Wednesday, 1 April 2015

Porpoises use ‘sound searchlight’ to track down prey

March 31, 2015

Chuck Bednar for – @BednarChuck

When hunting, porpoises have the ability to switch their echolocation beam from a wide field to a narrow one and vice versa, researchers from Aarhus University in Denmark reported in a study published earlier this month in the journal eLife.

According to BBC News, the research reveals how the aquatic mammals (as well as their cousins the whale and the dolphin) send out a series of clicking and buzzing noises, then honing in on the echoes given off by their would-be prey. Essentially, they can fine-tune their sound beams like a flashlight to trap a fish and prevent it from escaping, the UK media outlet added.

“Toothed whales use sonar to detect, locate, and track prey,” the study authors wrote. “They adjust emitted sound intensity, auditory sensitivity and click rate to target range, and terminate prey pursuits with high-repetition-rate, low-intensity buzzes.”

“However, their narrow acoustic field of view (FOV) is considered stable throughout target approach, which could facilitate prey escape at close-range,” they added. “Here we show that, 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.”

They studied video, MRI, and acoustic-tag recordings and found that the flexibility of this sonar beam is modulated to accommodate changing spatial relationships with their prey, as well as the acoustic complexity of their surroundings. While whales and bats generate and transmit sounds using different techniques, researchers explained that both creatures can adaptively change their FOV, indicating that this trait played an important role in the evolution of echolocation.

Danuta Wisniewska of Aarhus University told BBC News that she and her colleagues hope that uncovering these acoustic secrets could help them develop a way of keeping porpoises and other types of toothed whales from becoming trapped in fishing nets.

The research was conducted using harbor porpoises in a semi-natural enclosure at a conservation research facility in Denmark. At the center, the creatures still had access to the seafloor, and the only thing separating them from a nearby harbor is a net. Fish were able to enter the area so that the porpoises could continue to hunt while the scientists monitored their activity.

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