3 research outputs found
Sound Localization Abilities of Two Florida Manatees, Trichechus manatus latirostris
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
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Learning about Manatees: A Collaborative Program between New College of Florida and Mote Marine Laboratory to Conduct Laboratory Research for Manatee Conservation
Research with captive manatees initiated as part of a New College of Florida class project at MoteMarine Laboratory has yielded a wide range of research with substantive implications formanagement and conservation. Our training program directly supported investigations of bloodchemistry, immune function, stress-related physiology, respiration, thermoregulation, and behavioralecology. Our investigations of sensory processes included studies of visual acuity, color vision,passive and active touch, auditory frequency detection thresholds, auditory temporal processing rates,hearing in noise, and sound localization. Undergraduate and graduate students involved in thisprogram have been successfully mentored in sensory processes, animal behavior, and conservation.Further validation of the educational benefits of studying captive manatees awaits formal research onattitude, behavior change, and public policy related to protecting manatees and other marinemammals in natural settings
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Underwater Visual Acuity of Florida Manatees (Trichechus manatus latirostris)
In Experiment 1 underwater visual acuity was assessed in two Florida manatees, Trichechus manatus Latirostris , using grating stimuli in three conditions: Vertical gratings presented in freshwater, vertical gratings in saltwater, and horizontal gratings in saltwater. All stimuli were tested in a free-swimming format from a minimum distance of one meter. Substantial differences were found between the two subjects. One subject’s minimum angles of resolution (MAR) were 56 min for vertical stimuli in freshwater, 38 min for vertical stimuli in saltwater, and 24 min for horizontal grating stimuli in saltwater. When only trials under brightest light conditions were analyzed, MARs improved for vertical stimuli to 24 min in freshwater and 21 min in saltwater. No improvement was found for horizontal stimuli with brighter light conditions. The MARs of the second subject measured over a degree for all test conditions. In Experiment 2 only the first subject was tested from a closer viewing distance. He showed no improvement when allowed to approach targets to within 30 cm. The limited resolution of both subjects and absence of increased acuity at closer distances in one suggests that manatees use vision for intermediate or longer distance inspection of large objects. The disparity in visual resolution between subjects has possible implications for variability in acuity within the species