Blue Whales Sing at Same Pitch, Study Says
for National Geographic News
Luciano Pavarotti they're not, but if blue whales ever build up a repertoire they could give the Italian opera singer a run for his money. The cetaceans have perfect pitch. So perfect, in fact, that it's impossible to tell individuals apart from their calls.
"You might think that a big whale makes a lower sound than a small whale—they come in all different sizes—but they all make the same pitch," said Roger Bland, a physicist at San Francisco State University in California.
Bland, who took an active interest in underwater acoustics 12 years ago as a way to spend more time with his water-loving kids, would like to figure out how to tell individual blue whales (Balaenoptera musculus) apart from their calls.
Such an identification mechanism may allow conservationists to keep better tabs on blue whale populations, but so far the task has proven fruitless.
John Hildebrand, an expert on marine, mammal acoustics at the University of California San Diego's Scripps Institution of Oceanography in La Jolla, said Bland's finding correlates with his own observations.
"The whales clearly work to synchronize the frequency of their calls," he said. "They must do this despite a range of sizes of animals."
Bland and colleague Newell Garfield based their research on analysis of blue whale sound recordings captured with hydrophones (devices for detecting sound transmitted through water) on top of a seamount 60 miles (95 kilometers) offshore from Half Moon Bay, California. (See sidebar.)
Since the researchers only hear and see the sounds as played back over a sonogram (a device for visualizing sounds), they're not certain as to which or how many whales are responsible for the calls they detect.
"Some biologists are skeptical that we are listening to more than one whale, but I think there is enough information to make it clear that it is different whales at the same pitch," Bland said.
Bland and Garfield often detect overlapping patterns of the two distinct blue whale calls: the A call and B call. This overlap indicates the presence of more than one whale. The A call is a series of short pulses that sounds like a person gurgling mouthwash and the B call is a long, low groan.
The A call usually precedes the B call, but sometimes only the B call is heard. "If we keep at it long enough, we could find that the thing that distinguishes individuals is small variations in the pattern, but at the moment we've only got the pattern," Bland said.
The B call is simpler and easier to analyze. According to Bland, the B calls off Half Moon Bay are at a frequency of about 16 hertz, with no detectable variation between individuals. The researchers have not scrutinized the more complex A call in detail but say it too shows little variation.
In an attempt to get more detail on what blue whales are making the calls and why, John Calambokidis, a whale expert with Casacadia Research in Olympia, Washington, and colleagues with the Scripps Institution of Oceanography and the National Geographic Society are attaching acoustic and video tags to individual whales.
After recording data for several days, the tags detach from the whales and float to the surface, where they are collected by researchers and analyzed.
"One thing we find is that predominantly, if not solely, males are producing the calls," Calambokidis said. In addition, although there is no variation in the pitch of the calls among individuals in a population, the calls do vary among different populations around the globe.
"This may argue against this as some ideal frequency and argue maybe for males using it for advertising to other females or to other males related to reproduction," he said.
For example, males may all be trying to make the same low frequency call as a way to indicate their fitness. Any male that deviates from this frequency would not be considered a good mate and thus rejected, Calambokidis said.
Hildebrand and his colleagues also suggest that blue whale calls are related to mating. According to their theory, the whales make their calls as loud and at as low a frequency as they can. Loud calls travel further, and low frequency may be a desirable trait.
"Of any animal on the planet, the largest—blue whales—will surely have a mechanism to select large animals for breeding. Large animals have large lung volume and can therefore make high-intensity and low-frequency calls," Hildebrand said.
Interestingly, Hildebrand's research also suggests that the blue whale call has been getting lower in pitch over the past 20 to 30 years by about one-half hertz each year. "The cause is controversial, but I think it is a response to recovery from commercial whaling," he said.
Calambokidis said the available information on historical and current blue whale populations is imprecise, but that at the end of the 19th century, the global population was estimated at 300,000. By the time blue whale hunting was banned by the International Whaling Commission in 1966, that figure may have dropped to as low as 10,000.
Today some scientists believe blue whale populations are even lower. Conservationists are keen to keep close tabs on the cetaceans to determine if populations are recovering.
Bland's hope is that identifying individual blue whales from their calls could help conservationists with their monitoring activities. But since only males appear to be making the calls, trying to take a census of the population from calls alone is a difficult task, Calambokidis said.
Further complicating matters, only a small percent of the males in any group are responsible for the majority of the calls according to Calambokidis. In a group of ten whales out feeding, none might be calling whereas one, isolated male might call over and over.
"There's not a good correlation between the number of whales seen in an area and the number of calls being heard," Calambokidis said. "If you hear calls, there is at least 1, but trying to say 1 or 50 is not an easy thing to do."
Calambokidis added that if whale acoustic researchers can determine how to distinguish individuals from their calls, the information combined with better understanding of behavioral data may eventually yield a good method for tracking populations.