While the Red-billed Tropicbird was the "best" bird our groups found over the 2 days, I think Black-capped Petrel was the most emblematic seabird. Sadly it was our only Pterodroma (though eventually it'll probably count as two...).
These birds knifing over the intensely blue Gulf Stream were entirely different than the local rat gulls lazing over much grayer Lake Michigan.
We saw a few of the light-faced types, the speculation is that the birds breed at different times (as evidenced by the differences in wing moult) and eventually will be split.
A last view of a Wilson's to try to highlight the differences with the final species...
I'm not sure how much of a difference can be appreciated in still pics of Wilson's (above) and Band-rumped Storm Petrels (below). Certainly the toes don't protrude past the tail tip in the Band-rumped. I somewhat get the sense of a bigger head, though would have the see the birds again to see if this is real or just an artifact of the first pic. The guides made a big deal about a different flight style that I'm not sure that I would recognize yet if they weren't calling the bird out.