Two Black Swifts cruised low over my head this morning as I was touring one of our restoration sites near Skyline Trail west of Hacienda Blvd. They were in a mixed flock that included other swifts (White-throated and Vaux's), as well as Cliff and Violet-green swallows.
The Black Swift is an uncommon and irregular transient throughout southern California, typically seen with other swifts and swallows in late spring (esp. May) and fall. They are very localized nesters in our area, with Big Santa Anita Cyn. being one of the traditional sites. They nest on the misty, mossy rock walls behind waterfalls.