Herring gulls ("Larus argentatus") and great black-backed gulls ("Larus marinus") are the most common gull species sighted on the refuge. They frequent all divisions throughout the year, but are most abundant in the autumn and winter when they roost on the marsh and tidal flats, and occasionally steal food from diving ducks in tidal creeks. Ring-billed gulls ("Larus delawarensis") also are common throughout the refuge, particularly during non-breeding season. During autumn and winter migration, Bonaparte's gulls ("Larus philadelphia") feed and roost at the mouths of tidal creeks and rivers throughout the refuge, but they are most abundant on the Biddeford Pool, Upper Wells, and Lower Wells divisions.