![]() Those whales are the best-studied of all blue whale populations, and their song pitch has dropped by 31 percent since the late 1960s. west coast hasn't shown a dramatic upwards trend in numbers, but its pitch is declining," said Calombokidis. The population of blue whales off the U.S. "That's the first place to look for an answer, but it doesn't fit more-localized patterns. Now that there are more, they can lower their voices and their pitch.īut even in populations that escaped the carnage relatively unscathed, where population densities have remained steady, songs are getting lower. Maybe songs were higher-pitched when recording started, because the whales had to sing extra-loud in order to reach their scattered brethren. It's only since hunting ceased that they've been recorded. "But those factors are so small, and this is such a huge shift in frequency," said McDonald.Īnother explanation involves the recovery of blue whale populations, which were nearly hunted to extinction during the first half of the last century. It's also possible the whales are responding to changing dynamics in how sound travels through water that's become warmer as Earth heats up, absorbing more carbon dioxide and growing more acidic than before. But if whales were trying to be heard above the din, they'd sing at higher rather than lower pitches, said McDonald. Ambient ocean noise has increased by more than 12 decibels since the mid-20th century. There seem to be these distinct populations, yet they're all showing this common shift."Īccording to McDonald, the first explanation to come to mind involved noise pollution caused by increased shipping traffic. ![]() ![]() "It's even more remarkable, given that the songs themselves differ in different oceans. "It's a fascinating finding," said John Calombokidis, a blue whale expert at the Cascadia Research Collective. Their analysis, published in October in Endangered Species Research, shows that the songs' tonal frequency is falling every year by a few fractions of a hertz. Since then, he and Scripps Institution of Oceanography researchers Sarah Melnick and John Hildebrand have gathered thousands of blue whale recordings made since the 1960s, spanning populations from the North Atlantic to the South Pacific to the East Indian Ocean. ![]()
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