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Blue whale males now singing bass, say scientists

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The songs of blue whales around the world have become significantly less high-pitched over the last 40 years, according to scientists. Boffins analysing the trend believe it may be to do with an increase in whale populations following the international ban on commercial whaling.

The shift from piping treble to rumbling bass is apparently well documented.

"The basic style of singing is the same, the tones are there, but the animal is shifting the frequency down over time. The more recent it is, the lower the frequency the animal is singing in, and we have found that in every song we have data for," says Professor John Hildebrand of the Scripps Institution of Oceanography.

Nobody really knows why whales sing - conceivably they're just humming to themselves as they go about their business - but it is believed that only the males do it, leading scientists to theorise that the songs are to do with finding mates and/or showing off to rival cetacean studs.

As a blue whale belts out his latest number, various factors affect the distance over which a potential ladyfriend (or rival) might hear it. In general, low-frequency sounds travel further under water: but a whale's song becomes less loud as the frequency drops, and according to Hildebrand and his colleagues this is the dominant factor. The basso songs of today are shorter-ranged than the higher-pitched ones of four decades ago, when the first recordings were made.

Various reasons for this were considered, including climate change and increases in ocean noise made by human activities. However the scientists think that with other whales now likelier to be nearby, the males no longer need to use the loud high-register songs.

"It may be that when (blue whale) densities go up, it's not so far to get to the closest female, whereas back when they were depleted it may have been that the closest female was a long way away," says Hildebrand.

The prof believes that whalesong pitch could furnish a handy indication of population levels. He and his colleagues have so far analysed only blue whales' songs, as they are the easiest to separate out, but they plan to go on and assess the music of other species next.

For the blue whale effort, the scientists analysed recordings from all the world's oceans, gathered over the last 45 years by scientific and military instruments deployed on the sea floor and afloat.

The US Navy, which provided many of the records from its seabed submarine-tracking network and sonar receivers, contributed funding for the research. Backing also came from the US National Oceanic and Atmospheric Administration and National Science Foundation.

There's more from Scripps here. ®

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