Whenever you're in a natural system and you're making sound, you are putting yourself at risk. As you go up the evolutionary ladder, from insects to frogs to birds and on up into mammals, the higher intelligence recognizes that when you vocalize, you put yourself at risk. So mammals generally vocalize or make noise much more rarely than, let's say, insects or frogs. And when they do, and put themselves at risk, it has to be worth the risk, and have true meaning, such as signaling during a hunting party, calling in prey, some religious or spiritual ceremony, something like that.

If you're tired of getting additional information, you can just close your eyes, get some sleep. But earlids, covering of the ears, never evolved. Not once do we find it, even in the fossil records. Because while we let our eyes relax, our ears are still hearing. And that's why alarm clocks work and wake us up. We still gather information. Every animal is gathering information 24/7. So I like to think of acoustic ecologists as people who are trying to become better listeners, 24/7.

You can listen to a birdsong, and from the content of the birdsong, you will be able to determine whether or not the bird grew up in a noise-polluted environment or whether it grew up in a pristine, clean environment. Isn't that incredible?

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.

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.

How are we going to know what sounds are important before we've even heard those sounds? It's an absurd question. The only thing we can say is that we're going to base it on our past experience. In other words, modern listening doesn't inform us of anything new. It simply keeps us in the past.

When you listen to nature, it may still be difficult to live a life, but it's inspiring.