"There's nothing new about studying animal sounds; biologists have been doing that for centuries. After all, if you want to understand birds, you need to understand how they communicate.

But Bryan Pijanowski is now asking his colleagues to take a huge step back and, metaphorically speaking, listen not just to the trees, but to the forest.

"We're trying to understand how sounds can be used as measures of ecosystem health," says Pijanowski, who teaches in the department of forestry and natural resources at Purdue University."

Richard Harris reports for NPR's Weekend Edition March 2011. [2]