[Tweeters] Bird song question

[Tom and Carol Stoner via Tweeters]

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
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