The neighbourhood soundtrack is punctuated by their chip-notes, as in ones and twos they dart from tree to tree, street to street.
And how many people notice?
Today I saw one attack a preening Robin. The Robin was completely befuddled. I wasn't aware that warblers have it in for Robins.
The aforementioned rump.
Update: There are yellow-rumps a-plenty in Illinois, too. Note that those birds have white throats, thus are "Myrtles." Most or all of the birds I saw here today were the yellow-throated "Audubon's" form. These two forms were formerly considered separate species, but some years ago were lumped. It is possible that some time soon they may be split again. Taxonomy is more vibrant than you might expect.