Male humpback whales lengthen their songs when exposed to low-frequency sonar, a finding that raises concern about the impact of man-made noise on marine life, US researchers say.
A US Navy research ship transmitted 10 42-second low-frequency sonar signals at six-minute intervals to 16 humpbacks during the breeding season, a time when males sing long, complex songs that are believed to be sexual displays.
The whales' songs, recorded by trailing underwater microphones, were 29 percent longer on average during the sonar transmissions.
The scientists, from Woods Hole Oceanographic Institution, Massachusetts, say that the mysterious life of whales makes this response hard to interpret.
The longer songs may be intended to compensate for the noise of the sonar, rather as people have to talk louder at noisy parties.
The findings spark concerns about how sonar, propellor noise and low-frequency radio transmissions may affect whales, dolpins and other sophisticated marine animals.
"Marine mammals that use sound to communicate, navigate and detect predators and prey may try to avoid loud sound sources up to tens of kilometers (miles) away," the scientists say.
In the case of humpback whales, "widespread alteration of their singing behavior might affect demographic parameters," they warn.
The research is published in Thursday's issue of the British scientific weekly, Nature - PARIS (AFP)
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