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Example spectrograms of ultrasonic whistles from Icelandic killer whales (Orcinus orca): (a) below 48 kHz; (b) below 48 kHz with overlapping airflow sound; (c) above 48 kHz. Note the presence of an airflow sound entirely overlapping the whistles in (b) but not in (a). In real time only the airflow is audible, but once slowed down both the ultrasonic whistles and the airflow sound are audible (see multimedia files Mm. 1.wav and Mm. 2.wav). Recordings (a) and (c) were sampled at 192 kHz, and (b) at 96 kHz. Spectrogram parameters: FFT size: (a) 4094, (b) 2048, (c) 1024; overlap: 50%; window function: Hann; frequency resolution: [(a) and (b)] 46.875 Hz, (c) 187.5 Hz; time resolution: [(a) and (b)] 10.67 ms, (c) 2.67 ms.
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Recording made using an animal-attached sound recording tag (Dtag) sampling at 192 kHz and deployed close to the blowhole. This sound clip corresponds to the spectrogram presented in Fig. 1(b). An airflow sound is audible twice in this real time recording but not the coinciding ultrasonicwhistles. Faint clicks and a call can also be heard in the background. [URL: http://dx.doi.org/10.1121/1.3462235.1]
The same recording as in Mm. 1 but slowed down six times. The airflow sounds become clearer and the ultrasonicwhistles audible. Note that the airflow sound coincides with the whistles, suggesting it is an artifact of whistle production. [URL: http://dx.doi.org/10.1121/1.3462235.2]
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This study reports that killer whales, the largest dolphin, produce whistles with the highest fundamental frequencies ever reported in a delphinid. Using wide-band acoustic sampling from both animal-attached (Dtag) and remotely deployed hydrophone arrays, ultrasonicwhistles were detected in three Northeast Atlantic populations but not in two Northeast Pacific populations. These results are inconsistent with analyses suggesting a correlation of maximum frequency of whistles with body size in delphinids, indicate substantial intraspecific variation in whistle production in killer whales, and highlight the importance of appropriate acoustic sampling techniques when conducting comparative analyses of sound repertoires.
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