Dawn Chorus

An unexplained electromagnetic phenomenon that occurs most often at sunrise or shortly after, that (with the proper radio equipment) resembles the sound of a massive flock of birds. It is thought to be casued by high energy electrons that get caught in the Van Allen belts of the Earth's magnetosphere and fall to the Earth's surface in the form of audible radio waves. Dawn choruses occur more frequently during magnetic storms.

This phenomenon also occurs during aurorae, when it is termed an Auroral Chorus[?].

.WAV format recordings of the dawn chorus (http://image.gsfc.nasa.gov/poetry/sounds/sounds)