The term “sound pollution” is well known, generally in the context of how it affects people’s quality of life.  We don’t generally think about sound as an environmental indicator.  Here is an interesting excerpt taken from http://www.danchan.com/weblog/andreapolli . Andrea Polli is Director of the MFA Program in Integrated Media Arts at Hunter College and her blog is called Ecomedia How the Natural World is Transforming the Nature of Media. I should have more posted about her work soon.

sound density is an important indicator of the health of a natural environment…

animal species populate the sound spectrum of an environment in much the same way they populate its geography. When in an environment, animals thrive when they can position themselves in different bands of the sonic spectrum than other animals. When a particular frequency band is open, this provides an opportunity for an animal to come into an environment without sonic competition. Animals have difficulty surviving in areas where their particular frequency band is already occupied.