Unless you have actually SEEN these Black-throated Gray Warblers,
I would posit that you are hearing Townsend's Warblers. I heard
one singing this afternoon down the block from my house.

--
Mike Patterson
Astoria, OR
celata at pacifier.com

Dusty Book of the Month: _The Hawks of North America_
http://www.surfbirds.com/blogs/mbalame/archives/004483.html