Female Boat-Tailed Grackle. I've included the link to the Cornell site for this bird, but a lot of the information seems outdated - for example, the range only shows it in Florida and a tiny bit of the East Coast. And yet, there are large numbers of them here in California. Plus the recorded sounds on the website are nothing like the strange whoops and other noises I've heard them making.
Another shot of the female up in a tree. The males are larger, glossy black all over and have an unusual tail that they hold in an inverted V shape when flying.