Slide 24 of 37
Notes:
Bottlenose dolphins can identify through echolocation many characteristics of submerged objects, including size, structure, shape, and material composition (Au, 1993; Bel’kovich & Dubrovskiy, 1976; Nachtigall, 1980). For example, they can discriminate between circles, squares, and triangular targets covered with neoprene (Barta, 1969). They can also discriminate a 16.1-cm from a 15.2-cm diameter disk at a distance of 0.7 m (Barta, 1969). Dolphins have also been found to discriminate aluminum cylinders differing in wall thickness by as little as 0.23 mm, presented at a distance of 8 m (Au & Pawloski, 1992), as well as freely rotating three dimensional geometric objects, such as cubes, rectangular prisms and pyramids (Helweg, Roitblat, Nachtigall, & Hautus, 1996). Dolphins can also discriminate between aluminum, copper, and brass circular targets (Evans & Powell, 1967). In a number of experiments, dolphins were also found to be able to discriminate hollow aluminum cylinders (e.g., 3.81 cm OD) from the same size hollow cylinder made of stainless steel or a solid cylinder formed of coral rock pebbles embedded in degassed epoxy resin (e.g., Hammer & Au, 1980).
Echolocation clicks have peak energy at frequencies from 40 to 130 kHz with recorded source levels over 220 dB re: 1 ?Pa at 1 m. The signal is very brief, lasting about 50 ?sec. The echo returning from a cylindrical object located about 5 m in front of the animal is shown. The temporal structure of this echo corresponds to the structure and composition of the object. The corresponding spectrum of this echo is also shown.
