LA JOLLA, Calif., Dec. 3 (UPI) -- Researchers in California say the voices of male blue whales have gotten lower by 31 percent since the 1960s, although the reasons why aren't clear.
Mark McDonald of WhaleAcoustics, which conducted the study with researchers from the Scripps Institution of Oceanography in La Jolla, Calif., reported in the journal Endangered Species Research that recording devices off California had to be adjusted to capture the lower frequency calls.
McDonald told the Victoria (British Columbia) Times-Colonist one theory is that increasing noise in oceans from ships has led to the lower frequency calls.
"If it dropped 50 percent it would be down an octave," he said.
However, John Calambokidis, director of Cascadia Research in Olympia, Wash., disagreed, saying he believes female whales find the lower calls more appealing..
"The males produce the calls, so they are related to reproduction, not prey or navigation," he said.
Recorded blue whale calls can be heard at the National Oceanic and Atmospheric Administration Web site www.pmel.noaa.gov/vents/acoustics/whales/bioacoustics.html.