Beamwidth control and angular target detection in an echolocating bottlenose dolphin ( Tursiops truncatus )

• Published in: The Journal of the Acoustical Society of America Vol. 124; no. 5; pp. 3324 - 3332
• Main Authors: Moore, Patrick W., Dankiewicz, Lois A., Houser, Dorian S.
• Format: Journal Article
• Language: English
• Published: Woodbury, NY Acoustical Society of America 01-11-2008; American Institute of Physics
• Subjects: Acoustics; Animals; Auditory Threshold - physiology; Behavior, Animal; Bottle-Nosed Dolphin - physiology; Echolocation - physiology; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Hearing - physiology; Marine; Mechanoreceptors - physiology; Orientation; Physics; Posture; Sound Localization; Tursiops truncatus; Underwater sound; Vocalization, Animal; Marine animal; Vertebrata; Mammalia; Cetacea; Underwater acoustics; Target detection; Echolocation; Tursiops truncatus
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.2980453

Bottlenose dolphin (
Tursiops truncatus
) echolocation beams are typically characterized as symmetrical
−
3

dB
beamwidths; however, the functional width of the beam during target detection has not been explored. Angular target detection thresholds of an echolocating dolphin were examined to more fully describe the functional characteristics of the echolocation beam. The dolphin performed an echolocation detection task with its head held in a fixed orientation. Targets were placed 9 m in front of the dolphin [
0
°
position
(
P
0
)
] and systematically moved right or left until target detection reached chance probability. A 24-element hydrophone array placed 1 m in front of the dolphin was used to measure vertical and horizontal echolocation beamwidths. Detection thresholds were
26
°
left and
21
°
right of
P
0
for a sphere target and
19
°
left and
13
°
right of
P
0
for a cylinder target. Estimates of maximum horizontal and vertical beamwidths ranged up to
40
°
and
29
°
, respectively, and exhibited large variability. The dolphin nominally steered the maximum response axis of the echolocation beam up to
18
°
in the horizontal,
12
°
in the upward vertical, and
4
°
in the downward vertical. These results suggest that the dolphin can steer and modify the width of the echolocation beam.