Do bird songs/calls change with the season? maturity of the bird? hormone
levels?

I ask because for the last month I've heard unusual bird sounds. Song
sparrows in our dense hedge travel along softly singing to themselves. I
tracked down a skulky bird in a brushy area making an odd twittering call
that finally contained a couple "dee dee" notes before I saw the B-C
Chickadee. Any thoughts?

Carol Stoner
West Seattle