A COMPARISON OF ABUNDANCE OF COLONIAL MARSH BIRDS BETWEEN 1991 AND 2001 IN THE CANADIAN PORTIONS OF LAKES HURON, ST. CLAIR, ONTARIO AND ERIE

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Because of concerns about the status of populations of colonial marsh birds in the Great Lakes basin, surveys of Black Tern and Forster’s Tern were carried out in 1991 and 2001 in coastal areas of the Canadian portions of Lake Huron, Lake St. Clair, Lake Erie, Lake Ontario, St. Clair River, Detroit River and Niagara River. Both surveys utilized a combination of volunteer field assistance and a paid field crew. Eighty-nine volunteers participated in the 2001 survey. 

In total, 1647 Forster’s Terns were detected at 22 colonies in the 2001 survey, whereas 1176 were detected at 24 colonies during the 1991 survey. Both the 1991 and 2001 survey data showed that about 95% of Ontario’s known population of Forster’s Terns breed in the wetlands of Lake St. Clair.

 Overall, Black Tern numbers were considerably lower in Lakes St. Clair (-56%) and Erie (-78%) in 2001 than they were in 1991.Smaller declines were also recorded for Lake Huron (-18%) and Lake Ontario (-5%). In the 2001 survey, 717 Black Terns were observed at 40 colonies, while the 1991 survey estimated a total of 1168 birds distributed among 73 colonies. This yields an apparent overall decline of about 35% over the 11-year period.

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