Since at least 1960, submarine personnel in Antarctic waters had been hearing a mechanical, repetitive quacking — pulses between 60 and 100 Hz arriving every 1.6 to 3.1 seconds. They named it the bio-duck. Acoustic researchers called it "one of the largest still unresolved mysteries of the Southern Ocean."
In the austral summer of 2013, marine biologist Denise Risch led a team that attached suction-cupped recording devices directly to two Antarctic minke whales using a pole from a boat. The devices collected sound, temperature, pressure, acceleration, and magnetic fields. Over 18 and 8 hours of recording, the whales made 32 calls, six of which matched pre-existing bio-duck recordings. No other marine mammals were within a kilometer. The source was Antarctic minke whales (Balaenoptera bonaerensis).
What the sound is for remains unknown. Researchers have linked calling activity to the diel vertical migration of krill — the whales' main food source — suggesting the calls may coordinate feeding. Others argue they may serve a mating function, since acoustic presence peaks during the whales' breeding season. The discovery is useful beyond the biology: bio-duck calls are now used to track minke whale migration and abundance in areas where sea ice makes conventional ship-based surveys nearly impossible.
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