Have you seen a Brown-headed Cowbird? They are considered an unwanted bird because the female birds will destroy eggs from other bird nests and put their own eggs in their place. They like open pastures but I’ve seen them in my own backyard as well as at the Nisqually estuary. The online literature says that they like to hang out with blackbirds, so seeing that Red-Winged blackbirds are so common in the Puget Sound area, I guess it should be no surprise that we see these as well. The males are easy to identify as they have a brown head and a glossy black (almost iridescent) plumage.
They like to eat millet and other grains off of the ground, and the only time I saw them in my backyard when I was providing a bird seed mix. When I fill my feeders with only sunflower seeds, they’re nowhere to be found. The blackbirds also don’t like the sunflower seeds as much, but the Chickadees, Nuthatches, Finches, Grosbeaks, and Goldfinches all love sunflower seeds!