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Researchers in San Diego say blue whales are singing a new song. They don't know why it's happening, but scientists report that blue whales are now singing half-octave lower than they did in the 1960s. From member station KPBS, Tom Fudge reports.

TOM FUDGE: Here on the coast of San Diego, it's not unheard of to see a spouting blue whale. The Eastern Pacific is one of a handful of areas where blue whales migrate and feed. Just a couple of blocks from here is the office of John Hildebrand. He is a professor at the Scripps Institution of Oceanography, and he studies the sounds of dolphins and whales.

Professor JOHN HILDEBRAND (Scripps Institution of Oceanography): So that's the pulse part.

(Soundbite of music)

Prof. HILDEBRAND: (Unintelligible)

(Soundbite of laughter)

FUDGE: That pulsing sound was one of the songs a male blue whale sings to warn away other males and to attract females, but Hildebrand says their song has been changing.

Prof. HILDEBRAND: They've been shifting the frequency. They've been shifting the pitch of the song to be lower each year. And that shift in pitch has resulted in a song that is now about 30 percent lower than it was in the 1960s.

FUDGE: Hildebrand says this change in register is happening in blue whale colonies all over the world. And he believes the change is tied to the elimination of blue whale hunting. Before hunting was banned in 1966, the numbers of blue whales were dangerously low.

Prof. HILDEBRAND: Worldwide in the early 60s, there probably would have been a few thousand.

FUDGE: Those low numbers meant there were few females available to hear a male's come-hither song. Hildebrand says for males in that situation...

Prof. HILDEBRAND: There is a push to have the sound go to higher frequency so that more of the girls can hear it.

FUDGE: In other words, the guys had to shout to be heard. But now that blue whales are more numerous, Hildebrand thinks the males have gone back to singing bass because it makes them sound bigger and more attractive to females. He says males of many species use lower tones to attract mates.

Prof. HILDEBRAND: In fact, human females, if you put some headphones on and play a bunch of male voices and you say I want you to pick out the sexy voice, do they pick the weak little voice or do they pick the big booming voice? Right? I mean, you know the answer.

FUDGE: No one disputes the finding that blue whale song has gone down in pitch. But Hildebrand's theory of why it's happening has raised some eyebrows.

Mr. RICHARD ELLIS (Natural History Museum, New York): It's a great anthropomorphism.

FUDGE: Richard Ellis is a whale expert at New York's Natural History Museum.

Mr. ELLIS: I really don't think that the whales - for all their big brains and everything else - I really don't think the whales think about this.

FUDGE: Still, if a lower tone becomes an advantage to some males, Hildebrand says it will be copied by others. His article is published in the journal Endangered Species Research.

For NPR News, I'm Tom Fudge in San Diego.

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