We're seeing a lot of Ruby-crowned Kinglets migrating through here right now. They're a cute small bird, more hyper than a warbler, and give a little, high-pitched call. Note the yellow-greenish color on the edges of the wing feathers. We see them flitting along the woodland edges here.
They really do have a ruby crown, but they keep it mostly hidden. When alarmed they can raise their head feathers and show the ruby.
Look for them in your yard, they're a treat and will take your mind off the fact few birds are coming to your feeders now, (more on the on Friday).