Blue whales are changing the pitch of their songs almost a whole tone, according to a new study published in the Journal of Geophysical Research: Oceans.
The global decline in the pitch of whale songs has been a mystery, with chief suspects being the increase in ocean noise from shipping, submarines and underwater resource exploration. The new study, however, suggests other factors may be behind the trend.
The researchers found that a seasonal variation to Antarctic blue whales’ pitch correlates with breaking sea ice in the southern Indian Ocean, suggesting that seasonally they’re laboring to make their voices heard above the crackling and grinding sounds of breaking ice.
Only male blue whales sing, and their hums can be about as loud as large ships. A single blue whale’s sounds can travel for 600 miles underwater, enabling whales to communicate with one another across long distances.
The paper analyzed more than 1 million songs from three species of large baleen whales: fin, Antarctic blue and three acoustically distinct populations of pygmy blue whales.
Six stationary underwater microphones recorded the calls over 6 years, from 2010 to 2015, in the southern Indian Ocean, an area spanning 3.5 million square miles.
The study’s authors analyzed the pitch of selected elements of each species’ song.
Between 2002 and 2015, the pitch of blue whales’ calls had fallen by “about a whole tone or major second interval in Western music tradition,” the press release states.
This trend is intriguing, but has not yet had major consequences.
The fact that the pitch drop was observed in the southern Indian Ocean, where ship noise has decreased in recent years, suggests an uptick in global ocean noise is not the cause of the downward trend in whale pitches.
Instead, increasing blue whale populations could be resulting in a natural shift in volume, since whales may not need to sing as loudly to reach another whale.
“They can decrease their call intensity to keep in touch, because there are more whales,” Emmanuelle Leroy, lead author of the new study and a research fellow at the University of New South Wales in Australia, said in a press release. “These calls are long distance communication.”