Great Black-backed Gulls (Larus marinus) are known to prey upon a wide range of bird species, particularly adults, young, and eggs of seabirds and waterfowl. Here, I provide the first account of Great Black-backed Gulls pursuing and attacking, in flight, a medium-sized wading bird, the Glossy Ibis (Plegadis falcinellus). I recorded two observations at Stratton Island, Maine, the northernmost breeding site for the Glossy Ibis in North America.