I think that’s one of the reasons why the opening of Raiders of the Lost Ark is so effective. We hear birds and other animals but they are unsettling rather than reassuring. When Indy’s scout reveals the Hovido statue a flock of birds streams out of it and their panic tells us that there’s something dangerous here in the jungle and Indy is probably headed in the wrong direction.

Thats it! Maybe I misremembered where I read it ;D

My crackpot theory about songbird vocalizations, which I’ve posted about before, is that our eons-long association between the presence or absence of songbird vocals and the presence or absence of predators is the reason that a songbird is just about the only “natural” sound which always evokes a positive/optimistic feeling in a film audience. If we hear no songbird vocals in a forest we are on notice that danger may lurk.

Gordon Hempton discusses similar ideas about bird sounds in “One Square Inch of Silence: One Man’s Quest to Preserve Quiet”. We are keyed into the sound of bird calls because where there are birds there is food/fruits/vegetabes. If we as primitive nomads wander to a forest and hear no birds: then that is a dead forest with no food for us!

Somewhat related to Randy’s coment: the feeling of relief to your ears when a loud AC unit turns off (that you had forgotten was on anyway) makes me wonder what other sounds are out there that are constantly and subtly bombarding us that we arent even thinking about.