Lake St.Clair, which forms part of the Great Lake system, is located in extreme southwestern Ontario to the north of the cities of Windsor and Detroit. The St. Clair River provides an inflow from Lake Huron to the north, and the Detroit River provides an outflow to Lake Erie to the south. The Eastern Lake St. Clair IBA encompasses the eastern shore, marshlands and agricultural fields from the Sydenham river at Wallaceburg to the mouth of the Thames River and the open waters of Lake St. Clair, south of the St.Clair River delta under Canadian jurisdiction. The large delta and the shallow nature of the lake result in extensive areas of marshland that is characterized by both submerged and emergent vegetation. Walpole Island, which is located within the St. Clair delta, contains some of the most significant tall grass prairie /oak savannah communities remaining in Canada.
Lake St. Clair is recognized as being one of the most significant staging areas for waterfowl in southern Ontario. During studies completed in the 1970s and early 1980s, it was estimated that peak totals of waterfowl were over 60,000 during spring migration, and over 150,000 during fall migration. The site was estimated to support 1,137,000 Canvasback and Redhead waterfowl-days, and as many as 5,123,000 dabbling duck waterfowl-days. (A waterfowl-day equals the number of ducks multiplied by the number of days present). The agricultural fields along the east shoreline also support large numbers of Black-bellied Plovers and American Golden Plovers during spring migration. As many as 5,000 Black-bellied Plovers have been reported, which could represent as much as 3.5% of the estimated North American population.
In addition to being significant as a staging area, the Lake St. Clair marshes also support significant populations of breeding birds. One of the largest breeding concentrations of Black Terns in Ontario is present, along with over 3.5 % of the estimated North American Forsters Tern population. The largest known Canadian population of King Rails (nationally endangered) has been recorded, along with significant numbers of Least Bitterns (nationally vulnerable).
The prairie and oak savannah communities of Walpole Island also support threatened bird species, with the largest self-sustaining concentration of Northern Bobwhite (nationally endangered) being present. There are also historic nesting records of Henslows Sparrows (nationally endangered), along with numerous other potential breeding records for nationally threatened species such as Acadian Flycatcher, Cerulean Warbler, Prothonotary Warbler, and Yellow-breasted Chat.
BirdLife International (2019) Important Bird Areas factsheet: Eastern Lake St. Clair. Downloaded from http://www.birdlife.org on 19/10/2019.