ECHOLOCATION SIGNALS AND TRANSMISSION BEAM PATTERN OF A FALSE KILLER WHALE (PSEUDORCA CRASSIDENS)

The echolocation transmission beam pattern of a false killer whale (Pseudorca crassidens) was measured in the vertical and horizontal planes. A vertical array of seven broadband miniature hydrophones was used to measure the beam pattern in the vertical plane and a horizontal array of the same hydrophones was used in the horizontal plane. The measurements were performed in the open waters of Kaneohe Bay, Oahu, Hawaii, while the whale performed a target discrimination task. Four types of signals, characterized by their frequency spectra, were measured. Type-1 signals had a single low-frequency peak at 40±9 kHz and a low-amplitude shoulder at high frequencies. Type-2 signals had a bimodal frequency characteristic with a primary peak at 46 ±7 kHz and a secondary peak at 88±13 kHz. Type-3 signals were also bimodal but with a primary peak at 100±7 kHz and a secondary peak at 49 ±9 kHz. Type-4 signals had a single high-frequency peak at 104±7 kHz. The center frequency of the signals were found to be linearly correlated to the peak-to-peak source level, increasing with increasing source level. The major axis of the vertical beam was directed slightly downward between 0 and -5°, in contrast to the +5 to 10° for Tursiops and Delphinapterus. The beam in the horizontal plane was directed forward between 0° and -5°. In both planes, the type-1 signals had the broadest beam pattern, followed by the type-2 and type-3 signals, with the narrowest beam pattern being exhibited by the type-4 signals. The beam pattern in the horizontal plane was much narrower than the beam pattern in the vertical plane. © 1995, Acoustical Society of America. All rights reserved.