I accidentally photographed this bird from Port Deposit, MD on March 19th, 2011. The target of my photo was the Bonaparte's Gull in the upper right part of the first picture below. But on the lower left, out of focus, is a bird with a nearly-complete dark hood and a different shape than the Bonaparte's. Is this in fact the Black-headed Gull recently reported from Port Deposit and Lapidum (directly across the river in Harford County)?

This Black-headed Gull in non-breeding plumage was associating with a group of Ring-billed Gulls in the parking lot of the Hunt Valley, MD Best Buy on December 17th, 2011.