On Saturday afternoon, I heard the song of a Black-capped
Chickadee twice, and the call of a Black-capped Chickadee once,
in my neighbor's yard.  There were no mockingbirds in the area,
nor any active birders.  This is only an interesting observation,
since I believe that chickadees in the zone of overlap between
Carolina and Black-capped are known to exchange vocalizations, so
heard-only birds may not be reliably identified.  I did not see
the bird(s).

Bill Ellis
Eldersburg, MD