March 11, 1854 in Thoreau’s Journal:

On Tuesday, the 7th, I heard the first song-sparrow chirp, and saw it flit silently from alder to alder. This pleasant morning, after three days’ rain and mist, they generally burst forth into sprayey song from the low trees along the river.  The development of their song is gradual, but sure, like the expanding of a flower. This is the first song I have heard.