The Great Black-backed Gull (Larus marinus) was once rare in Michigan but since the 1950s it has become a common migrant, reported more frequently in the winter than the summer (Chu 1994). It is most frequently observed in Lake Erie, but reports from the other Great Lakes and even some inland sites (French 1997) have increased. Great Black-backed Gulls have generally increased in North America since the early 1900s, characterized by several significant range expansions (Good 1998). In the Great Lakes, this species was uncommon before 1931, but overwintering populations on Lakes Huron and Ontario have increased since 1934. A possible explanation for the increase in potentially breeding Great Black-backed Gulls in 1998 is that the winter of 1997-1998 was the mildest on record in Michigan (National Climatic Data Center 1998). Most regions of the Great Lakes were never covered by ice. These conditions may have favored movement of paired adults in the upper Great Lakes where they became established and remained to attempt nesting.