>>For about the last month I have heard a single sharp whistle call note
with no new bird to account for it when I've tried to track it down. It happens
once and then usually it will be at least half a minute to a minute before I
hear it again and I'll hear it two to three or four times before it stops.
Earlier this week I heard the sound twice when our Anna's was doing its
display. Could this be the source?<<

We have 3 winter Anna's residents, and we, too, heard a strange, sharp
whistles like the above about a month ago. We were in the front yard, and
looked all around trying to figure out where it was coming from. The only bird in
evidence: An Anna's. And sure enough, when we heard it again, it seemed to
come from him, but he was stationery, not displaying. Had never heard it
before in all our years of watching them, have not heard it since.

Pat
Newcastle, WA