Schumann's "Prophet Bird," from Waldszenen, is clearly birdsong. But it isn't just pretty and cheerful birdsong. It has an edge to it. The swooping birdsong calls emphasize a dissonant note at the start of each, then the dissonance resolves in a sudden upward rush of notes almost too quick to catch. Then there is a silence: from dissonance to brief resolution to nothingness. It's haunting music. Unsettling.
The end is a non-ending, just a restatement of the first couple of measures. Maybe the bird abruptly flies away. Maybe the end is in the future.
It's half hope, and half warning. As all the real prophecies are. Good Advent music.
Here is Myra Hess, playing with great genius.