Sound Localization Abilities of Two Florida Manatees, Trichechus manatus latirostris

Abstract

Florida manatees (Trichechus manatus latirostris) live in the shallow, often turbid inland and coastal waters of the southeastern United States. Since their vision is poor (Bauer et al., 2003), other senses probably guide orientation. Previous studies have found that manatees can hear over 40 kHz (Gerstein et al., 1999) and have the capacity for rapid auditory temporal processing (Mann et al., 2005). However, it is not known if manatees have the ability to localize underwater sounds. Two Florida manatees were trained to identify underwater sound source locations using a four-choice discrimination paradigm. Three broad-band signals ( 0.2 - 20, 6 - 20, and 0.2 – 2kHz) were tested at four durations (3,000, 1,000, 500, and 200ms) and two tonal signals (4 and 16kHz) were tested with a 3,000ms duration. A total of 1,008 test trials were analyzed per subject. Both manatees learned the task easily, and could localize all of the test signals at a performance rate well above the 25% chance level. Within all of the broad-band conditions, performance accuracy ranged from 93% - 79% for Buffett, and 93% - 51% for Hugh. Broad-band signal duration did not have an effect on performance accuracy with Buffett who ranged from 89% to 87%, but did with Hugh who ranged from 87% - 58%. Broad-band frequency type did not have an effect on performance accuracy with Buffett who averaged 90%, 86%, and 89%, ix but may have with Hugh who averaged from 76%, 68%, and 65% at the 0.2 – 20, 6 – 20, and 0.2 – 2 kHz conditions. Both animals performed above chance levels with the pure tone signals, but at a much lower accuracy rate with Hugh at 49% and 32% and Buffett at 44% and 33% with the 4 kHz and 16 kHz conditions. Results from this experiment provide information about the manatees’ ability to localize different types of sounds in a controlled environment. This knowledge is important for understanding how manatees detect and localize noise generated from conspecifics and boat engines and contributes to making competent conservation management decisions about these endangered marine mammal