¹Canadian Wildlife Service, National Wildlife Research Centre, 1125 Colonel By Drive, Ottawa, ON K1A 0H3
²Canadian Wildlife Service, 4905 Dufferin St., Downsview ON M3H 5T4
³Canadian Wildlife Service, 867 Lakeshore Rd., P.O. Box 5050, Burlington ON L7R 4A6
⁴University of Minnesota, Department of Fisheries and Wildlife, 1980 Folwell Ave., St. Paul MN 55108

*Corresponding author: Craig.Hebert@ec.gc.ca

Summary

   Censuses conducted over the last 25 years indicate that breeding populations of colonial-nesting birds on Lake Erie have changed. During the most recent census (1997-2001) twelve species were confirmed nesting on the lake. The most abundant species was the Ring-billed Gull with 68,000 nests lake-wide. Breeding populations of Ring-billed Gulls and Herring Gulls increased from Census 1 (1977-78) to Census 2 (1990-92), and then showed slight increases (Ring-billed Gulls) or decreases (Herring Gulls). Double-crested Cormorant nests increased from 57 during Census 1 to 1,956 during Census 2, to 9,257 nests during the most recent survey. This translated into an annual population increase of 23% from Census 1 to Census 3. Common Tern populations declined through time, exclusively as a result of decreases in the Canadian breeding population. Breeding populations of Black-crowned Night-Herons also declined through time. Statistical analysis of organochlorine levels in Herring Gull eggs suggested that the rate of temporal decline of most contaminants has been constant or has increased during the period 1974-2002. Stable isotope analysis of eggs revealed changes in the diet of Lake Erie Herring Gulls that likely reflected declines in the availability of fish prey.