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| Earth on Aug 23, 2010

John Hildebrand on blue whale songs’ lower pitch

Blue whales are still endangered, but their population is rising. And that might explain why the pitch of their songs has gotten lower.

Blue whales are still endangered, but their population is rising. And that might explain why the pitch of their songs has gotten lower. That’s according to John Hildebrand, who studies whale songs at the Scripps Institution of Oceanography in San Diego. Dr. Hildebrand published a 2009 study on whale songs.

John Hildebrand: The animals had decreased their pitch of their songs about 30% from the 1960s to today.

The pitch got lower, Hildebrand believes, because there are more whales now than several decades ago. Whale populations were decimated in the 1960’s, due to over hunting. Since that time, whaling has been restricted, and populations have begun to recover. That affects their songs, said Hildebrand.

John Hildebrand: The hypothesis that we’re putting forward is that the shift downward in frequency is a response to the increasing population of the animals. As the densities go up, the distance to the closest females is shortened, so you don’t have to have a song in high amplitude.

In other words, whales don’t have to project their song as far in order reach a female, so they’ve literally changed their tune.

John Hildebrand: It may be that the female, when it’s within some range of the male, uses the song to assess the fitness for breeding.

To solve the mystery of the change in pitch, Hildebrand considered the whales’ history.

John Hildebrand: Blue whales in particular were commercially hunted. And their populations were taken down to a few percent of where they were originally.

He said the drastic and rapid reduction in the size of the whale population forced the whales to adapt their song to the new situation.

John Hildebrand: Imagine if 99 out of every 100 people were removed from the earth, there would be huge social adjustments. And I think the whales went through that same kind of thing.

He described the song as important to breeding – in other words, increasing the population.

John Hildebrand: Generally a song is made by a male who is trying to either attract a female or repel a competitor, another male.

Hildebrand said that when the population size increased, the rules of the game changed. Whereas in the 1960s, the advantage was for songs that could travel further through the ocean; today, the songs are meant to sound more impressive to a female.

John Hildebrand: It could be that the females are using simultaneously the pitch of the sound and the amplitude of the sound to judge the size of the male. Only a big male – one with a lot of air in his lungs – can make a sound that’s both low frequency and high in amplitude.

His study’s results are published in the journal Endangered Species Research.