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First published online June 12, 2009
Journal of Experimental Biology 212, 2105-2112 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.029033

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Four-choice sound localization abilities of two Florida manatees, Trichechus manatus latirostris

Debborah E. Colbert^1,2,4,*, Joseph C. Gaspard, 3rd^2,3, Roger Reep³, David A. Mann^2,4 and Gordon B. Bauer^2,5

¹ Association of Zoos and Aquariums, Silver Spring, MD 20910, USA
² Sensory Biology and Behavior Program, Mote Marine Laboratory and Aquarium, Sarasota, FL 34236, USA
³ College of Veterinary Medicine, University of Florida, Gainesville, FL 32610, USA
⁴ College of Marine Science, University of South Florida, St Petersburg, FL 33701, USA
⁵ Division of Social Sciences, New College of Florida, Sarasota, FL 34243, USA

^* Author for correspondence (e-mail: dcolbert{at}aza.org)

Accepted 2 April 2009

The absolute sound localization abilities of two Florida manatees (Trichechus manatus latirostris) were measured using a four-choice discrimination paradigm, with test locations positioned at 45 deg., 90 deg., 270 deg. and 315 deg. angles relative to subjects facing 0 deg. Three broadband signals were tested at four durations (200, 500, 1000, 3000 ms), including a stimulus that spanned a wide range of frequencies (0.2–20 kHz), one stimulus that was restricted to frequencies with wavelengths shorter than their interaural time distances (6–20 kHz) and one that was limited to those with wavelengths longer than their interaural time distances (0.2–2 kHz). Two 3000 ms tonal signals were tested, including a 4 kHz stimulus, which is the midpoint of the 2.5–5.9 kHz fundamental frequency range of manatee vocalizations and a 16 kHz stimulus, which is in the range of manatee best-hearing sensitivity. Percentage correct within the broadband conditions ranged from 79% to 93% for Subject 1 and from 51% to 93% for Subject 2. Both performed above chance with the tonal signals but had much lower accuracy than with broadband signals, with Subject 1 at 44% and 33% and Subject 2 at 49% and 32% at the 4 kHz and 16 kHz conditions, respectively. These results demonstrate that manatees are able to localize frequency bands with wavelengths that are both shorter and longer than their interaural time distances and suggest that they have the ability to localize both manatee vocalizations and recreational boat engine noises.

Key words: audition, Sirenian, hearing, spatial hearing

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