrial carnivores that have been studied. These are the first hearing measurements obtained for this species, and the results are relevant to improving understanding of sea otter acoustic communication, evolutionary biology, and behavioral ecology, as well as in supporting ongoing conservation efforts. This method can be adapted to examine the acoustic detection capabilities of species for which little data are available and for which conventional audiometry may prove challenging.
... Otariid hearing limits are estimated to be 100 Hz -35 kHz and 100 Hz -50 kHz in air and water, respectively (Babushina et al., 1991;Kastak and Schusterman, 1998;Kastelein et al., 2005b;Moore and Schusterman, 1987;Mulsow and Reichmuth, 2007;Mulsow et al., 2011a;Mulsow et al., 2011b;Schusterman et al., 1972). ...
... Existing harp seal thresholds (Terhune and Ronald, 1971) -the only aerial data available for ice seals -are substantially elevated across the frequency range of hearing relative to the thresholds measured in this study. While some have suggested that these thresholds were elevated by background noise (Moore and Schusterman, 1987;Watkins and Wartzok, 1985), they were more likely influenced by methodological factors. During testing, the harp seal's head was submerged immediately prior to each trial, which may have impeded the aerial sound conduction pathway (Terhune and Ronald, 1971). ...
Spotted seals (Phoca largha) inhabit Arctic regions that are facing both rapid climate change and increasing industrialization. While little is known about their sensory capabilities, available knowledge suggests that spotted seals and other ice seals use sound to obtain information from the surrounding environment. To quantitatively assess their auditory capabilities, the hearing of two young spotted seals was tested using a psychophysical paradigm. Absolute detection thresholds for tonal sounds were measured in air and under water over the frequency range of hearing, and critical ratios were determined using octave-band masking noise in both media. The behavioral audiograms show a range of best sensitivity spanning four octaves in air, from approximately 0.6 to 11 kHz. The range of sensitive hearing extends across seven octaves in water, with lowest thresholds between 0.3 and 56 kHz. Critical ratio measurements were similar in air and water and increased monotonically from 12 dB at 0.1 kHz to 30 dB at 25.6 kHz, indicating that the auditory systems of these seals are quite efficient at extracting signals from background noise. This study demonstrates that spotted seals possess sound reception capabilities different from those previously described for ice seals, and more similar to those reported for harbor seals (Phoca vitulina). The results are consistent with the amphibious lifestyle of these seals and their apparent reliance on sound. The hearing data reported herein are the first available for spotted seals and can inform best management practices for this vulnerable species in a changing Arctic.
... Spectrograms were calculated from 512-point fast Fourier transforms, with a corresponding frequency bandwidth of 39 Hz. Some calls contained wideband extraneous noise that extended into frequency ranges higher than the cutoff at 12 kHz; however, noise above this level was not considered a significant contribution to the overall sound of the Schusterman 1987; Renouf 1991). For each call we measured the following acoustic characteristics using methods described in detail in Phillips and Stirling (2000): duration (ms), number of parts per call, harmonic interval (Hz), frequency of the lowest visible harmonic at the onset, maximum, and end of the call (Hz), period (ms) and range (Hz) of rhythmic frequency modulation (FM), when present, and the frequency of the first energy peak (Hz) of the call. ...
We describe the vocal repertoire of male and female South American fur seals (Arctocephalus australis) breeding at Punta San Juan, Peru, the first such description for any member of the genus. We distinguished 11 call types, which we grouped into four functional classes: investigative, threat, submissive, and affiliative calls. Barking is used during non-agonistic investigation of other individuals. Threat calls of South American fur seals show gradation of structure, form, and apparent meaning, and are grouped into two series: nontonal or respiratory sounds, and pulsed or guttural sounds that sometimes include a terminal tonal component. This might be adaptive in enabling display behavior to be flexible in agonistic situations, allowing participants to interpret situations on the basis of contextual cues and their own physical ability and experience. In contrast, vocal displays such as submissive, full-threat, and affiliative calls tend to have a discrete acoustic structure. Of these, full-threat, female-attraction, and pup-attraction calls share acoustic characteristics: all are long, loud calls composed of both pulsed and tonal components, and show sufficient variation to allow individual recognition. We attempt to establish a base line for standardizing nomenclature and acoustic analysis, to facilitate further comparative research on the vocal repertoire of Arctocephalus species.
... None ofthe 500-, 100-or 50-ms thresholds for the harbour seal studied here were higher than the highest threshold per frequency for the above species. The lowest threshold (57 dB (re 1 ~Pa) at 8 kHz) matches (although not at the same frequency) the lowest phocid ( Ridgway and Joyce 1975) and otariid (Moore and Schusterman 1987) values reported. The various audiograms exhibit some variability (e.g., compare the two harbour seals in Fig. 1) but the differences are slight. ...
Underwater hearing thresholds of a harbour seal (Phoca vitulina) were obtained from 1 to 64 kHz using sinusoidal pulses as short as 0.5 ms. The lowest threshold was 57 dB (re 1 μPa) at 8 kHz. Thresholds for 500- to 50-ms tones increased to about 70 dB (re 1 μPa) in the 1- to 4-kHz and 32-kHz ranges and to 111 dB (re 1 μPa) at 64 kHz. At 50 ms duration, thresholds were from 0 to 6 dB greater than the maximum sensitivity for each frequency tested. Thus, only very brief seal vocalizations are not as audible as longer (and equally loud) underwater calls. For pulses shorter than 400 cycles, the thresholds increased linearly with the logarithm of the number of cycles, independent of frequency (4–32 kHz). The total energy of the pulses at threshold was estimated. From 4 to 32 kHz, as the pulse durations shortened, the threshold energy value decreased and then began to increase. These findings bring into question the concept that when presented with high-frequency sound, the auditory system integrates energy for a specific time period.
... Spectrograms were calculated from 512-point fast Fourier transforms, with a corresponding frequency bandwidth of 39 Hz. Some calls contained wideband extraneous noise that extended into frequency ranges higher than the cutoff at 12 kHz; however, noise above this level was not considered a significant contribution to the overall sound of the Schusterman 1987; Renouf 1991). For each call we measured the following acoustic characteristics using methods described in detail in Phillips and Stirling (2000): duration (ms), number of parts per call, harmonic interval (Hz), frequency of the lowest visible harmonic at the onset, maximum, and end of the call (Hz), period (ms) and range (Hz) of rhythmic frequency modulation (FM), when present, and the frequency of the first energy peak (Hz) of the call. ...
We describe the vocal repertoire of male and female South American fur seals (Arctocephalus australis) breeding at Punta San Juan, Peru, the first such description for any member of the genus. We distinguished 11 call types, which we grouped into four functional classes: investigative, threat, submissive, and affiliative calls. Barking is used during non-agonistic investigation of other individuals. Threat calls of South American fur seals show gradation of structure, form, and apparent meaning, and are grouped into two series: nontonal or respiratory sounds, and pulsed or guttural sounds that sometimes include a terminal tonal component. This might be adaptive in enabling display behavior to be flexible in agonistic situations, allowing participants to interpret situations on the basis of contextual cues and their own physical ability and experience. In contrast, vocal displays such as submissive, full-threat, and affiliative calls tend to have a discrete acoustic structure. Of these, full-threat, female-attraction, and pup-attraction calls share acoustic characteristics: all are long, loud calls composed of both pulsed and tonal components, and show sufficient variation to allow individual recognition. We attempt to establish a base line for standardizing nomenclature and acoustic analysis, to facilitate further comparative research on the vocal repertoire of Arctocephalus species.
... These results demonstrate the robust nature of psychophysical methods in measuring marine mammal hearing sensitivity, and provide strong support for a generalized California sea lion underwater hearing sensitivity curve. As data from previous psychophysical and electrophysiological studies with California sea lions, Steller sea lions (Eumetopias jubatus), and northern fur seals (Callorhinus ursinus) have suggested that the otariids form a functional hearing group (Moore and Schusterman, 1987;Babushina et al., 1991;Kastelein et al., 2005;Mulsow and Reichmuth, 2010), it is very likely that the "California sea lion underwater audiogram" can be generalized as a baseline hearing curve for extant otariid species. ...
Auditory evoked potential (AEP) data are commonly obtained in air while sea lions are under gas anesthesia; a procedure that precludes the measurement of underwater hearing sensitivity. This is a substantial limitation considering the importance of underwater hearing data in designing criteria aimed at mitigating the effects of anthropogenic noise exposure. To determine if some aspects of underwater hearing sensitivity can be predicted using rapid aerial AEP methods, this study measured underwater psychophysical thresholds for a young male California sea lion (Zalophus californianus) for which previously published aerial AEP thresholds exist. Underwater thresholds were measured in an aboveground pool at frequencies between 1 and 38 kHz. The underwater audiogram was very similar to those previously published for California sea lions, suggesting that the current and previously obtained psychophysical data are representative for this species. The psychophysical and previously measured AEP audiograms were most similar in terms of high-frequency hearing limit (HFHL), although the underwater HFHL was sharper and occurred at a higher frequency. Aerial AEP methods are useful for predicting reductions in the HFHL that are potentially independent of the testing medium, such as those due to age-related sensorineural hearing loss.
... In terms of absolute sensitivity and frequency range of hearing, this subject's aerial psychophysical audiogram is most similar to those of the northern fur seal (Callorhinus ursinus, Moore and Schusterman, 1987;Babushina et al., 1991) and the Steller sea lion (Mulsow and Reichmuth, 2010). The thresholds in the range of best hearing are lower than those previously obtained with a California sea lion in a quiet environment (Moore and Schusterman, 1987). The aerial thresholds of the California sea lion tested by Moore and Schusterman did not appear to be noise limited, and the apparent differences between that subject and the sea lion in the current study are probably due to intersubject differences in hearing capabilities. ...
Although electrophysiological methods of measuring the hearing sensitivity of pinnipeds are not yet as refined as those for dolphins and porpoises, they appear to be a promising supplement to traditional psychophysical procedures. In order to further standardize electrophysiological methods with pinnipeds, a within-subject comparison of psychophysical and auditory steady-state response (ASSR) measures of aerial hearing sensitivity was conducted with a 1.5-yr-old California sea lion. The psychophysical audiogram was similar to those previously reported for otariids, with a U-shape, and thresholds near 10 dB re 20 μPa at 8 and 16 kHz. ASSR thresholds measured using both single and multiple simultaneous amplitude-modulated tones closely reproduced the psychophysical audiogram, although the mean ASSR thresholds were elevated relative to psychophysical thresholds. Differences between psychophysical and ASSR thresholds were greatest at the low- and high-frequency ends of the audiogram. Thresholds measured using the multiple ASSR method were not different from those measured using the single ASSR method. The multiple ASSR method was more rapid than the single ASSR method, and allowed for threshold measurements at seven frequencies in less than 20 min. The multiple ASSR method may be especially advantageous for hearing sensitivity measurements with otariid subjects that are untrained for psychophysical procedures.
... Aerial hearing data for otariid pinnipeds (sea lions and fur seals) have demonstrated that these species are sensitive to aerial sound across a wide range of frequencies (Schusterman, 1974; Moore and Schusterman, 1987; Babushina et al., 1991; Kastak and Schusterman, 1998; Mulsow and Reichmuth, 2010), with absolute sensitivities similar to those of terrestrial carnivores (Fay, 1988). These findings are consistent with the importance of aerial vocalizations in otariid behaviors such as the maintenance of breeding territories (Peterson and Bartholomew, 1969; Fernandez-Juricic et al., 2001; Gwilliam et al., 2008) and the mutual recognition of mothers and pups (Trillmich, 1981; Gisiner and Schusterman, 1991; Insley et al., 2003). ...
Measurements of the electrophysiological auditory steady-state response (ASSR) have proven to be efficient for evaluating hearing sensitivity in odontocete cetaceans. In an effort to expand these methods to pinnipeds, ASSRs elicited by single and multiple simultaneous tones were used to measure aerial hearing thresholds in several California sea lions (Zalophus californianus) and Steller sea lions (Eumetopias jubatus). There were no significant differences between thresholds measured using the single and multiple ASSR methods, despite the more rapid nature of data collection using the multiple ASSR method. There was a high degree of variability in ASSR thresholds among subjects; thresholds covered a range of ∼40 dB at each tested frequency. As expected, ASSR thresholds were elevated relative to previously reported psychophysical thresholds for California and Steller sea lions. The features of high-frequency hearing limit and relative sensitivity of most ASSR audiograms were, however, similar to those of psychophysical audiograms, suggesting that ASSR methods can be used to improve understanding of hearing demographics in sea lions, especially with respect to high-frequency hearing. Thresholds for one Steller sea lion were substantially elevated relative to all other subjects, demonstrating that ASSR methods can be used to detect hearing loss in sea lions.
... However, when compared to humans (Scharf 1970) and other small terrestrial mammals (Seaton and Trachiotis 1975;Gourevitch 1965;Watson 1963), several odontocetes have slightly lower CRs (Au 1993;Au and Moore 1990;Moore and Schusterman 1987). A lower CR means that the masking band appears to widen at low and very high frequencies. ...
Thesis (M.M.A.)--University of Washington, 2001. Includes bibliographical references (leaves 60-70).
Otariids face many unique challenges with respect to lifestyle and habitat. They need to find suitable foraging areas in the open ocean, detect and capture moving prey in near darkness, identify suitable mating partners in traditional terrestrial breeding areas, and relocate their pups following extended separations. Above all, otariids have to cope with the different physical properties of air and water. This chapter illustrates how the challenges of amphibious living have shaped the sensory systems considered to be the ‘antennae’ through which otariids gather information about the surrounding world. Our current understanding of the sensory capabilities of otariids comes from studies of both structure (anatomy, neurobiology) and function (sensitivity, performance) of specific sensory modalities. This information helps us to describe what the senses are specialized for and to identify the particular biological tasks they are probably involved in. However, future studies need to explicitly link the senses, behavior, and ecology. Altogether, this knowledge will be informative to behavioral ecologists in their attempts to determine why an otariid behaves the way it does.
Sensory receptors are specialized cells for transducing information from an animal’s environment into nerve impulses that are transmitted to the central nervous system for processing and integration to detect external variables and initiate responses that enhance survival. Each type of receptor has its own sensory modality such as photoreception (vision), mechanoreception (hearing, pressure, vibration, orientation, and acceleration), chemoreception (taste and smell), thermoreception (temperature), electroreception (electric field), and magnetoreception (magnetic field), although not all receptor types are present in every species, and some are more highly developed (i.e., provide greater acuity) than others. Although marine mammals evolved from terrestrial ancestors, the propagation and reception of light and sound in air and water are so different that these sensory systems have been modified for either a fully aquatic (Cetacea and Sirenia) or amphibious (pinnipeds and sea otters) lifestyle. Specialized tactile hairs (vibrissae) in some marine mammals, tactile sensitivity in the forepaws of sea otters, and electroreception in at least one species of Cetacea provide additional sensory information under disphotic (twilight) or aphotic (no solar light) conditions, which characterize most of the marine environment and some freshwater habitats. In contrast, chemosensory (olfaction and gustation) ability shows a convergent, evolutionary reduction associated with the transition from a terrestrial to aquatic life. Finally, emerging evidence indicates a magnetic sensory ability in Cetacea and pinnipeds for orientation and navigation during individual dives and long-distance migrations.
Due to the fragility and sensitivity of the marine environment, marine construction of an enormous scale would have a huge influence on the marine ecosystem. Thus, the influence of noise pollution of alternative airport sites on spotted seals (Phoca largha) was analysed by investigating the activity levels of spotted seals in engineering areas in this paper, and scientific results were obtained. However, studies should examine the effects of long-term noise on spotted seals. In any case, an effective way to fundamentally protect the marine ecosystem is to select sites for marine construction that are far away from the sensitive areas of marine organisms and to reduce the overall size and number of marine construction sites in the world. The results of this paper can provide a reference for marine construction in other areas, such as offshore airports, offshore drilling platforms and offshore wind farms.
Devices known as jawphones have previously been used to measure interaural time and intensity discrimination in dolphins. This study introduces their use for measuringhearing sensitivity in dolphins. Auditory thresholds were measured behaviorally against natural background noise for two bottlenose dolphins (Tursiops truncatus); a 14-year-old female and a 33-year-old male. Stimuli were delivered to each ear independently by placing jawphones directly over the pan bone of the dolphin’s lower jaw, the assumed site of best reception. The shape of the female dolphin’s auditory functions, including comparison measurements made in the free field, favorably matches that of the accepted standard audiogram for the species. Thresholds previously measured for the male dolphin at 26 years of age indicated a sensitivity difference between the ears of 2–3 dB between 4–10 kHz, which was considered unremarkable at the time. Thresholds for the male dolphin reported in this study suggest a high-frequency loss compared to the standard audiogram. Both of the male’s ears have lost sensitivity to frequencies above 55 kHz and the right ear is 16–33 dB less sensitive than the left ear over the 10–40 kHz range, suggesting that males of the species may lose sensitivity as a function of age. The results of this study support the use of jawphones for the measurement of dolphin auditory sensitivity.
In his 1934 monograph A Stroll Through the Worlds of Animals and Men, Jacob von Uexküll coined the term ‘Umwelt’ (translated by Claire Schiller (1957) as ‘phenomenal or self world’) to describe the sensory, spatial, temporal and functional world unique to each species. Pinnipeds must experience a different Umwelt in the ocean than on land, since the ways in which sensory information is received, attended to and processed are likely to be dissimilar in each place. Not only are the properties of physical energy transmission altered as the animal switches environments, the frame of reference for all sensory interpretation changes time scale because the speed of the animal’s movement and of sound energy transmission is much faster in water. In the sea where they feed, their locomotion is swift in gravity-reduced space, allowing them to travel long distances and move rapidly in three dimensions to capture prey or escape the few predators they must avoid in the ocean. On land where they breed, they move with clumsy heaviness, needing only to know the location of their slow-moving pups, mates and competitors, and sense the approach of terrestrial enemies in enough time to escape into the adjacent water where pursuit ceases.
How sound spreads from water to the inner ear in seals is a problem of particular interest, because seals are semiaquatic mammals and their ears have been adapted secondarily for functioning also in water.
Research on the auditory and echolocation performance of Tursiops truncatus since 1980 has proceeded slowly due to limited resources and the expense of conducting basic psychoacoustic research as compared to more general studies concerned with the natural history of the species. Echolocation is essentially a special extension and adaptation of the marine mammal hearing system coupled with an ability to generate sounds. Humans have the ability to judge room size based on reverberation from their own voice and some blind people use self generated sounds to detect reflective objects (Rice, 1966). Echolocation can be thought of as representing a highly refined acoustic ability on a broad acoustic sensory continuum.
Experimental investigations of sound-conducting tracts in man, seals and dolphins are reviewed. Underwater hearing is considered in connection with anatomical, morphological, and functional features of species and ecological factors.
The function of the mammalian external and middle ears (at least in terrestrial mammals) appears qualitatively similar. The external ear collects sound power and couples the collected power to the middle ear, and the middle ear transmits the power to the inner ear via motion of the tympanic membrane and ossicles. However, there are large differences in the scale and form of mammalian middle and external ears (Fig. 6.1), e.g., the African elephant (Loxodonta africana) has an external ear flap or pinna with an area of about 106 (mm)2 and a tympanic membrane area of almost 103 (mm)2, whereas the dwarf shrew (Suncus etruscus) has a pinna flap of only 10 (mm)2 and a tympanic membrane area of only 1 (mm)2 (Fleischer 1973; Heffner, Heffner, and Stichman 1982). There are also differences in the orientation and relative size of the ossicles (Fig. 6.1). In Loxodonta, the linear dimensions of the malleus are about twice those of the incus and the long arm of the malleus (the manubrium) is nearly vertical (perpendicular to the horizontal plane). In Suncus, the linear dimensions of the malleus are three to four times those of the incus and the manubrium of the malleus runs nearly parallel to the horizontal plane.
Auditory evoked potential (AEP) measurements are useful for describing the variability of hearing among individuals in marine mammal populations, an important consideration in terms of basic biology and the design of noise mitigation criteria. In this study, hearing thresholds were measured for 16 male California sea lions at frequencies ranging from 0.5 to 32 kHz using the auditory steady state-response (ASSR), a frequency-specific AEP. Audiograms for most sea lions were grossly similar to previously reported psychophysical data in that hearing sensitivity increased with increasing frequency up to a steep reduction in sensitivity between 16 and 32 kHz. Average thresholds were not different from AEP thresholds previously reported for male and female California sea lions. Two sea lions from the current study exhibited abnormal audiograms: a 26-yr-old sea lion had impaired hearing with a high-frequency hearing limit (HFHL) between 8 and 16 kHz, and an 8-yr-old sea lion displayed elevated thresholds across most tested frequencies. The auditory brainstem responses (ABRs) for these two individuals and an additional 26-yr-old sea lion were aberrant compared to those of other sea lions. Hearing loss may have fitness implications for sea lions that rely on sound during foraging and reproductive activities.
Underwater audiograms are available for only a few odontocete species: Phocoena phocoena (Andersen, 1970), Inia geoffrensis (Jacobs and Hall, 1972), Tursiops truncatus (Johnson, 1967), Delphinapterus leucas (White et al., 1978), Orcinus orca (Hall and Johnson, 1971), and Pseudorca crassidens (Thomas et al., 1988). All odontocetes studied have the typical U-shaped mammalian hearing curve and hear over a wide range of frequencies (up to 120 kHz in belugas and up to 140 kHz in bottlenose dolphins). Low-frequency hearing among these species is comparable, but the high frequency cut-off is species-specific.
The hypothesis that echolocating dolphins best receive acoustic signals over the pan bones of the lower jaw is widely accepted. Studies in echolocation and hearing have assumed that those areas serve as the dolphin’s peripheral hearing system. The research that established that model, however, does not exclude other potential sound reception sites and suggests that additional areas of the head may be acoustically sensitive and perhaps frequency dependent. Using jawphones, relative hearing thresholds for representative frequencies (10, 30, 60, and 90 kHz) were behaviorally measured at over 40 sites on a dolphin’s head. Iso‐sensitivity curves were constructed and projected onto the image of a dolphin’s head based on these measurements. The results suggest sensitivity to high frequency along the lower jaw with greater sensitivity forward of the pan bone area, sensitivity to low frequency around the external auditory meatus, and an acoustic asymmetry with greater sensitivity favoring the right side of the head. These results may correlate to underlying anatomical features and suggest a more complex peripheral hearing system than has been previously assumed.
Underwater audiograms are available for a few pinnipeds from the families otariidae and phocidae, but little is known about hearing abilities in the monachid seals. A young male Hawaiian monk seal (M o n a c h u s s c h a u i n s l a n d i) was trained at Sea Life Park on Oahu, Hawaii for an underwater hearing test using a go/no‐go response paradigm. Over a 6‐month period, auditory thresholds from 2 to 48 kHz were measured using an up/down staircase psychometric technique. The resulting audiogram shows a somewhat narrower hearing range than for other pinnipeds. The monk seal’s hearing was most sensitive (20 dB above maximum sensitivity) between 12 and 28 kHz. Below 8 kHz, the Hawaiian monk seal’s hearing was less sensitive than other pinnipeds measured. High‐frequency sensitivity dropped off sharply above 30 kHz, as has been reported for other otariids, C a l l o r h i n u s and Z a l o p h u s. Phocid seals, P h o c a h i s p i d a, P. g r o e n l a n d i c a, and P. v i t u l i n a, have a broader hearing range with the upper limit near 60 kHz.
The linear-polarization character of photoluminescence (PL) from the cleaved edge surface of columnar InAs/GaAs self-assembled quantum dots (QDs) has been investigated. The columnar QDs were fabricated by closely stacking the Stranski-Krastanov-mode InAs-island layers. Anisotropy of the PL polarization depends on the stacking layer number. The single-island-layer sample shows strong transverse-electric (TE)-mode PL. With increasing stacking layer number, the PL-intensity ratio of TE-mode PL to transverse-magnetic (TM)-mode PL decreases. Then, the TE/TM-mode PL-intensity ratio is inverted beyond the stacking layer number of 9. Our results suggest that a polarization-independent transition can be accomplished by controlling the stacking layer number.
The masked pure tone thresholds of a harbour seal (Phoca vitulina) were measured at various angles using a white noise masker. The white noise source was placed at 0°, 30°, 60°, and 90° relative to the midline of the seal's head (0°). The masked pure tone thresholds for each angle were determined at 2, 4, 8, and 16 kHz. As the angle separating the signal and noise sources increased from 0° to 90°, the critical ratios of the harbour seal decreased by 1–4 dB. This shift in masked thresholds from a reference point of 0° azimuth was significant (H = 10.374, df = 3,16, p < 0.05). No significant difference was found in masked thresholds between 0° and 30° or between 60° and 90°. This indicates that if a noise source is separated by more than 30° relative to the location of a vocalizing seal, signal detection thresholds will be enhanced and communication distances increased.
In-air pure tone detection thresholds of a harbour seal (Phoca vitulina) were measured using behavioural psychophysical techniques. Thresholds dropped from about 70 dB re 20 μPa at 0.1 kHz to about 35 dB re 20 μ Pa at 4 kHz and then increased to about 45 dB re 20 μPa at 16 kHz. Increased sensitivities at 2 and 8 kHz, which have been reported in other pinnipeds, were not evident. In-air intensity detection thresholds averaged 32 dB above their underwater counterparts (1–16 kHz). Masking studies found the critical ratios at 0.25, 0.5, and 1 kHz to be 24, 15, and 21 dB, respectively (white noise masker). From 0.2 to 1.5 kHz, bandwidths 20 dB below the level of pure tone maskers were 0.16–0.18 kHz. Circumstantial evidence suggests the possibility that blood vascular changes associated with diving might also influence the sensitivity of the auditory systems of seals. Under optimal conditions, a pup's airborne cries may be detected by its mother at ranges of 1 km or more.
Background noises mask the detection of sound throughout a limited frequency range termed the critical bandwidth. Critical bandwidths of a harbour seal (Phoca vitulina) were measured, using behavioural psychophysical techniques, by indirect (critical ratios) and direct (two-tone masking) methods underwater and in air. Underwater critical ratios were determined at 4, 8, 16, and 32 kHz, using white noise spectrum levels of 50, 56, 60, and (or) 70 dB re 1 μPa. The critical ratios (pooled data, threshold ±SD) were 19 ± 9, 22 ± 7, 25 ± 7, and 27 ± 5 dB for the respective frequencies. In-air critical ratios were determined at 2, 4, 8, and 16 kHz, using white noise spectrum levels ranging from 23 to 50 dB re 20 μPa. The critical ratios (pooled data) were 25 ± 8, 23 ± 10, 21 ± 15, and 23 ± 16 dB for the respective frequencies. The arithmetic mean of the critical ratios in both media was 23 dB. This suggests that the seal is equally sensitive to pure tone signals in the presence of broad band noise in both air and water. Direct measurements of the critical bandwidth underwater were determined at 4, 8, 16, and 32 kHz, using a pure tone masker ranging from 96 to 120 dB re 1 μPa. In-air direct measurements of the critical bandwidth were measured at 2, 4, and 8 kHz, using a pure tone masker set at 80 dB re 20 μPa. The bandwidths, estimated at 23 dB below the masking level, were all under 2.25 kHz and become proportionately narrow at higher frequencies. These results show a narrow critical bandwidth for the harbour seal, thus indicating high frequency resolution in both media. The directly measured critical bandwidths from the two-tone masking study were not 2.5 times the critical bandwidth estimated from the critical ratios, as previously reported in some other mammals.
Auditory sensitivity in pinnipeds is influenced by the need to balance efficient sound detection in two vastly different physical environments. Previous comparisons between aerial and underwater hearing capabilities have considered media-dependent differences relative to auditory anatomy, acoustic communication, ecology, and amphibious life history. New data for several species, including recently published audiograms and previously unreported measurements obtained in quiet conditions, necessitate a re-evaluation of amphibious hearing in pinnipeds. Several findings related to underwater hearing are consistent with earlier assessments, including an expanded frequency range of best hearing in true seals that spans at least six octaves. The most notable new results indicate markedly better aerial sensitivity in two seals (Phoca vitulina and Mirounga angustirostris) and one sea lion (Zalophus californianus), likely attributable to improved ambient noise control in test enclosures. An updated comparative analysis alters conventional views and demonstrates that these amphibious pinnipeds have not necessarily sacrificed aerial hearing capabilities in favor of enhanced underwater sound reception. Despite possessing underwater hearing that is nearly as sensitive as fully aquatic cetaceans and sirenians, many seals and sea lions have retained acute aerial hearing capabilities rivaling those of terrestrial carnivores.
Auditory thresholds were behaviorally measured for two Atlantic bottlenose dolphins (Tursiops truncatus); a 14-year-old female, and a 33-year-old male. Stimuli were delivered directly to the lateral sides of the lower jaw via jaw phones as opposed to free-field broadcasts. The femaletextquoterights audiogram clearly reflects the standard for this species [C. S. Johnson, in Marine Bio-Acoustics, edited by W. N. Tavolga, pp. 247textendash260 (1967)]. Previous thresholds for the male measured at age 26 indicated a hearing loss in the left ear of approximately 2 to 3 dB [re: 1textmuPa] between 4 to10 kHz, which were considered unremarkable. At age 33, the same male demonstrates distinctive losses. The right ear shows a 16textendash33-dB loss over 10textendash40 kHz, the range of best sensitivity. Above 55 kHz, the right ear is 2textendash3 dB more sensitive than the left. Both ears then decline to an upper frequency cutoff of approximately 70 kHz below the standard 120 kHz. Hearing losses due to age have been reported for this species [S. H. Ridgway and D. A. Carder, J. Acoust. Soc. Am. 101, 590textendash594 (1997)]. The data reported in this paper suggest both uni- and bilateral hearing losses in the male which may be the result of age, impairment of the auditory system, or both.
Underwater vocalization and the functional structure of different vibrissae of the ringed seal (Phoca hispida saimensis) of Lake Saimaa, Eastern Finland, were studied. These seals live in darkness under the ice cover for several months during the year. It is known that blind seals are managing well in the lake. Visibility under water in some parts of the area where the seals live is only 2 m. It is suggested that echolocation is used in orientation and feeding. The Saimaa seal has click and click trial underwater vocalizations. However, both the frequency and intensity of the vocalization are low compared with, for example, those of dolphins. The structural adaptations for underwater sound localization are also not well developed.
The ringed seal has, however, extremely well-developed vibrissae. The innervation of one vibrissa is more than 10 times greater than normally found in mammals. The main structural deviations from normal mammalian vibrissae are: (1) an upper cavernous sinus, (2) a groove in the wall of the capsule at the level of the lower cavernous sinus, (3) elasticity of the connective tissue bands fixing the hair root to the capsule in the lower cavernous sinus and especially (4) the structure and innervation of the ring sinus area. Sensory elements are situated upon the glassy membrane on the surface of the outer rootsheath and in the basal cell layer of the outer rootsheath which is like a sensory epithelium. Below this epithelium a layer of liquid or gelatinous material and large amounts of glycogen are found. This sensory epithelium is especially well developed in the superciliary vibrissae. These vibrissae are protruded some millimetres when the seals are attentive. It is suggested that the vibrissae also sense sounds, which are transmitted to the sensory elements by tissue conduction through the capsule wall and via the blood sinuses. The seals may possibly detect compressional waves with the vibrissae.
The evolutionary steps leading up to the origin of cetaceans involved pervasive changes in the masticatory apparatus, the ear, and limb morphology. These changes bear heavily on the phylogenetic relationships of Cetacea, and are investigated here on the basis of two of its earliest members:Pakicetus andAmbulocetus. A phylogenetic analysis of cetaceans, five groups of mesonychians, and five other groups of ungulates indicates thatPakicetus is the sister group to all other cetaceans, and that Cete (mesonychians and Cetacea) is a monophyletic group.
Ultrasonic coded transmitters (UCTs) producing frequencies of 69-83 kHz are used increasingly to track fish and invertebrates in coastal and estuarine waters. To address concerns that they might be audible to marine mammals, acoustic properties of UCTs were measured off Mission Beach, San Diego, and at the U.S. Navy TRANSDEC facility. A regression model fitted to VEMCO UCT data yielded an estimated source level of 147 dB re 1 μPa SPL @ 1 m and spreading constant of 14.0. Based on TRANSDEC measurements, five VEMCO 69 kHz UCTs had source levels ranging from 146 to 149 dB re 1 μPa SPL @ 1 m. Five Sonotronics UCTs (69 kHz and 83 kHz) had source levels ranging from 129 to 137 dB re 1 μPa SPL @ 1 m. Transmitter directionality ranged from 3.9 to 18.2 dB. Based on propagation models and published data on marine mammal auditory psychophysics, harbor seals potentially could detect the VEMCO 69 kHz UCTs at ranges between 19 and >200 m, while odontocetes potentially could detect them at much greater ranges. California sea lions were not expected to detect any of the tested UCTs at useful ranges.
Underwater noise was recorded from three different types of wind turbines in Denmark and Sweden (Middelgrunden, Vindeby, and Bockstigen-Valar) during normal operation. Wind turbine noise was only measurable above ambient noise at frequencies below 500 Hz. Total sound pressure level was in the range 109-127 dB re 1 microPa rms, measured at distances between 14 and 20 m from the foundations. The 1/3-octave noise levels were compared with audiograms of harbor seals and harbor porpoises. Maximum 1/3-octave levels were in the range 106-126 dB re 1 microPa rms. Maximum range of audibility was estimated under two extreme assumptions on transmission loss (3 and 9 dB per doubling of distance, respectively). Audibility was low for harbor porpoises extending 20-70 m from the foundation, whereas audibility for harbor seals ranged from less than 100 m to several kilometers. Behavioral reactions of porpoises to the noise appear unlikely except if they are very close to the foundations. However, behavioral reactions from seals cannot be excluded up to distances of a few hundred meters. It is unlikely that the noise reaches dangerous levels at any distance from the turbines and the noise is considered incapable of masking acoustic communication by seals and porpoises.
Masked underwater pure tone thresholds were obtained for two female northern fur seals using an “up‐down stair case” method and a “go/no‐go” response procedure. Thresholds were determined at three continuous broadband masked noise levels at frequencies of 2, 4, 8, 16, and 32 kHz. The critical ratio (C. R.), defined as the ratio of signal power to spectrum level at masked threshold, were calculated for both animals. A psychometric function relating the pooled C. R.'s to frequency was plotted and found to be similar and showed parallel functions with C.R.'s of other marine and terrestrial mammals. These results support the contention that similar functions represent similar mechanisms that are related across species. [Work supported by ONR.]
The results of repeated determinations of the audibility curve of chinchilla confirm onr previous findings. The masked thresholds for tones were determined as functions of the level of a broad‐band noise at three frequencies: 360, 1000, and 4000 cps. For masking greater than 15 dB, these functions were linear with slope near 1. The critical ratio at masked threshold was determined at 17 frequencies over the range from 90 to 22 800 cps. The critical ratio increases with frequency and is greater than those measures for cat and man. These results are consistent with the chinchilla's range of hearing and the length of its basilar membrane. [Work supported by Public Health Service Prograin‐Project grant No. B‐3856 from the National Institute of Neurological Diseases and Blindness, National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Thresholds for pure tones masked by broad band white noise were measured in the bat,Rhinolophus ferrumequinum, using a classically conditioned response to shock. The critical ratios obtained from the masked thresholds differ from those obtained from other mammals in that some of the fine structure of the behavioural hearing curve is reflected in the critical ratio curve. This difference is discussed in relation to specializations of the auditory system of this bat.
Statistical comparison of five parameters of hearing among mammals in general and among seven animals selected to approximate phylogenetic sequence of man's ancestors; analysis indicates high- frequency and low-frequency sensitivity, lowest threshold, best frequency, and area of audible field; very high frequency was characteristic of mammals; in man this property was replaced by widest ears for sound localization properties.
Behavioral capabilities of seals and sea lions (the pinnipeds) are described and summarized in tabular form. Major features of sound detection, pitch perception, sound localization, visual spectral sensitivity, visual acuity, learning potential and constraints on learning and memory, and maximum diving depths are presented for these large-brained amphibious marine mammals. Among those species tested, phocids hear higher frequencies under water than do otariids and the opposite is true for airborne sounds. All pinnipeds are more sensitive to underwater sounds than they are to airborne sounds. There is little evidence to support the notion that most pinnipeds have evolved an echolocation capability. Scotopic sensitivity of several species is correlated with radiant energy in the marine environment. Visual acuity is equally sharp in air and under water, but deteriorates more rapidly in air than in water when the ambient light is decreased. Sea lions generally behave optimally when confronted with ambiguous cues signaling food reward. Although visual form discrimination and generalization is highly developed, thus far abstraction abilities have not been demonstrated easily in pinnipeds. Although many pinnipeds dive to 200–250 m, only the Weddell seal has been observed to dive to 600 m.
A sea lion (Z a l o p h u s c a l i f o r n i a n u s) and a porpoise (T u r s i o p s t r u n c a t u s) were trained to report the presence of a pure tone under water in yes–no psychophysical procedures. Signal probability was held constant at 0.50. For the sea lion signal strength and payoff matrix were varied concurrently while only payoff matrix was varied for the porpoise. Payoff matrix was manipulated by changing the amount of reinforcement (number of fish) consequent on the two different classes of correct responses—hits and correct rejections. In terms of the ratio of hits to correct rejections the matrix was varied over three values—1:1, 4:1, and 1:4. In the sea lion signal detection improved as signal intensity increased and was independent of the sea lion’s response bias. In the porpoise changes in response bias occurrred as a function of changes in the payoff matrix. Both the sea lion and the porpoise repeatedly demonstrated rapid acquisition of a stable response bias. These experiments demonstrate that varying the payoff matrix may be an effective way to control response bias in experiments dealing with the detection of underwater signals by marine mammals. Subject Classification: 80.50, 80.60.
Five descriptive parameters of hearing—high‐frequency and low‐frequency sensitivity, lowest threshold. best frequency, and area of the audible field—are compared statistically, first, among mammals in general, and then, among seven animals selected to approximate a phylogenetic sequence of man's ancestors. Three potentially explanatory parameters body size, maximum binaural time disparity, and recency of common ancestry with man—are also explicitly included in the analysis. The results show that: high‐frequency hearing (above 32 kHz) is a characteristic unique to mammals, and, among members of this class, one which is commonplace and primitive. Being highly correlated with functionally close‐set ears, it is probably the result of selective pressure for accurate sound localization. Low‐frequency hearing improved markedly in mankind's line of descent, but the kind and degree of improvement are not unique among mammalian lineages. High sensitivity developed in the earliest stages of man's lineage and has remained relatively unchanged since the simian level. The frequency of the lowest threshold has declined in Man's lineage—the greatest drop probably occurring during the Eocene. The total area of the audible field increased until the Eocene and has decreased since then.
On the basis of previous behavorial experiments on sound localization under water along with sound–skullmeasurements in water, it was hypothesized that the California sea lion (Z a l o p h u s c a l i f o r n i a n u s) is capable of discriminating an intensity difference of approximately 3 dB at 16 kHz. The present experiment confirmed this hypothesis by means of a series of behavorial psychophysical experiments. Subject Classification: [43]80.50, [43]80.60.
Aerial audiograms were obtained in a specially constructed acoustic chamber from three otariid pinnipeds—two yearling female Callorhinus and one 2‐yr‐old female Zalophus. A “go/no‐go” response procedure was used and threshold estimates were obtained by a tracking method. Behavioral measurements at 1, 2, 4, 8, 16, 24, and 32 kHz resulted in average thresholds for the two Callorhinus, in the order of frequencies given above, of 29, 9, 22, 13, 7, 22, and 34 dB re0.0002 dyn/cm2, and for the one Zalophus they were, respectively, 41, 19, 26, 16, 28, 37, and 61 dB re 0.0002 dyn/cm2. The thresholds for Callorhinus, although inferior in air compared to in water, show good accommodation for hearing airborne sounds. The present results from Zalophus indicate that a previous study [R. J. Schusterman, J. Acoust. Soc. Am. 56, 1248–1251 (1974)] was noise limited in threshold determinations below 24 kHz. Although only a limited number of species have been looked at, the otariid pinnipeds appear to be more sensitive to airborne sounds than do the phocid pinnipeds. [Work supported by ONR.]
In order to compare the underwater hearing of otariid and phocid pinnipeds, two feral, yearling females were tested in a “go/no‐go” response procedure. Using a tracking procedure, 20 runs was the minimum number of runs for each threshold estimate. Audiograms for both seals were similar in shape and absolute threshold values. The range of maximal sensitivity for Callorhinus is between 2 and 28 kHz. Between 28 and 42 kHz there is a hearing loss of about 120 dB/octave, setting the high‐frequency cutoff for this species at 40 kHz. These results are consistent with the idea that the major difference between the underwater bearing of the otariid and phocid pinnipeds is the high‐frequency cutoff.
Individual fitness in all species of pinnipeds depends to a great extent on the transmission and reception of acoustical information transmitted in the hydrosphere as well as in the atmosphere. Major features of sound detection,pitch perception, and sound localization are available for one, or at the most, two individuals belonging to two otariid species and to four phocids. The latter hear higher frequencies under water than to otariids, and the opposite is true for airborne sounds. Masked hearing threshold experiments using center frequencies of, 4, 8, 16, and 32 kHz resulted in critical ratios (in dB) for two northern fur seals, in the order of frequencies given above, of 20, 20, 25, and 27 [P. W. Moore and R. J. Schusterman, J. Acoust. Soc. Am. 64, 587 (1978)] and for two ringed seals they were, respectively, 30, 32, 34, and 35 [J. M. Terhune and K. Ronald, J. Acoust. Soc. Am. 58, 515–516 (1975)]. Field observations suggest that startle or flight reactions to airborne noise habituate at different rates for different species, for different populations and for different groups within a population as a function of age, sex, season, and time of day. Observations of captive northern fur seals suggest that orientation toward airborne sounds may partly be a function of their hearing sensitivity. [Work supported by ONR.]
The report is intended as a ready reference concerning the standard underwater sound transducers stocked by the Underwater Sound Reference Division. It also summarizes a few of the highlights of many years spent in investigating materials, design, and construction techniques to satisfy the requirements of widely varying underwater sound measurement problems. Twenty-nine appendices present descriptions and performance characteristics of as many individual transducer types.
Pure tones were monaurally masked by white noise at 8 different sensation levels. From these data the critical band width of a masking noise was determined; also a function relating the amount of masking to the effective level of the masking noise (i.e. sensation level of a critical band). From these two empirical relations a set of contours was constructed to represent the masked threshold for pure tones heard monaurally against a background of white noise having an ideal flat spectrum at the listener's ear. Continuous speech was also masked by white noise at the same 8 levels. The shape of the curves relating thresholds of detectability and intelligibility to noise level is similar to the masking function for pure tones. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
The audibility function of a common seal was obtained in air from 1-22.5 kc/sec and in water from 1-180 kc/sec, using an operant conditioning technique. Best sensitivity in air was at about 12 kc/sec, and best sensitivity in water was at 32 kc/sec, suggesting a water-adapted ear with some accommodation power for hearing in air. The rise in threshold above best frequency in water was 60 db/octave up to 64 kc/sec, but only 12 db/octave between 90 and 180 kc/sec, the limit of the instruments used. Results are discussed in relation to human auditory thresholds in air and in water, and for bone conduction. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Masked thresholds were obtained by conditioned response techniques for each of 4 cats at 11 frequencies over the range from 125 to 16,000 cps. Narrow and wide bands of noise were used as masking stimuli. The 1st experiment shows that the function relating masking to noise level has exactly the same from for cat as for man; the signal-to-noise ratios, however, are greater for cat than for man. The critical ratio (K) is defined as the ratio of signal power to spectrum level at the masked threshold. The function relating to K to frequency was determined for cat in the 2nd experiment; this function parallels that for man, but lies 4 to 5 db. above it at most frequencies. The masking data for the cat are shown to be consistent with measurements of frequency discrimination for this animal. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
The ability of the California sea lion (Zalophus californianus) to detect intensity differences of 16?kHz pure?tone pulses was determined in a yes?no signal detection task with trial by trial feedback, using a modified method of limits similar to the ?staircase method.? Additionally, three prethreshold experiments were performed to determine the effect of stimulus presentation strategy on discrimination ability. Results of the prethreshold experiments suggest that a ?collapse? method (i.e., symmetrically reducing the intensity of the louder tone pulse in a pair and increasing the intensity of the softer) resulted in smaller threshold estimates than either an ascending or descending staircase method. Under the collapse method, a difference threshold estimate of 3.19 dB was found for 16?kHz pure?tone pulses. These results support a previous hypothesis based of behavioral underwater sound localization experiments and sound?skullmeasurements by Moore and Au [J. Acoust. Soc. Am. 58, 721?727 (1975)]. These experiments also indicated that a sea lion which persistently biased its responses by making a low rate of false alarms in an absolute threshold task [Schusterman, J. Acoust. Soc. Am. 55, 845?848 (1974)] did not bias its responses in a difference threshold task.
The objective of this study was to measure the ability of the sea lion (Z a l o p h u s c a l i f o r n i a n u s) to localize click and pulsed pure−tone signals presented in the horizontal plane. In the first experiment the Minimum Audible Angle (MAA) was determined for a click signal consisting of one cycle of a 1.0−kHz signal presented with a repetition rate of 30 Hz. Thresholds at 63% and 75% correct responses were 6° and 9°, respectively. A second experiment examined the sea lion’s ability to localize pulsed pure tones ranging in frequency from 0.25 to 4.0 kHz at only one angular displacement. The pure tones were presented in the form of a pulse train, each pulse having a duration of 20 msec, rise−fall time of 5 msec, and a repetition rate of 30 Hz. The pulsed pure−tone localization function showed that as signal frequency was increased from 250 Hz to 1.0 kHz, the sea lion’s ability to localize the signal remained relatively constant, while above 1.0 kHz there was a sharp decrement in localization ability. Subject Classification: 65.62; 80.60.
Minimum audible field, underwater audiograms from 1 to 90 kHz were obtained for two ringed seals (Pusa hispida). The audiograms exhibited a uniform sensitivity, to within ± 7 dB, in the frequency range 1 to 45 kHz. Above 45 kHz the threshold increased at a rate of 60 dB per octave. The lowest threshold was −32 dB relative to 1 μbar (68 dB re 1 μPa) at 16 kHz. The audiograms were similar to those of other phocid seals so far studied.
A sea lion (Zalophus californianus) and a porpoise (Tursiops truncatus) were trained to report the presence of a pure tone under water in yes no psychophysical procedures. Signal probability was held constant at 0.50. For the sea lion, signal strength and payoff matrix were varied concurrently while only payoff matrix was varied for the porpoise. Payoff matrix was manipulated by changing the amount of reinforcement (number of fish) consequent on the two different classes of correct responses: hits and correct rejections. In terms of the ratio of hits to correct rejections, the matrix was varied over three values: 1:1, 4:1, and 1:4. In the sea lion, signal detection improved as signal intensity increased and was independent of the sea lion's response bias. In the porpoise, changes in response bias occurred as a function of changes in the payoff matrix. The sea lion and the porpoise repeatedly demonstrated rapid acquisition of a stable response bias. These experiments demonstrate that varying the payoff matrix may be an effective way to control response bias in experiments dealing with the detection of underwater signals by marine mammals.
The results of a study to determine the pulsed pure‐tone sound‐localization capability of a California sea lion, Z a l o p h u s c a l i f o r n i a n u s, in the horizontal plane are presented. The minimum audible angle (MAA) was determined as a function of frequency from 0.5 to 16 kHz in 1‐octave steps. The results suggested that the animal utilized time‐difference cues for the lower frequencies (0.5 to 1.0 kHz) and intensity‐difference cues for the higher frequencies (4.0 to 16.0 kHz). The MAAs for the lower frequencies were smaller than for the higher frequencies, and for the transitional frequencies (2.0 to 4.0 kHz) the animal experienced extreme difficulties in localizing the sound. To further investigate the effects of sound intensity difference in the localization process, an experiment using a sea lion skull with hydrophones attached close to each bulla was conducted. Intensity differences were measured with the skull directed at different azimuths in relatioship to a sound source. The results of the measurements using the skull considered together with the behavioral data support the contention that the sea lion used both time and intensity cues for underwater localization. Subject Classification: 65.62; 80.50.
The critical ratios of two ringed seals were estimated by determining pure‐tone thresholds (yes–no, forced choice) in the presence of various noise bands. Data obtaind from both seals were pooled. The critical ratios (using spectrum noise levels of −30 and −40 dB r e 1 μbar) were 30±5.4, 32±3.8, 34±2.8, and 35±4.5 dB at 4, 8, 16, and 32 kHz, repectively. These values are consistent with findings of other mammalian species. In the open ocean, meteorological and man‐made noises below 100 kHz may mask the underwater hearing of marine mammals. As there is less than 10‐dB variation in the noise (spectrum level) above 100 kHz, an echolocation system operating in this range would be less subject to varying amounts of masking. Subject Classification: 80.50; 65.22, 65.58.
The number of turns in the cochlear spiral and length of the basilar membrane in several mammalian species were compared with the octave range and the high-and low-frequency limits of hearing. Basilar membrane length and the number of spiral turns were not related. Among ground dwelling mammals, the number of turns in the cochlear spiral was more strongly related to octave range than was basilar membrane length. Basilar membrane length was inversely related to the high-and low-frequency limits of hearing. The best estimates of high-and low-frequency limits and octave range were derived from formulas which included both the number of turns in the cochlear spiral and the basilar membrane length as factors. The number of turns in the cochlear spiral was most highly correlated with the difference between the low-frequency limit of hearing and the lowest frequency mechanically analyzed by the traveling-wave envelope, peak-shift property of the basilar membrane [von Békésy, Experiments in Hearing (McGraw-Hill, New York, 1960)]. The coefficient of correlation for the number of spiral turns and the octave difference between the lowest audible frequency and the lowest frequency distributed as a unique point of maximum displacement along the basilar membrane was r = 0.997 (P less than .001) at 60 dB SPL. Mechanisms by which the spiral form of the cochlea may affect the motion of hair cells and the selective response of the tectorial membrane to differences among traveling-wave envelope slopes and peak locations were reviewed. It was proposed that in ground dwelling mammals, the spiral form of the cochlea extends the octave range of hearing and that through mechanisms such as these increases the sensitivity of the cochlea to frequencies below the low-frequency peak-shift limit of the basilar membrane.
Estimates of the California sea lion's (Zalophus californianus) sound‐detection thresholds in air were determined by the conditioned vocalization technique, covering a frequency range of 4–32 kHz. In air, sensitivity beyond 4 kHz gradually decreased to 24 kHz, with a rapid loss in sensitivity beyond 24 kHz. An average loss of 15 dB in the aerial audiogram of Zalophus, compared to its underwater counterpart, indicated that, like the harbor and harp seals' ears, the California sea lion's ear is water adapted. In‐air hearing sensitivity of Zalophus may be best in the frequency range most characteristic of their vocal signalling during the reproductive season.
A free-field underwater audiogram from 0.76 to 100 kHz was obtained for Pagophilus groenlandicus. Areas of increased sensitivity occurred at 2 and 22.9 kHz. The lowest threshold was −32.9 db/μbar at 15.0 kHz. Above 64 kHz the threshold increases at a rate of 40 db/octave. The audiogram was similar to that of the Phoca vitulina. The effects of ambient noise on the audiogram are discussed.
Conditioning techniques were developed demonstrating that pure tone frequencies under water can exert nearly perfect control over the underwater click vocalizations of the California sea lion (Zalophus californianus). Conditioned vocalizations proved to be a reliable way of obtaining underwater sound detection thresholds in Zalophus at 13 different frequencies, covering a frequency range of 250 to 64,000 Hz. The audiogram generated by these threshold measurements suggests that under water, the range of maximal sensitivity for Zalophus lies between one and 28 kHz with best sensitivity at 16 kHz. Between 28 and 36 kHz there is a loss in sensitivity of 60 dB/octave. However, with relatively intense acoustic signals (> 38 dB re 1 mub underwater), Zalophus will respond to frequencies at least as high as 192 kHz. These results are compared with the underwater hearing of other marine mammals.
A free-field air audiogram from 1 to 32 kHz was obtained for a Pagophilus groenlandicus trained to respond to pure tone signals. The lowest threshold was at 4 kHz at a level of 29 db//0.0002 dynes/cm2. The air audiogram was generally flat. The critical ratios at 2 and 4 kHz were 10%. The lumen of the external auditory meatus is probably acoustically blocked. The outer and (or) middle ear structures and their acoustic impedance mismatch with the air are believed responsible for the comparatively irregular and slightly insensitive hearing of the seal in air.
Masked thresholds were obtained for a bottlenosed porpoise at 15 frequencies between 5 and 100 kHz, using continuous broad‐band noise to mask tonal stimuli. Critical bandwidths were calculated from the ratio of the tonal threshold level to the masking noise level per hertz at each frequency. At 5, 10, 20, 50, and 100 kHz, six different noise levels were used; from the resulting data, a plot of the amount of masking versus the effective noise level was obtained. The data are compared to those from similar experiments with human subjects.
Masked thresholds were measured with an operant tracking method at 4 frequencies between 1000 and 8000 cps and at 3–5 levels of wide‐band noise. As in humans and cats, masked thresholds in the rat increased linearly with noise level. Critical ratios were calculated from the masked thresholds and found to be 10 or 11 dB greater than those in man and 5 to 6 dB greater than those in cats. Greenwood's function Δf cb = 10 ax+b , relating critical bandwidths to position on the basilar membrane, was shown to fit reasonably well the data of this experiment. The constant relation shown by Fletcher between critical ratios and frequency DL's, previously found to apply to man and to cats, appears to apply to rats also.
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