Military sonar can change the behavior of whales, causing the ocean giants to avoid their usual feeding spots, a U.S. study found.

Writing in the Proceedings of the Royal Society B, the researchers said some blue whales off the coast of California have been seen to change their behavior when exposed to the sort of underwater sounds used during U.S. military exercises.

Researchers exposed tagged blue whales to simulated sonar sounds significantly less intense than the military uses.

"Whales clearly respond in some conditions by modifying diving behavior and temporarily avoiding areas where sounds were produced," said lead author Jeremy Goldbogen of Cascadia Research, a non-profit research organization based in Washington state focusing on marine mammal studies.

The whales were tagged with non-invasive suction cups sensors, which recorded acoustic data and high-resolution movements as the animals were exposed to the controlled sounds.

The area of the ocean off the California coast, where blue whales often feed, is also the site of military training and testing exercises that involve loud mid-frequency sonar signals, the researchers said.

"These are the first direct measurements of individual responses for any baleen whale species to these kinds of mid-frequency sonar signals," Brandon Southall, a researcher at the University of California, Santa Cruz, said. "These findings help us understand risks to these animals from human sound and inform timely conservation and management decisions."