MIGRATION AND DISPERSAL IN GREAT-LAKES RING-BILLED AND HERRING-GULLS

Band-recovery data for Ring-billed (Larus delawarensis) and Herring (L . argentatus) Gulls were analyzed to determine the origins of gulls br eeding within the Great Lakes region, the extent of lake and colony fi delity, and the winter and breeding season distributions of gulls of v arious age classes. Most Great Lakes Ring-billed Gulls wintered along the Gulf Coast, especially in Florida. Most Herring Gulls wintered alo ng Lakes Erie, Ontario, and Michigan, although first-winter birds were more widely distributed and were recovered at greater distances than older birds. Movement into or out of the Great Lakes region by gulls o f breeding age was minimal. However, movement among colonies and lakes was much more extensive; lakes and colonies do not define distinct po pulations. Gulls banded as chicks tended to return as adults to the la ke, but not necessarily to the colony, where they where banded. Gulls banded as breeding adults were more likely to return in subsequent bre eding seasons to the colony at which they had been banded than were ch icks recovered as breeding adults. Gulls are probably not as colony-te nacious as previously believed, and natal dispersal plays a significan t role in establishing or maintaining colonies. Management plans for G reat Lakes Ring-billed and Herring Gull colonies should consider the e ffects of inter-lake and inter-colony dispersal.