Listening to a Continent Sing

Here's an eastern bluebird with fire in his belly this early morning. He sings from a utility wire directly overhead, chattering between songs, and with no immediate repetition of songs, their variety seemingly endless.

But pick out a distinctive song that you can recognize and you begin to hear the limits of his voice. At 0:21, the seventh song is relatively simple; its first note is a whistle that slides down the scale, followed by a brief rising and falling whistle, with a typical eastern bluebird warble on the end. Get the feeling for that song and you'll hear it again, at 0:38, 0:56, 1:45, 2:11, 2:49, 3:09, 3:28, for a total of eight times, with five to 13 or so examples of other songs intervening between the successive repetitions. In studying the sonagrams, I pick out another song, the first one in the selection, and find that one ten times (compare the first song with the eighth song at 0:24, for example).

How many different songs does he sing here? The two songs that I've studied occur an average of 9 times apiece (average of 8 and 10). With 87 total songs in the sample, I calculate that he uses about 10 different songs. His repertoire is far larger, I believe, and for now he's singing only a subset of all that he knows. In just a few minutes he'd probably introduce a whole new subset of different songs.

Background

Water spills over the dam at Buckhorn State Park, creating a general rumble in the background; American robin, song sparrow, another eastern bluebird, chipping sparrow.

Photo by John Van de Graaff