¹18 Timmsdale Crescent, Fonthill, ON, L0S 1E5
²Canadian Wildlife Service, Ontario Region, 4905 Dufferin St. Downsview, Ontario M3H 5T4
³Canadian Wildlife Service, Canada Centre for Inland Waters, 867 Lakeshore Road, Burlington, Ontario L7R 4A6

Summary

         Personnel of Canadian and United States wildlife agencies completed three major surveys (1976-1980; 1989-1991; 1997-2000) to census colonially nesting waterbirds breeding on the North American Great Lakes. We here summarize and comment on the numerical and distributional patterns of the five species breeding on Lake Superior during these census periods: Double-crested Cormorants (Phalacrocorax auritus), Great Blue Herons (Ardea herodias), Ring-billed Gulls (Larus delawarensis), Herring Gulls (Larus argentatus) and Common Terns (Sterna hirundo). There were orders of magnitude differences among maximum numbers of nesting pairs in periods of their highest count (DCCO – 5,359 pairs in third census; GBHE – 1,016 pairs in second census; RBGU – 26,920 pairs in second census; HERG – 27,135 pairs in second census; COTE – 944 pairs in third census). Numbers of Great Blue Herons and Herring Gulls increased between the first and second census, then decreased by the third census. Common Terns and Double-crested Cormorants increased in each census period, while Ring-billed Gulls increased between the first two periods then remained stable in the third. Numbers of all species increased from the first to the third census but with wide variation in the average annual rate of increase (from +0.7% for herons to 30.3% for cormorants). We identify major differences in the census and timing techniques used within and among years. We suggest that while these techniques underestimated the size of the actual breeding populations, the data can be taken as a valid index of trends in numbers of breeding pairs. The second census of Lake Superior was the only one coordinated and completed in one year (1989). We strongly recommend that future censuses of each Great Lake be coordinated between the two national agencies using standardized techniques, and be conducted by lake rather than by species.