Variation in the hearing sensitivity of a dolphin population determined through the use of evoked potential audiometry
Age and sex distribution of bottlenose dolphin subjects for which AEP audiograms were collected.
(a) Mean base line audiogram . Symbols represent mean thresholds. Error bars indicate standard deviation. The other panels are representative audiograms for dolphins with upper cutoff frequencies between (b) 100 and 140, (c) 50 and 100, and (d) below . The values presented in the legend correspond to the sex of the animal (M or F), the age of the animal, and the ID number of the animal in Table I (the last value in parentheses).
Mean audiograms for bottlenose dolphins grouped by age. Mean threshold for a given frequency was not plotted if there were fewer than four thresholds obtained at that frequency. Except for the age group, plots are terminated at ; there were a number of individuals for which data above was not obtained because (see Table II). The plot for the age group is extended so that the reduction in high frequency hearing for animals with a full range of hearing can be viewed for comparison.
Upper frequency limit of hearing , defined as the frequency at which the threshold equaled re , as a function of animal age and sex.
Audiograms of a male dolphin (No. 7 in Table I) and his male offspring (No. 30 in Table I) showing unusual patterns of hearing loss. Threshold values are means of the left and right ears standard deviation (denoted by the error bars).
Thresholds for two dolphins [a female (No. 26 in Table I) and male (No. 18 in Table I)] having significant high-frequency hearing loss. Filled symbols represent measured thresholds; open symbols indicate maximum SPLs for which no response was detected (the actual threshold would be higher). Note that thresholds are high for all frequencies at which EFRs were detected.
Subject ID number, age at time of testing, sex and upper cutoff frequency of hearing for each individual in the hearing survey. Unless otherwise noted, frequency-specific thresholds are presented for each individual and each ear. Thresholds are given as dB re: .
Mean threshold, standard deviation, and number of samples (thresholds for individual ears) for bottlenose dolphins grouped by age categories.
Results of the ANCOVA performed on utilizing sex as a fixed factor and age as a covariate.
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