Blue whales are changing their tune. That's what new recordings of these huge mammals indicate. This changing behavior is described in an article in the journal Endangered Species Research. Why it's happening is unknown. But one theory says they're singing in lower tones today because the species is coming back.
Stand on the beach in San Diego and it's unusual but 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's a professor at the Scripps Institution of Oceanography, and he studies the sounds of dolphins and whales.
Hildebrand co-wrote the article, mentioned above, on the songs of male blue whales. He said the males sing in order to warn away other males and to attract females. But their song has been changing.
"They've been shifting the frequency, they've been shifting the pitch, to be lower each year," said Hildebrand. "And that shift in pitch has resulted in song that is now about 30 percent lower than it was in the 1960s."
Hildebrand said this change in register is happening in blue whale colonies all over the world. But why? The theory of Hildebrand and his co-authors is tied to the good news that blue whales are coming back from the brink of extinction. Blue whale hunting was internationally banned in 1966. But Hildebrand said prior to that whaling had reduced the number of these creatures to dangerously low levels.
"Worldwide in the early sixties there probably would have been, you know, a few thousand," he said.
Those low numbers meant much lower densities of blue whales, and fewer females who could hear a male's come-hither song. Hildebrand said, for males in that situation, "There's a push to have the sound go to higher frequency so that more of the girls can hear it."
In other words, in the sixties the girls were so far away the guys had to shout to be heard. But now that blue whales are more numerous, Hildebrand speculates that males have abandoned the tenor register and returned to singing bass, because it makes them sound bigger and more attractive to females. He said males of many species use lower tones to attract mates.
"In fact, human females, if you put some headphones on and play a bunch of males voices and you tell them 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," Hildebrand said.
No one disputes the finding that blue whale song has gone down in pitch. But Hildebrand's theory of why it's happened has raised some doubts and some eyebrows.
"It's a great anthropomorphism to suggest that the whales have thought this through and have to modify their behavior," said whale expert Richard Ellis of New York's Natural History Museum.
"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," said Ellis.
Still, Hildebrand said blue whales are conformist when it comes to behavior. And if a few males realize they can utter deep sexy tones and still be heard by the females, other males are likely to follow suit.
