Black-legged Kittiwakes are gulls of the open ocean. To see them in New England, I recommend sea-watching with a decent spotting scope or birding by boat, especially during the colder months of the year. In summer, they gather in colonies to our north, where they build their nests on cliff faces.
Smaller than a Ring-billed and larger than a Bonaparte's, a Black-legged Kittiwake is about the same length as a Laughing Gull. Adults have an unmarked yellow bill, black wing-tips lacking white windows, and, of course, black legs.