10 December 2009
Scientists ponder global change in whale song
by Kate Melville
The pitch of the songs that blue whales sing across vast expanses of ocean to attract mates has been steadily creeping downward for the past few decades and scientists think it may indicate that numbers of the endangered marine mammal are increasing.
The researchers, from WhaleAcoustics, Scripps Oceanography and the Southwest Fisheries Science Center, said the downward curve in the pitch of the songs has been tracked in blue whales across the globe, from off the Southern California coast to the Indian and Southern Oceans.
"The basic style of singing is the same, the tones are there, but the animal is shifting the frequency down over time. The more recent it is, the lower the frequency the animal is singing in, and we have found that in every song we have data for," said Scripps' John Hildebrand.
While the function of blue whale songs is not known and scientists have much more to learn, they do know that all singers have been determined to be males and that the high-intensity, or loud, and low-frequency songs propagate long distances across the ocean. Blue whales are widely dispersed during the breeding season and it is likely that songs function to advertise which species is singing and the location of the singing whale.
The researchers speculate that in the heyday of commercial whaling, as blue whale numbers plummeted, it may have been advantageous for males to sing higher frequency songs in order to maximize their transmission distance and their ability to locate potential mates. But as population sizes have increased, it may now be more advantageous for males to sing songs that are lower in frequency rather than louder. "When they make these songs they need to use most of the air in their lungs," said Hildebrand. "It's like an opera singer that sees how long he can hold a note."
Reporting their work in the journal Endangered Species Research, the scientists suggest that the same downward pitch phenomenon may be true in other whales such as fin and humpbacks. Hildebrand adds that such knowledge about whale songs could be important in monitoring whale populations and recovery efforts.
Source: Scripps Institution of Oceanography