In the same family as gulls and terns (Larids), jaegers make their living swooping in and stealing prey from less agile fliers. And the long tail? Just an ornament, rarely seen outside of the breeding season. An easy way to tell a Long-tailed from the other jaegers? Check those outermost primary feathers: 2 bright white feather shafts in Long-tailed, 4-6 in the other species.
Photo Credit: Lucas DeCicco/USFWS.