Mystery Bird

Jeff Lewis photographed this Mystery Bird on 30 Apr 2010 at Alligator River National Wildlife Refuge, North Carolina. What is it? Opinions are divided between immature female Pine Warbler and Bell's Vireo. Features favoring Pine Warbler include dark auricular area sharply contrasting with pale throat, pale area curving behind the dark auricular, faint supraloral streak, whitish split eye-ring. Features favoring Bell's Vireo are about the same, except perhaps for the auricular. The bill seems to be warbler-thin. But what about the vireo-like hook at the tip?