TARGET DISCRIMINATION BY AN ECHOLOCATING FINLESS PORPOISE, NEOPHOCAENA PHOCAENOIDES

The ability of a finless porpoise (Neophocaena phocaenoides) to discri minate the material and size of a target by echolocation was investiga ted. The porpoise was required to choose a standard target of a 15-mm diameter solid steel cylinder from two stimuli, a standard and a compa rison target, presented simultaneously. The porpoise could distinguish a standard cylinder from acrylic resin and brass targets, but had dif ficulties distinguishing it from an aluminum cylinder. In size discrim ination, the porpoise could distinguish the standard from 12-, 18-, an d 20-mm diameter cylinders, but had difficulties distinguishing it fro m a 14-mm diameter cylinder. Echo measurements suggest that the porpoi se is able to detect: (1) time difference between two echo highlights to within approximately 1 mu s, (2) frequency shifts of approximately 7 kHz in a broadband echo having a peak frequency of nearly 140 kHz, ( 3) time-separation pitch of approximately 30 kHz, and (4) target stren gth differences of approximately 1 dB.