Animal sounds

Dolphins emit distinct vocalizations in the contexts of stressful situations, such as when captured in nets. It has been assumed among animal rights groups that the presence of human swimmers causes stress in captive Atlantic bottlenose dolphins (Tursiops truncatus). Stress may be expressed in dolphin vocalizations and the associated visual behaviors before, during, and after swim sessions with humans. Thus, these behaviors were recorded to elucidate quantitative vocal patterns suggestive of conspecific stress. Significant differences among vocalization types within sample sessions were found only for whistles between During II and After sessions. Other comparisons indicated no significant differences for vocalization production frequencies between the presence or absence of human swimmers. Additionally, correlations found among the seven vocalization types and all five sample sessions indicated only that one variable, i.e. the presence or absence of human swimmers, was being measured in several different ways (by the different vocalization type production frequencies). Thus, conspecific stress, if indeed it can be measured by vocalization production frequency, does not appear to occur more often in the presence of human swimmers.

The signature whistles of related Atlantic spotted dolphins ( Stenella frontalis) in the Bahamas were evaluated for similarity. Judges compared the contour patterns of signature whistles pair-wise between 19 dolphins. Whistle parameters between the signature whistles of individuals were statistically compared. There were no significant differences between the signature whistles of male and female calves when the similarity of their whistles was compared to their mothers. However, there was a tendency with female calves more likely to produce signature whistles similar to their mothers' whistles. Three out of five female calves produced signature whistles that were "very similar" or "similar" to the signature whistles of their mothers. Two out of four male calves produced signature whistles that were "similar" to the signature whistles of their mothers. The signature whistles of mother and calf pairs were more likely to be "similar" to each other than the signature whistles of sibling pairs.

Previous qualitative assessment indicated that signature whistles of temporarily captured, free-ranging dolphins remain stable over periods of 2--12 years. This study reports on the stability of signature whistle parameters in wild female Atlantic spotted dolphins in the Bahamas over five or more years and between changes in age class. Signature whistles from seven female dolphins were pooled into blocks of 'early' and 'late' years for the time assessment. Signature whistles from five females were pooled by age class for the second analysis. Duration, minimum frequency, maximum frequency, and change in frequency were measured from spectrograms of whistles for statistical analysis. No significant changes were found in any of the signature whistle parameters either between early and late periods of time or with a change in age class.