The Hidden Complexity of Birdsong

Birdsong, and even calls, sometimes exhibits complexity that we humans cannot hear. Birds use these complex vocalizations to communicate a wide range of information, from breeding status to warnings.

One of the amazing examples that I recently came upon was a video (see below) by Lang Elliot, a bird photographer and videographer. The video is about the Henslow's Sparrow (Ammodramus henslowii), a small and reclusive species of grassland sparrow. The song of the Henslow's Sparrow, to us, sounds simple and boring, a "tsidlick", as its song is often described. Roger Tory Peterson, the inventor of the field guide, called it one of the poorest vocal efforts of any bird. But to the sparrows, their song is certainly not simple. At 0:57, Elliot slowed down the song to show its hidden complexity, turning it from "tsidlick" to what I paraphrase to a "deet-dew-dewdew-deet-dew!" The song turns out to be a series of well-defined notes pushed together into a short period of time; one has to wonder if the sparrows can hear and discern each note of the song jumble better than we can. One also has to wonder if the ancestors of the Henslow's Sparrow's had a song that wasn't so jumbled, so that a human really could hear each individual note. Once again, we find a behavior shrouded in mystery...