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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.

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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.

An echolocating dolphin was trained to discriminate between the material composition of two cylinders oriented at different aspect angles. The two targets for the first task were a hollow aluminum and a hollow stainless steel cylinder of the same dimension. For the second task, the targets were the hollow aluminum cylinder and a cylinder of coral rock aggregates encased in degassed epoxy. The dolphin could discriminate the aluminum and steel cylinders perfectly at aspect angles of 0 ø and 10 ø (at 0 ø, the longitudinal axis of a cylinder was perpendicular to the dolphin). The dolphin had its lowest performance (79% and 81% correct) when the cylinders were at aspect angles of 45 ø and 90 ø , respectively. The echoes from the aluminum and steel cylinders were the most similar at 45 ø and 90 ø the two angles at which the dolphin's performance was the lowest. The dolphin performed the second discrimination task between the hollow aluminum and coral rock cylinders almost perfectly, at all aspect angles considered. Differences in the occurrence time and amplitude of highlights along with the duration of the echoes seem to be important cues for discrimination of the cylinders. For a simple discrimination task such as the aluminum and coral rock targets, aspect independent information is available for discrimination at arbitrary aspect angles.