Odontocete hearing: Effects of noise and measurement during echolocation.

Abstract

Noise that interferes with active echolocation can come from either outside sources or be self‐generated. Our work on temporary threshold shifts has shown that either lower levels of anthropogenic noise presented for long time periods or intense sonar pings for short time periods can produce temporary reduction in sensitivity and temporary threshold shifts. Intense anthropogenic sounds intended to disrupt echolocation can also reduce echolocation performance. Our measurements of hearing during echolocation have shown that self‐generated intense outgoing signals are managed by the whale’s auditory system by (1) the use of forward masking as an automatic gain control system, (2) anatomical (or neurological) damping of outgoing signals, and (3) active manipulation of sensitivity levels of over all hearing. These processes of hearing allow the whale to adjust its hearing during echolocation to maximize the hearing of echoes. Measurements of hearing while a false killer whale actively echolocated, by measuring auditory evoked potentials, showed that the whale heard returns from a small cylinder better than it heard its own outgoing 180‐dB clicks that produced the echo returns from the cylinder. Interactions between outside anthropogenic noise and the hearing of self‐generated intense sounds during echolocation remain largely unexplored.