Great Black-backed Gull

Gulls and Double-crested Cormorants were the dominant birds along the periphery of Spectacle Island. The most numerous were Ring-billed and Herring, but there were also several Great Black-backed Gulls like the ones in the images above. A new life bird for me, though I have to admit to still being a little unsure of its identity. But everything seems to fit.
I discovered, while researching this species, that they are the world's largest gull and, though not overwhelmingly so, they definitely were big. Size, along with a much darker back, made them easy to pick out from the Herring Gulls, even the ones that still retained relatively clear, white heads from the breeding season.