Thaindian News

Copenhagen, May 9 (IANS) Though they evolved separately over millennia in different worlds of darkness, bats and toothed whales use surprisingly similar acoustic behaviour to locate, track, and capture prey using echolocation, the biological equivalent of sonar.

Now, thanks to new technology that records what a whale hears as well as how it moves in the ocean deep, Peter Teglberg Madsen of Denmark’s Aarhus University and Annemarie Surlykke of the University of Southern Denmark have uncovered more similarities in the animals’ acoustic tactics.

Bats increase the number of calls per second (what researchers call a “buzz rate”) while in pursuit of prey. Whales were thought to maintain a steady rate of calls or clicks no matter how far they were from a target, according to Aarhus and Annemarie statement.

But the new research shows that wild whales also increase their rate of calls or clicks during a kill and that whales’ buzz rates are nearly identical to that of bats, at about 500 calls or clicks per second.

“On a purely physical basis, you would predict that whales and bats would operate at different [echolocation] rates and frequencies,” Madsen says. “But instead, they operate at the same rates and frequencies.”

The similarities support the idea that the acoustic behaviour of bats and whales may be defined by the auditory processing limitations of the mammalian brain.

Bats and toothed whales (which include dolphins and porpoises) had many opportunities to evolve echolocation techniques that differ from one another, since their nearest common ancestor was incapable of echolocation.

Nevertheless - as scientists have known for years - bats and toothed whales rely on the same range of ultrasonic frequencies, between 15 to 0 kilohertz, to hunt their prey. (For comparison, the human hearing range is between 20 hertz to 20 kilohertz.)

This overlap in frequencies is surprising because sound travels about five times faster in water than in air, giving toothed whales an order of magnitude more time than bats to make a choice about whether to intercept a potential meal.

These findings will be presented at the Acoustics 2012 meeting in Hong Kong, May 13-18, a joint meeting of the Acoustical Society of America (ASA), Acoustical Society of China, Western Pacific Acoustics Conference, and the Hong Kong Institute of Acoustics.