Blue whales have changed their songs.
It’s the same old tune,
but the pitch of the blues is mysteriously lower — especially off the
coast of California where, local researchers say, the whales’ voices
have dropped by more than half an octave since the 1960s.
No one
knows why. But one conjecture is that more baritone whales indicate
healthier populations: The whales may be less shrill because they’re
less scarce and don’t have to pipe up to be heard by neighbors.
The
discovery was accidental. Whale acoustics researcher Mark McDonald was
trying to track blue whales’ movements using data from Navy submarine
detectors. He had created a program to filter out the blues’ songs from
a din of ocean noise captured by these instruments.
But he kept having to rewrite the code. Each year, it seemed, the whales sang at a lower pitch.
At
first, the researchers thought it was a quirk. But after a couple of
years of adjusting for lower frequencies, "we knew there was something
strange going on," said John Hildebrand, an oceanographer at Scripps
Institution of Oceanography in San Diego and co-author of the study published recently in Endangered Species Research.
So the researchers scoured military data and seismograph readings for clues about what blue whales used to sound like.
A
retired Navy scientist directed Hildebrand to a trove of tapes stored
at Sea World. The delicate old reels were the size of dinner plates. It
turned out they contained snippets of blue whale songs from 40 years
ago.
The tapes eliminated all doubt: In the Beach Boys’ era,
blue whales’ voices, while nowhere near falsetto, had been distinctly
higher pitched.
With more work, the researchers were able show
that blue whales worldwide are using deeper voices lately. Some have
dropped their calls by only a few tones, but all showed a steady
decline. "It was baffling," Hildebrand said.
Blue whales are
shrouded in mystery as it is. Sleek, mottled and silvery, they are rare
and don’t reveal much. They don’t leap on the surface as much as
humpback whales do. They might, if really flustered, slap their tails
on the water. More often, they quietly sink, Hildebrand said.
Their song is barely audible to the human ear — a deep bass growl with very long wavelengths befitting very long whales.
The
tone is so deep that if played in a small room, it’s hard to hear: The
long-period sound waves extend beyond the walls. But play a recording
very loudly, in a large auditorium, and "you feel it in your chest as
much as you hear it," McDonald said. "It’s awesome."
The
researchers pondered possible causes. Warmer temperatures? More acidic
seas? Such factors affect the way sound moves through water, but not
enough to explain the change, Hildebrand said.
The rumble of
shipping traffic is thought to affect marine mammals. But the
researchers argue that if whales were just trying to be heard above the
fray, they would adopt higher, not lower, voices.
It’s also
possible that the low voice is just a fad. Biologists talk about whale
"culture," and blue whales tend to be conformists. But researchers have
said they doubt that a random, learned behavior could spread all over
the globe.
So they put themselves in the whales’ shoes. McDonald
surmised that whales would rather not sing in higher voices if they
didn’t have to. They prefer deep and manly — "a lower, sexier
frequency," he said.
Among whales, he said, depth of voice may
bespeak more desirable mates with larger bodies. It’s useful shorthand,
since it’s hard to get a good look at one’s suitor if he is 80 feet
long and swimming in murky water.
After the whales were hunted
nearly to extinction, they may have been spread so thin that they could
no longer find one another easily, prompting them to raise their pitch.
Efforts
to restrict whaling beginning in the late ’60s helped populations
rebound. With increased numbers, the whales may not have needed to
shout and may have gradually returned to their deep tones.
"This
hints that some of these great whales are recovering; it’s not all
doom," said co-author Sarah Mesnick, ecologist at the National Oceanic
and Atmospheric Administration Fisheries Service.
If whale songs
are related to population density, they might aid efforts to count blue
whales, Hildebrand said. They once numbered in the hundreds of
thousands. Today, their population is thought to be 10,000 or so.
Oceanographer
Jay Barlow, program leader at NOAA fisheries, cautioned that changes in
the whales’ pitch don’t track closely with population changes.
California blues, for example, recovered most strongly in the ’70s and
’80s, and their numbers may not have grown much since, he said.
But
Barlow had no alternate theory for the deeper songs, which he sometimes
plays on his home stereo. The sound makes his floor shake and upsets
his cats.
David Mellinger, a marine mammal bio-acoustician at
Oregon State University, said that, whatever the reason, the finding
"is astonishing." It recalled to him the first time he heard a blue
whale sing.
He was on a boat, using headphones, and one passed.
"It was a defining moment in my life," he said. "It made a visceral
impression on me. Just this huge animal. I could hear the hugeness of it."
— Jill Leovy
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Photo: A blue whale surfaces near Dana Point, Calif. Credit: Marc Carpenter / Associated Press