Bird Ventriloquists

I love listening to birds. They sing constantly around here and I’m up pretty early in the morning, catching their concerts. I love to hear their songs—taking joy in listening to old friends’ familiar calls and puzzling over songs that I can’t yet identify. Bird songs—when you put attention to them—are amazingly varied and complex.

Most of the singing occurs in the morning, by males declaring their territory. Before they dive into the day’s work, they wake up with boisterous song. The louder, longer, and more complex his song, the better his chance at attracting females, as well as deterring his rivals.

Birds can tell how far away their challenger is by the timbre of the received call. As sound propagates through the woods, its acoustic properties are altered. For example, high frequencies are muffled more than low frequencies; so the farther away the caller, the softer the call. A bird can listen to what he hears and judge the range of his adversary. If it comes from what he thinks is a safe distance, it’s no problem. If it sounds close, however, he’d best consider flying toward the sound and facing the guy down.

Now here comes the fascinating part: Some birds are able to alter the timbre of their song in a way that makes it sound to a rival that he’s closer than he really is. It’s a way of fooling the adversary into defending a boundary that’s appears nearer than it really is (or backing off). The crafty singer can then lie back and goof off, having effectively expanded his territory—by voice alone.

I look upon these birds as ventriloquists. I have no idea if we have such gifted avian tricksters around here—it’s a subtlety that my ear is as yet too uneducated to catch. But I do believe that our resident birds sometimes “throw their voice,” in the way that a human ventriloquist does—making it sound to the listener as if it’s coming from a different place; maybe not farther or closer, but a separate location.

What I sometimes can distinguish is a voice-throwing sound, when a bird calls in the woods—particularly with a two- or three-part song. When I hear the first part, I can roughly guess where he is—in what direction and how far away. But then the second part of the call sometimes throws me off: it can sound as if it’s coming from a different part of the woods—even though I know it’s the call of the same bird. It is discombobulating to hear the source of the call seemingly and repeatedly jump from one area of the woods to another. He may sound first like he’s down by the creek, but then he’s up on the hill, then he’s back down by the creek, then...