I received a fair number of responses for this, considering how difficult it was, and the most frequent answer I got was Common Tern. Despite the long bill, I would argue this is not a Common Tern but an Arctic Tern. Common Tern should show dark secondaries and a dark contrasting (almost black if not black) ulnar bar. This bird has a fairly uniform upperwing with white secondaries.
Although the lighting is crap and there is a dark shadow over the underwing, I think the important underwing field marks can be made out. First is, as I pointed out, the narrow black tips to the primaries. I would expect much broader tips to Common Tern, giving a wedge shaped black band on the primaries. Though this is not always the case, it is true of most. The other important character is that all secondaries and primaries are translucent from underneath as opposed to the grayish and contrastingly dark secondaries of Common. The head also appears small and rounded, but because of the angle I am hesitant to use these characters.
Here is a slightly better photo of a more typical non-breeding Arctic Tern from a better angle. Note short bill, thin black primary tips, translucent remiges, rounded head, short neck...
Markothy Markus Aurelius "Mark" Dettling
Thanks for playing -