We saw many Laughing Gulls while in Cuba. This photo is of two on a dock that had a long line of Laughing Gulls perched on the edge of a dock off to the left. These two looked like they were posing to show off a front and side view at the same time. Their black and white color contrasts with the turquoise of the ocean behind them.
Their common call is a loud, descending series of laughing notes lasting 3 seconds or more.
Answer: Yes, they laugh.