Dolphins bray when chasing down a fish

An array of underwater microphones has allowed the first analysis of which dolphin is doing the talking.

The work suggests that a blurt of low-frequency sound described as a bray might be a hunting call, reports Vincent Janik, now at the Woods Hole (Mass.) Oceanographic Institution.

Janik’s startling imitation of the sound explains the nickname for the donkeylike noise, very different from dolphins’ clicks and high-pitched whistles. Researchers had once speculated that such an oddball noise might be a weapon. One old experiment determined the sound level needed to kill a guppy, but braying a fish to death turned out to be ridiculously hard. However, Janik speculates that a nonfatal bray might startle prey into freezing for a vital instant.

In the new experiments at Mornay Firth, Scotland, Janik could usually trace braying to a dolphin zooming underwater as if chasing fish, he reports in May 7 Proceedings of the Royal Society of London B. The sound was so near the threshold of dolphins’ hearing that he speculates it’s unlikely to have evolved as a “Hey, Come chase the fish” summons. Instead, he says he suspects that braying attracts other dolphins much as a distant gunshot perks up deer hunters.