ATLANTIC BOTTLENOSE DOLPHINS USE DUAL-COMPONENT BIOSONAR FOR ECHOLOCATION

For visual animals, it's hard to understand how echolocating creatures perceive the world. Yet dolphins successfully hunt and communicate through a system of clicks and high-pitched whistles. So what do these echolocation calls sound like to dolphins? Songhai Li, Paul Nachtigall and Marlee Breese tested the hearing of an Atlantic bottlenose dolphin named BJ as she listened to echoes of her own echolocation clicks reflected from various sized cylinders placed 2–6.5 m in front of her nose (p. 2027). Recording BJ's electrical brain responses with a suction-cup recording electrode just behind her blowhole, they could see that the echoes and calls both triggered brain activity, although the responses to the echoes were weaker. The team also saw that the responses to the fainter echoes became stronger as the objects became more distant, ‘Demonstrating an overcompensation of echo attenuation,’ they say. And when the team measured the strength of the dolphin's echolocation clicks, they found that calls became louder as the cylinders became more distant. The team says, ‘The results demonstrate that a dual-component biosonar control system formed by intensity compensation behaviour in both the transmission and receiving phases of a biosonar cycle exits synchronously in the dolphin biosonar system.’