Science

blue whale, blue whales
National Oceanic and Atmospheric Administration/AP
This undated photo provided by the National Oceanic and Atmospheric Administration shows
blue whales in the Gulf of the Farallones National Marine Sanctuary in California.

Blue Whales Singing at Ever-Lower Frequency

February 01, 2010 05:40 PM
by Colleen Brondou
Researchers can’t figure out why blue whales, the largest animals on Earth, are singing in deeper voices every year.

Blue Whales Change Their Tune

facebook
Around the world, blue whales are singing at a lower pitch and scientists “don’t have the answer” to explain why, Mark McDonald, president of Whale Acoustics, a company that monitors ocean noise, the impact of noise on whales and whale calls and songs, told Brandon Keim of Wired magazine.

McDonald and his associates first discovered the change in the whales’ song eight years ago. In order to capture the changing sound of the whales over the years, scientists had to keep recalibrating the detectors to recognize the lower frequency. McDonald, along with Sarah Melnick and John Hildebrand of Scripps Institution of Oceanography, has gathered blue whale recordings made since the 1960s, from whale populations all over the world. Their work “shows that the songs’ tonal frequency is falling every year by a few fractions of a hertz,” Keim writes.

“It’s a fascinating finding,” John Calombokidis, a blue whale expert at the Cascadia Research Collective, told Wired. “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.”

Opinion & Analysis: Why are blue whales singing in deeper voices?

One possible explanation for the change is the increase in noise pollution in our oceans. In 2008, the International Fund for Animal Welfare (Ifaw) argued that ocean noise from ships and other sources was interfering with marine mammals’ ability to communicate. But McDonald argues that if whales were trying to be heard through the noise, they would sing at higher pitchers rather than lower ones.

A change in population may be another explanation. Blue whales were hunted to near extinction at the first half of the 1900s, and they’ve been recorded only since hunting stopped. “Maybe songs were higher-pitched when recording started, because the whales had to sing extra-loud in order to reach their scattered brethren,” Keim writes. “Now that there are more, they can lower their voices and their pitch.”

But even in areas where the whale population hasn’t grown significantly, the songs are still getting deeper. “The population of blue whales off the U.S. west coast hasn’t shown a dramatic upwards trend in numbers, but its pitch is declining,” Calombokidis told Wired.

Others suggest that mating and sexual selection may be a factor. Only male blue whales sing, so researchers think that maybe the “larger, ostensibly more virile whales” are producing deeper songs, which the other males are trying to copy, “just as human guys might lower their voices when trying to impress a woman,” according to Wired.

Background: Humpback whales

In 2000, ABC News reported that Australia’s east coast humpback whales had stopped their own mating song and adopted a new song from a small group of whales visiting from the Indian Ocean.

“What is staggering is that all the males have switched to the new song which was brought over by a few ambassadors from the west coast,” Michael Noad, a marine scientist, told Reuters.

Humpback whale songs are quite varied and complex. The patterns are distinct to where the whale lives, and the songs are usually between seven and 15 minutes long, “and contain several themes like verses in human songs,” ABC News reports. Male humpback whales sing their songs to attract females during the mating season.

“The theory is the novelty of the new song is what made it popular,” Noad said. “Female whales hear the same song over and over again and get bored and disinterested in the males, so the males alter their songs slightly to stand out in the crowd.”

Recordings: Listen to whales

Wired magazine links to a recording of a blue whale song, and the Intersea Foundation has a selection of four recordings of humpback whales.

Related Topic: Birds change their songs

Whales aren’t the only ones changing their tunes; birds have also made adjustments to their songs. In May 2009, ScienceDaily reported that male white-crowned sparrows in California, Oregon and Washington had “lowered their pitch and slowed down their singing.” Elizabeth Derryberry, then a researcher at Duke University, found that birds living in areas that had been cleared sang slower and at a lower pitch once vegetation returned. The explanation? “A lower, slower song suffers less reverberation in denser foliage and will be heard more accurately,” ScienceDaily reported.

Like their country cousins, white-crowned sparrows in the city have also had to make changes to their song in order to be heard. In 2009, ABC Science reported that researchers David Luther and Luis Baptista looked at white-crown sparrows in the San Francisco area from the late 1960s to 1998. They found that as urban noise increased, so did the frequency of the birds’ song. “In response to high levels of low-frequency ambient noise, urban birds have songs with higher frequencies,” the researchers wrote.

Reference: Animal behavior

HowStuffWorks explains the basics of animal behavior, including social behavior in animals and how humans affect other animals.
facebook

Most Recent Beyond The Headlines