I was lucky enough to blunder into a skulking Prothonotary Warbler at Fort Rosecrans National Cemetery today while birding with Frank Meyer; please excuse the horrible photos but PROWAR is a damn rare bird here in California, particularly in spring.
While superficially similar to Yellow Warbler in these photos (it's not a particularly bright male...first year bird?), the long, pointed bill and sharply contrasting blue-gray wings set it apart...unfortunately, I was unable to get a clear shot showing the white undertail coverts. Several of us were lucky enough to get some much better views, albeit briefly....it was a sneaky little bastard.
You can see the blue-gray wings through the veg a bit better in this one. Stoked.