May 2, 2007—When the killer whales of Washington State's Puget Sound began vanishing, a biologist had to get an earful from the U.S. Navy to pick up clues to the mystery (Washington map).

Using supersensitive microphones, Ken Balcomb has been eavesdropping on the region's resident killer whales, also known as orcas. Unlike their transient brethren, these animals spend their entire lives in the sound.

But Balcomb's years of research unveiled a disturbing trend: Mature orcas were disappearing in the prime of their lives, and no one knew why.

Then, when his equipment was blasted by a cacophony from a passing Navy vessel, Balcomb suspected he'd found at least one piece of the puzzle.

Watch the Puget Sound orcas in action, and hear what the biologist and an expert at the Office of Naval Research have to say about sonar's impacts on marine mammals.