Scientists unravel mystery of bizarre 'bio-duck' sound

Birds chirp, lions roar, and, according to new research, minke whales quack.

That's what scientists learned when investigating an oceanic sound that had puzzled researchers for decades.

Lead researcher Denise Risch, of the US National Oceanic and Atmospheric Administration;s Northeast Fisheries Science Center in Massachusetts, says that the mysterious sound was first described in the 1960s by submarine personnel, who dubbed it "bio-duck."  

Some speculated that the sounds, which had a vaguely mechanical sound to them and were heard at fixed intervals, were produced by other submarines, or perhaps by some species of fish.

In the following years, some suggested that the sounds could have been produced by minke whales, a name given to two species of small baleen whales, but there was no way to confirm it.

In this research, Dr. Risch and her colleagues, confirm that the "bio-duck," a sound in the range of 100-200 Hz recurring every 3.1 seconds, is indeed produced by the whales. In February last year, the team tagged two minke whales off Western Antarctica using suction-cup tags fitted with tiny computers and underwater microphones.

After analyzing previous recordings and interpreting acoustic recordings from this experiment, Risch recognized two different kinds of low frequency sounds--one was the downward-sweeping sounds already identified by researchers in the 1970s, and the other was the quack-like sound which had baffled researchers for many years. Both produced by minke whales along with other sounds.

The scientists' research yielded new data about the whales' migration patterns. Previous research revealed that the bio-duck sound could be heard during winter in two different regions – Western Australia and Antarctica. This suggests that not all Antarctic minke whales migrate to Western Australia for breeding during the winters each year. Some of them, it seems, remain in  Antarctic waters while the rest migrate.

At this point scientists do not know if the sound is produced by both males and females, and they don't know the sound's purpose. Researchers speculate that it could help the ice-loving whales navigate, or perhaps it could be a mating call.

The sceintists' findings have been published in a paper titled "Mysterious bio-duck sound attributed to the Antarctic minke whale (Balaenoptera bonaerensis)," in the Royal Society journal Biology Letters.