Abstract:
The echolocation events of free-ranging harbor porpoises, a bottlenose dolphin, and a baiji were observed by a compact acoustic signal detector (click light) and a hydrophone (B&K8103). The click light harnessed on a dolphin with a hydrophone above the melon of the dolphin lit at every detection of echolocation events. It was assumed that a series of pulses corresponded to an echolocation event. The hydrophone beside a tank could also receive echolocation events from the dolphins. Echolocation events from two harbor porpoises kept in a tank and in a net enclosure were observed by the click light. The bottlenose dolphin with the click light was kept in a circular pool. The echolocation events from the baiji were observed by a hydrophone beside a pool of the Institute of Hydrobiology in China. The echolocation events per minute (echolocation rate) ranged from 0 to 25. The echolocation rate changed frequently for all three species. The dolphins could be swimming without echolocating for a few minutes. Feeding induced higher echolocation rates. Enclosure types and human disturbances during experiments also affected the echolocation rates. Visual deprivation for the bottlenose dolphin or a dark condition for the harbor porpoises significantly increased the echolocation rates.