Do manatees utilize infrasonic communication or detection

Some researchers speculate Sirenians might utilize infrasonic communication like their distant elephant cousins; however, audiogram measurements and calibrated manatee vocalizations do not support this contention. A comprehensive series of hearing tests conducted with West Indian manatees yielded the first and most definitive audiogram for any Sirenian. The manatee hearing tests were also the first controlled underwater infrasonic psychometric tests with any marine mammal. Auditory thresholds were measured from 0.4 to 46 kHz, but detection thresholds of possible vibrotactile origin were measured as low as 0.015 kHz. Manatees have short hairs on their bodies that may be sensitive vibrotactile receptors capable of detecting particle displacement in the near field. To detect these signals the manatee rotated on axis, exposing the densest portion of hairs toward the projector. Manatees inhabit shallow water where particle motion detection may be more useful near the water’s surface, where sound pressures are ...