This morning at the Mokelumne River Fish Hatchery there was a probable Chimney Swift flying rather low over the river. It was observed from the big parking lot just inside the entrance kiosk off and on for about 15 minutes in the direct company of about 20 Violet-green Swallows (about 100 were along the river). The bird consistently appeared as large if not larger than the swallows. Vaux's always appear smaller than Violet-greens to me, and they often move together during migration here in the Central Valley. However, I observed no other swift. Chimney Swifts are rarely reported in N CA not only because of the extreme difficulty in separating them from Vaux's, but they're also truly very rare. I wouldn't consider a Chimney if not for it being the direct company of the swallows.
Passerine migration was only modestly good with about 25 Yellow Warblers being the highlight in addition to the swift and swallows. Diversity was surprisingly low given the date.
