Do Dolphins’ Whistles Reveal their Age and Sex?

Abstract

Bottlenose dolphins (Tursiops truncatus) have a complex acoustic communication system composed of a variety of sounds, including narrow-band, frequency-modulated whistles. Many past studies of dolphin whistles have focused on clarifying how dolphins use a subset of whistles for self-identification, with less attention given to other qualities that whistles may reveal about a vocalizer. Acoustic features of vocalizations provide indicators of the physical characteristics of the caller (e.g., size) for many vertebrate species. To test for similar cues in dolphin whistles, we investigated whether whistles varied systematically according to the sex and age of the vocalizer. Neural networks were created to sort whistles produced by males or females, calves or adults, or from dolphins in four different age groups. Fourteen acoustic parameters of whistles were used as inputs to the networks. Results showed that neural networks were able to learn to classify whistles based on dolphin age or sex; however, networks showed relatively little ability to classify whistles other than those that they were trained to sort. No single class of acoustic cues consistently enabled networks to differentiate either males from females or older dolphins from younger dolphins. Instead, the neural networks used multiple acoustic dimensions to sort whistles. These results suggest that acoustic cues indicative of age and sex are likely present within all whistles produced by dolphins, but that these cues do not correspond to the kinds of global shifts in spectral features that would be expected from systematic age- or sex-related differences in the shape or size of sound producing membranes or acoustic resonators across individuals.

Keywords

• Vocal production
• Voice recognition
• Dolphin
• Individual recognition
• Sound production
• Whistles
• Bioacoustics
• Communication