Behavioral and auditory evoked potential (AEP) audiograms of a false killer whale were measured using the same subject and experimental conditions. The objective was to compare and assess the correspondence of auditory thresholds collected by behavioral and electrophysiological techniques. Behavioral audiograms used 3-s pure-tone stimuli from 4 to 45 kHz, and were conducted with a go/no-go modified staircase procedure. AEP audiograms used 20-ms sinusoidally amplitude-modulated tone bursts from 4 to 45 kHz, and the electrophysiological responses were received through gold disc electrodes in rubber suction cups. The behavioral data were reliable and repeatable, with the region of best sensitivity between 16 and 24 kHz and peak sensitivity at 20 kHz. The AEP audiograms produced thresholds that were also consistent over time, with range of best sensitivity from 16 to 22.5 kHz and peak sensitivity at 22.5 kHz. Behavioral thresholds were always lower than AEP thresholds. However, AEP audiograms were completed in a shorter amount of time with minimum participation from the animal. These data indicated that behavioral and AEP techniques can be used successfully and interchangeably to measure cetacean hearing sensitivity.

Auditory evoked potential (AEP) procedures have been increasingly used to measure hearing processes in aquatic mammals. They have been demonstrated to be useful in measuring the audiograms of stranded animals like infant sperm whales (Physeter macrocephalus) and Risso's dolphins (Grampus griseus). Modulation rate transfer functions (MRTF) demonstrating appropriate stimulus presentation rates are usually measured prior to recording audiograms with odontocetes. Measures comparing behavioral and AEP audiograms with the same animals have generally shown good correspondence between data gathered using the two procedures. AEPs and acoustic brainstem responses (ABRs) also have been used to measure hearing while an animal is actively echolocating. This technique of measuring the animal's ability to hear its own outgoing signals, as well as the returning echoes, allows experimenters to develop a new understanding of the processes underlying echolocation.

SUMMARY An infant Risso's dolphin (Grampus griseus) was rescued from the beach in Southern Portugal, and an audiogram was measured using auditory evoked potentials (AEP) and envelope following response (EFR) techniques for frequencies from 4 to 150 kHz. The stimuli used were custom sinusoidally amplitude-modulated (SAM) tone-bursts, and the AEP responses were collected,averaged and analyzed to quantify the animal's physiological response and,thereby, hearing thresholds. The infant animal showed a wide range of best sensitivity, with the lowest threshold of 49.5 dB re. 1 μPa at 90 kHz. The audiogram showed a typical mammalian ∪-shape with a gradual, low-frequency slope of 16.4 dB octave-1 and a sharp high-frequency increase of 95 dB octave-1. When compared with an audiogram of an older Risso's dolphin obtained using behavioral methods, the threshold values at upper frequencies were much lower for this infant animal, and this infant heard higher frequencies. These results redefine the hearing capabilities of Risso's dolphins by demonstrating very high-frequency sensitivity.

prompted a great deal of work on the hearing of aquatic and semi-aquatic mammalian species (Au et al., 2000;Wartzok and Ketten, 1999;Richardson et al., 1995;Tyack et al., 2006;Nachtigall et al., 2005). The polar bear Ursus maritimus is the only bear species classified as a marine mammal (Rice, 1998), but there has been no audiometric examination of their hearing. According to the most comprehensive review of animal hearing studies (Fay, 1988), and a search of the literature published since, in fact no measurements have been completed on the hearing of any bear.One way to estimate the hearing of a species is to examine the calls of its prey and its response to those calls. Ringed seals Phoca hispida and bearded seals Erignathus barbatus are prominent in the diet of polar bears (Stirling, 2002). In some areas, the predator-prey relationship between ringed seals and polar bears is so interrelated that a count of the population of one of them can indicate the population level of the other (Stirling and Øritsland, 1995). Polar bears' preferred prey items are the newborn pups and subadults (Stirling and McEwan, 1975), and they primarily hunt seals in areas of moving pack ice, which include known important locations of seal birth lairs (Smith, 1980). Four types of vocalizations made by ringed seals can be heard at all times of day in the Arctic spring: (1) low-pitched barks, (2) high pitched yelps, (3) low and high pitched growls and (4) short descending chirps (Stirling, 1973). Sonograms of the recorded sounds indicated that most of the energy was relatively low frequency below 2·kHz, with some harmonics up to 8·kHz.The behavioral responses of polar bears to the calls of ringed seals recorded under water and then presented to the bears in air were measured (Cushing et al., 1988), and elicited similar responses from two recently captured bears. The bears erected their ears, lifted their heads, visually scanned the room and then began sniffing. As the ringed seal calls continued to be played the bears became active, paced their cage, groaned and chuffed, then pawed and chewed at their cage bars. All of these behaviors were observed only rarely in the baseline behavioral examinations prior to the presentation of ringed seal sounds, indicating that the bears responded to their primary prey's underwater vocalizations, presented in air, in a manner that indicated some importance of in-air hearing in detecting and locating their under-ice prey. Cushing's observations suggest that if polar bears could hear the underwater vocalizations of the ringed seals they might use seal vocalizations as a method to locate their favorite prey. It has also been noted (Stirling and Thomas, 2003) that the distinct trills of bearded seals might also provide a prominent cue for polar bear localization of these animals. A While there has been recent concern about the effects of sound on marine mammals, including polar bears, there are no data available measuring the hearing of any bear. The in-air hearing of three polar bears was measured using ...