The most sensitive frequencies are at the resonant frequencies of the auditory canal. In other words, the ear has shaped itself to naturally amplify certain bandwidth. And that corresponds to sounds in that bandwidth that were most important to our evolving ancestors to hear, in order to survive. And it doesn't match the human voice. It matches birdsong.

When we listen, it's not linear, it's 360, and it's in a time-space continuum, so you don't have to create a list of priorities, because it's all important. You can deal with everything at any given time. Not only that, but it happens very simply, without effort.

I used to hate the urban environment and the urban din. But I realize now that it's really not that much different than living next to a waterfall for wildlife. Most wildlife - unless they're specifically adapted - avoid being around a waterfall or whitewater streams and rivers because it jams their sense of surveillance. They are more vulnerable, and their message loses intelligibility. Now, the ouzel is able to overcome that in various ways. Back to the urban environment, we're talking and delivering messages as if we weren't next to a waterfall, and that's a problem.

If you're going to listen, you have to be willing to be changed by what you've heard. My life has gone through so many changes. I'm sixty-two years old right now, and I'm as busy changing now as I was when I was a teenager, or in my twenties. Every day is different. Every day brings new information.

Healthy areas that are richest in information are those areas in the wild where we can get all the information that's available to us within our human hearing range. The most valuable information throughout human evolution has been faint sounds. We tend to think in our modern world that if it's loud, if it grabs our attention, it's important. We get a lot of that in advertising. But in nature, it's the faintest sound that's important; it has determined, in the past of our ancestors, perhaps, if they will live or die. Faint sounds are the earliest clues of newly arriving information.

Not only does the modern person often think that sight is more important than sound - there's no objective evidence to indicate that. Many people, even audiologists who study the science of human speech and hearing, have assumed for a long time that the human ear evolved to hear the human voice, rather than the voice changing to fit the human ear. And the human ear is actually not a perfect match if we map its sensitivity to the different frequencies in the human range of hearing; it's an unequal curve, it's kind of a wavy line.

The birds are already evolving, changing the way that they sing as a result of noise pollution. And we have yet to do that. We're still not communicating. We're not changing our words. We are not testing, not providing this new lexicon for noise-polluted areas.