THEY CAN ADJUST THE BEAM AS THEY ZERO IN ON PREY
Dolphins swim by a boat off Caye Caulker, Belize.
Porpoises have the amazing ability to not only locate prey with a beam of sound, but adjust the field of clicks and buzzes as they move in for the kill, preventing the fish from slipping away, a new study finds. The lead researcher from Denmark's Aarhus University tells the BBC that the switch is much like adjusting a flashlight. If you're looking for your car in a parking lot, "you could use a narrow beam over a long distance and still see a lot," she says. "But when you're trying to get your keys into the car, you would switch to a wider beam. This is similar to what we see in porpoises." The beam is controlled by a fatty structure in the porpoise's head called the melon.
"Like some bats, harbor porpoises can broaden their biosonar beam during the terminal phase of attack but, unlike bats, maintain the ability to change beamwidth within this phase," the researchers write in the journal eLife. The team, which studied harbor porpoises in a semi-enclosed research facility that gave the animals seafloor access, believes other dolphins and whales have the same sonar ability. The lead researcher tells the BBC that the discovery suggests many porpoises end up in fishing nets because of "attention blindness" that causes them to ignore potential hazards as they zero in on a fish. (Porpoises in San Francisco Bay face another hazard: gangs of angry young dolphins.)