When I consider the types of noise I hear in a day I realize, they mostly come from machines, vehicles or people. These noises are frequently loud or repeated over and over. Some of them indicate something I need to take notice of: a phone ringing, a car horn. Others are just there, such as a fan you are running or traffic outside. After a while, I don’t notice them, yet they still occupy the space.

That's not what other birds sound like. It is not part of anything I have to do. It is ignored, no response, no task is intended. It also isn’t part of some system or service that I rely on in any way. It isn’t business, a deadline or a duty. I recognize what kind of bird it is when I hear it, even if I don’t what kind of bird it is.

Its not always the same with the sound of a bird. It could be short or long, high or low, and regular or irregular. It could loop or change easily. Often, an individual bird makes a sound all by itself. At other times I hear three or four at once. I don’t tend to give it much thought when I hear it, though I pretty much always notice that I don’t mind having it there.