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Abstract: Bottlenose dolphins (Tursiops truncatus) have been observed to produce whistles coincident with bubblestream emissions from the blowhole. Use of bubblestreams concurrent with whistles by calves could function for vocalizer recognition prior to the development of a calf’s signature whistle. We observed bottlenose dolphin calves regularly producing bubblestreams with whistles and whistle-squawks during their first month of life. While vocalizations with bubblestreams may differ from whistles without a bubblestream, the former’s prominence during the observed calves’ first 30 days suggests a potentially important facet of calf acoustic development. This study focused on whistles and whistle-squawks that occurred concurrently with bubblestreams by four bottlenose dolphin calves during their first 30 days of life with the goal of better understanding the early emergence of whistle-type vocalizations. Simultaneous video and acoustic data facilitated assessment of whistle-type vocalizations (i.e., whistles and whistle-squawks) that coincided with a bubblestream emission from a focal calf. The calves’ whistle rates (per hour) were highest in Days 21 to 30 compared to Days 0 to 10 and 11 to 20. None of the focal calves developed their stereotyped signature whistle contour (as confirmed after 2 years of age), yet results showed some evidence of repetitive contour emissions during the first 30 days of life. Whistle-squawks were produced significantly more frequently than whistles as the calf aged. Whistle duration and the frequency range significantly increased over time. These data suggest that whistle production begins as early as the first days of life and that the prominence of the chaotic characteristic typical of calf tonal vocalizations persists throughout their first month. Further, whistle-type vocalizations are better able to span longer durations and reach both higher and lower frequencies as a calf develops.
Key Words: Atlantic bottlenose dolphin, Tursiops truncatus, bubblestream, whistle-type vocalizations, whistles, whistle-squawks
Page Numbers: 337-348