Butter Butt

There are two subspecies of Yellow-rumped Warblers.
This immature female is a Eastern 'Myrtle Warbler'. If she lived in the Western U.S. we'd be identifying her as an 'Audubon's Warbler' and she would most likely have a yellow throat and a 'plainer' face. Both types sport a bright yellow rump patch, which is where the common name of 'Butter Butt' originates.