A study in the journal Endangered Species Research, has found male blue whales all over the world have lowered their tone. Mark McDonald of WhaleAcoustics first noticed the change about eight years ago when he had to shift automated blue whale song detectors off California to lower frequencies.
He decided to compare the songs in areas ranging from the North Atlantic to the Indian Ocean with the help of researchers from the Scripps Institution of Oceanography in California.
They found all the studied whales had dropped their voices although the range varied. Blue whales in the northeast Pacific population lowered their voices the most with a drop of 31 per cent between 1963 and 2008. This is the same as three white keys on the piano.
John Calombokidis, a blue whale expert at the Cascadia Research Collective, said: 'It's a fascinating finding. It's even more remarkable, given that the songs themselves differ in different oceans. There seem to be these distinct populations, yet they're all showing this common shift.'
Blue whales migrate over large distances and produce songs throughout the year, there are around 10,000 living in the wild. The singers have always been found to be males traveling at relatively high speeds but why their voices have lowered is a mystery.
Mr McDonald said one theory was the impact of an increasingly noisy ocean. But he said if blue whales are struggling to make themselves heard over the sound of marine traffic, their voices should become higher, rather than lower.
It has also been suggested that climate change has led to the seas becoming more acidic and lowered voices could travel better in these waters. However, scientists said this still doesn't explain the extent of the drop.
The favoured theory is that males do not have to call as loudly to be heard by females because their numbers are slowly increasing following a whaling ban in 1966.
Mr Calambokidis added that females could find the deeper tones more appealing.
'The males produce the calls so they are related to reproduction,' he said, 'not prey or navigation.'
It seems that every nature-related article now has to invoke the religion of climate change at some point to be seen as politically correct.