I have over thirteen years of birding under my belt, and can usually identify most species in the United States (except for the fall warblers, gulls, and terns).
On a recent trip to Bombay Hook National Wildlife Refuge, I recorded this odd duck which I originally believed to be an Oldsquaw (Or Long Tailed Duck). But upon closer inspection, the bird's bill shape and size were not consistent with an Oldsquaw. I am stumped. I believe it could be a hybrid or albino species, but I am out of ideas.