Manatees masked thresholds for complex sounds

Acoustical masked thresholds of complex real world sounds were measured with West Indian manatees. Motor boat and species‐specific calls were recorded, filtered and played back in a forced‐choice two‐alternative test. A method of constant stimuli was used to estimate the 50% detection thresholds of peak spectral components. Both white noise and recorded wild ambient spectra were used as continuous background noise for two sets of threshold estimates. Manatee calls were detected at and within both white noise and wild ambient levels. Thresholds for broadband boat noise ranged from 9 to 29 dB above ambient conditions. Thresholds for idling boat noise were the highest. The levels were consistent with the subjects’ auditory limits for the lower frequencies with the spectra. The manatee is well adapted to hear the species specific vocalizations under noisy conditions. The integration of multiple critical bands may result in loudness summation benefits which manatees can exploit at higher frequencies, however, ...