The increasing number of Great Black-Back Gulls (Larus marinus) in the North-eastern United States has led to concern about their impact on other species of seabirds. Great Black-Back Gulls are more aggressive predators than the more common Herring Gulls (Larus argentatus), and there is particular concern about their impact on Common Eider (Somateria mollissima) ducklings. Great Duck Island supports a mixed colony of Herring Gulls (1200 nests), Great Black-Back Gulls (55 nests) and Common Eiders (19 nests). In addition, the island serves as a nursery for Eider crèches from nearby Little Duck Island. Most of the research was focused on a single Common Eider nursery in the southern intertidal zone of Great Duck Island that adjoins a major gull colony.

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