Setup for recordings of Tursiops aduncus. The recording setup was similar for the T. truncatus recordings reported in the text. t 1, t 2, and t 3 are the time-of-arrival differences between the same click arriving on the four different hydrophones. [Jensen et al. (2009b), reprinted with permission from J. Exp. Biol.]
Echolocation click signal waveform from T. aduncus and T. truncatus.
Individual power spectra (gray lines) and averaged power spectrum (black line) of all on-axis echolocation clicks from bottlenose dolphins. (a) Tursiops truncatus, recorded off Los Gigantes, Tenerife, Spain. Sampling rate 500 kHz, fast Fourier transform (FFT) size 128 points, Hann window, spectrum interpolated 10 times. (b) Indian Ocean bottlenose dolphins, Tursiops aduncus. Sampling rate 800 kHz, FFT size 128 points, Hann window, spectrum interpolated 10 times. (c) Notched box plot indicating the distribution of centroid frequency estimates for the two species overlaid on top of individual estimates. Box plot shows 25th, 50th (median), and 75th percentile of data. Whiskers indicate the most extreme data point within 1.5 interquartile range of the median.
Spectra of echolocation clicks recorded from bottlenose dolphins, Tursiops aduncus, shown for various degrees of off-axis recordings for two clicks recorded on the four-channel array. Sampling rate 800 kHz, FFT size 128 points, Hann window, spectrum interpolated 10 times. The off-axis angle in the vertical plane, calculated from a Lagrange interpolation of each click measurement (see the text for details), is indicated for each spectrum.
The centroid frequency of on-axis clicks as a function of the apparent source level (see the text for details) of clicks from Tursiops aduncus (recorded in Australia) and T. truncatus (recorded off Los Gigantes, Tenerife, Spain). The linear regression line of the T. aduncus data has the equation f 0 = 1.26·ASL − 166 with a fit of R 2 = 0.6. It is significantly different from a line with slope zero (ANOVA, p < 0.05). The linear regression line of the T. truncatus data is not significantly different from a line of slope zero and therefore not shown. The linear regression line of data from a false killer whale (Pseudorca crassidens) from Au et al. (1995) is given as comparison (f 0 = 2.55·ASL − 456 with R 2 = 0.8).
Composite directionality plot of signals from (a) Tursiops aduncus (recorded in Australia) and (b) T. truncatus (recorded off Tenerife). The off-axis angle for each click has been adjusted by finding the maximum of a Lagrange interpolated quadratic curve through the measurements (see the text for detail). Solid line is a piston model using an on-axis click from a free-ranging bottlenose dolphin, assuming a piston radius of 12.7 cm for T. aduncus and 8.4 cm for T. truncatus (for details, see Au, 1993).
Source parameters of bottlenose dolphin (Tursiops aduncus and T. truncatus) echolocation signals recorded at different field locations compared to studies made with animals in captivity.
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