Preliminary evidence for signature vocalizations among free-ranging narwhals (Monodon monoceros)a)
Narwhal shown with Crittercam (contained within the dashed ellipse) and DTAG (contained within the dashed rectangle) attached immediately before release. Photograph courtesy of Rune Dietz.
Sample spectrograms (larger, top plots) and waveforms (smaller, bottom plots) of a combined tonal/pulsed signal produced by individual (a) mm224 and (b) mm226 with a FFT size and frame length of 512 points, 50% window overlap, and a maximum frequency displayed of . The low frequency energy associated with most of the pulses is likely due to the resonance of the air sacs involved in sound production or transmission. The solid arrows in both spectrograms indicate the synchronous FM tonal component produced by the tagged animal.
Spectrogram composite of all four whistles of mm224 (a–d) and 14 of the 17 whistles of mm226 (f–s) with a FFT size and frame length of 512 points, 50% window overlap, and a maximum frequency displayed of . The remaining 3 whistles of mm226 resembled those displayed here but were excluded for graphical convenience. The waveforms displayed in subplots e and t are of the same whistles used to generate subplots d and s, respectively.
Digitized traces of the fundamental frequency contours of the whistles displayed in Fig. 3 . Each trace is shown with 100 equally spaced points that have been normalized on a horizontal time axis from 0 to 1. Again, panels a–d correspond to the whistles produced by mm224 and f–s to those by mm226. Note the difference in the frequency ranges for the two individuals.
Illustration of temporal and spectral features extracted from a traced whistle produced by mm224 (subplot d in Figs. 3 and 4 ). The initial and ending frequencies are indicated by filled circles (●) while the other spectral components are marked with horizontal dashed lines. Note that the mean frequency is closer to the minimum frequency because of the whistle’s frequency content lies below .
Illustration of points used for cross-correlation comparison of whistles (see text for the equation). In (a), contour (darker, from mm226: subplot i in Figs. 3 and 4 ) and (lighter, from mm224: subplot d in Figs. 3 and 4 ) are depicted normalized in time with their original frequency content. In (b), contour has been shifted along the frequency axis to minimize the frequency difference between the two contours. All 100 points along the contours were used to compute Eq. (1) .
Approximate depths where combined tonal/pulsed signals (triangles, ▵) and whistles (circles, 엯) were produced adjacent to a frequency histogram of depth bins (bars) for mm224 (a) and mm226 (b). The frequency plotted on the abscissa is expressed as a fraction of the total amount of time spent at all depths. The maximum depths achieved for mm224 and mm226 during the DTAG deployments were roughly 125 and , respectively.
Visual representations of temporal features of combined tonal/pulsed signals. Normalized pulse number (top two panels) and pulse repetition rate (pulses per second, bottom two panels) as a function of normalized duration. Note the clear differences in general morphology of these plots between the two individuals.
Summary statistics of the acoustic features of combined tonal/pulsed signals.
Summary statistics of the acoustic features of whistles.
Cross-correlation comparison of whistles between the same and different individuals. These data were computed in arbitrary units with higher values indicating a greater difference between the contours being compared. The intraindividual comparisons are italicized.
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