The echolocation signals of the same beluga whale (Delphinapterus leucas) were measured first in San Diego Bay, and later in Kaneohe Bay, Oahu, Hawaii. The ambient noise level in Kaneohe Bay is typically 12-17 dB greater than in San Diego Bay. The whale demonstrated the adaptiveness of its biosonar by shifting to higher frequencies and intensities after it was moved to Kaneohe. In San Diego, the animal emitted echolocation signals with peak frequencies between 40 and 60 kHz, and bandwidths between 15 and 25 kHz. In Kaneohe, the whale shifted its signals approximately an octave higher in frequencies with peak frequencies between 100 and 120 kHz, and bandwidths between 20 and 40 kHz. Signal intensities measured in Kaneohe were up to 18 dB higher than in San Diego. The data collected represent the first quantitative evidence of the adaptive capability of a cetacean biosonar system.

The echlocation signals of two Atlantic bottlenose dolphins, Tursiops truncatus, were measured while the animals were involved in a target-detection experiment conducted in open waters. The time intervals between successive pulses in a pulse train were found to be highly variable, although the intervals were longer than the time needed for an acoustic signal to travel from the animals to the target and back. Sound pressure levels of the echoranging signals were measured for target ranges of 60, 70, 75, and 80 yds. The peak-to-peak click-source level at 1 yd showed little variation with the target range; the average level was 120.4 dB re 1 μbar for one animal and 122.3 dB for the other. These open-water sound pressure levels are at least 30 dB higher than any click-source levels reported in the literature. Oscilloscope photographs and their Fourier transforms of these high-amplitude clicks are presented. The typical clicks had average durations of 40 μsec, with peak energies between 120 and 130 kHz, much higher than the previously reported energy peaks centered at 35 to 60 kHz.

In an echolocation experiment, the target detection performance of a beluga and a bottlenose dolphin were similar, but each produced different patterns of echolocation click trains. The beluga emitted three different patterns of echolocation clicks. A pattern I click train started with low-amplitude clicks, followed by packets of clicks. A packet contained several clicks with interclick intervals less than the two-way travel time to the target; the interpacket intervals were greater than the two-way travel time. A pattern II click train consisted of a combination of individual clicks, some with intervals less than and some greater than the two-way travel time. This pattern did not contain packets. The third pattern of click trains consisted of individual clicks with interclick intervals less than the two-way travel time. However, the bottlenose dolphin always emitted clicks with interclick intervals greater than the two-way travel time. These differences in click patterns suggest that the beluga has a different echolocation strategy than the bottlenose dolphin.

The propagation characteristics of high-frequency echolocation signals (peak energies above 100 kHz) of the beluga (Delphinapterus leucas) were measured while the animal performed a target detection task. The whale was trained to station on a bite plate so that its transmission beam could be measured in the vertical and horizontal planes using hydrophone arrays. The transitional region between the acoustic near- and farfields was also located using an array of hydrophones that extended directly in front of the animal in the horizontal plane. Three distinct modes of signals were observed. Mode 1 signals had click intervals greater than the time required for the signals to travel to the target and back (two-way transit time). Mode 2 signals had click intervals shorter than the two-way transit time, and mode 3 signals had high repetition rates with an average click interval of 1.7 ms, approximately 2% of the two-way transit time. The average click intervals for the modes 1 and 2 signals were 193 and 44 ms, respectively. The vertical and horizontal beam patterns of the mode 1 signals had similar 3-dB beamwidths of approximately 6.5 degrees. The major axis of the vertical beam was directed approximately 5 degrees above the plane defined by the animal's teeth. The near- to farfield transition region was approximately 0.64-0.75 m from the tip of the animal's mouth.

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