A mysterious noise coming from the Southern Ocean has puzzled researchers for over five decades. The curious quacking sound, nicknamed bio-duck, was first described in the 1960’s by submarine personnel. Since then it has been recorded at numerous locations across Antarctic waters, mainly during austral winter.

Until now nobody knew the source of this bizarre underwater quacking, and intriguingly it transpires that it’s coming from chattering Antarctic minke whales, according to a study published in the Royal Society journal Biology Letters.

Just over a year ago, scientists attached acoustic recording tags to two Antarctic minkes in Wilhelmina Bay. The whales were within large groups of between 5 and 40 other minkes, giving them plenty of opportunity to investigate their nattering, which had never been done before. Vocalizations from the whales were recorded by the device and analyzed by the team, who then used them for comparison with previous bio-duck recordings.

They found that the vocalizations were very similar to the previous recordings in terms of frequency and number of pulses. Given that the source of the vocalizations was within one to two body lengths of the acoustic device, they concluded that their results unequivocally demonstrate that the enigmatic bio-duck sounds were indeed produced by minke whales.

Not only have these results laid decades of mystery to rest, they also provide a unique opportunity to backtrack on years of recordings and use them to explore migration patterns of these whales. So far the recordings indicate that while some minke whales may remain in ice-covered waters all year, some migrate seasonally to lower latitudes. The team also believe that they may be able to utilize the recordings to estimate the abundance of minkes in these waters. They also provide a means to divulge information on the behavior of this so far poorly understood species.