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Site description (2001 baseline)
This site is located two kilometres east of the city of Beauharnois, and 30 km west of Montréal, Québec. Barrage de Beauharnois is situated at the mouth of the Beauharnois Channel and borders Lac Saint-Louis (a widening of the St. Lawrence River). The hydroelectric dam, two locks and a Hydro Québec power station are present on the site. From Beauharnois Channel, the water passes through turbines and emerges into three channels before entering Lac Saint-Louis. Immediately below the dam, a road crosses two islets. These islands and the surrounding waters make up this Important Bird Area.

Key biodiversity
Thousands of Ring-billed Gulls colonize the islands below the dam from March to December. Throughout the 1990s, an average of 6,742 breeding pairs were present on the island, which is 1% of this species’ national population. During this time the lowest count was 5,449 pairs (1994) and the highest was 8,059 pairs (2000). The landowners have installed exclosures on parts of the islands to prevent the gulls from nesting, but the gulls have moved to another part of the site on the other side of the road.

This site is also an important wintering site for gulls. In total, 17 gull species have been seen here. During the winter, gull flocks may contain as many as 25,000 birds. In November and December, Herring Gull flocks and Ring-billed Gull flocks are as large as 15,000 birds. In winter, Great Black-backed Gull, Iceland Gull, and Glaucous Gull are common, and Bonaparte’s Gull is the most common small gull. The dead fish coming out of the turbines are a great food source for the gulls.

Hundreds of terns (mostly Black Tern and Common Tern) also frequent the site in spring and fall. Five percent of the national Black Tern population (500 birds in 1984) and close to one percent of the North American Common Tern population has been recorded here. Pomarine Jaeger, Parasitic Jaeger, Laughing Gull, Franklin’s Gull, Little Gull, Black-headed Gull, Ivory Gull, Sabine’s Gull, Mew Gull, Lesser Black-backed Gull, Thayer’s Gull, California Gull, Forster’s Tern, Arctic Tern and Caspian Tern are also seen here irregularly.

In addition to the gulls, large numbers of swallows use the site during fall migration. Up to 72,000 Tree Swallows (1976) and 500 Bank Swallows (1977) have been recorded.

During migration, small numbers of ducks and shorebirds use the site, and occasionally Barrow’s Goldeneye and Peregrine Falcon (nationally vulnerable) are seen.

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Recommended citation
BirdLife International (2024) Important Bird Area factsheet: Barrage de Beauharnois (Canada). Downloaded from https://datazone.birdlife.org/site/factsheet/barrage-de-beauharnois-iba-canada on 26/12/2024.