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Site description (2001 baseline)
Marais (marsh) de Gros-Cacouna is on the south shore of the St. Lawrence River, about 10 km east of Rivière-du-Loup, Québec. The site encompasses a 10 km stretch of shoreline, that includes mudflats that are up to 1 km wide, and a 2 km wide strip of open water. The site also includes Cacouna Rock, Gros-Cacouna Island and a small bay east of the island. Other habitat types include cultivated fields, dykes and the Cacouna Port.

Key biodiversity
An aquatic bird survey in 1988, recorded 115,000 waterbirds in spring and 45,000 in fall, both globally significant numbers. The difference between seasons is mainly because of the larger number of Greater Snow Geese in spring, and also because of the presence of hunters scaring birds in the fall. Up to 100,000 Greater Snow Geese can be present in spring, representing 15% of the North American population. The majority of possible waterfowl species have been seen here, but two species stand out. As many as 3,000 American Black Ducks (1% of the global population) were recorded in fall 1979, and 50 Barrow’s Goldeneyes (2% of the species’ eastern population) were recorded in spring 1993. Species that are typically present in numbers exceeding 1,000 individuals include Northern Pintail and American Green-winged Teal. Species present in numbers ranging from 100 to 600 individuals include Brant, Oldsquaw, Gadwall, Blue-winged Teal, American Wigeon, Red-breasted Merganser and all three scoter species.

This site is considered one of the three most important shorebird sites on the river’s south shore, between La Pocatière and Matane. An incredible 10,000 Black-bellied Plovers were seen here in 1977, which represents 7% of the present North American population. In 1978, 1,000 each of Semipalmated Plovers and Short-billed Dowitchers were seen, representing 2% and 1% of their global populations, respectively. The numbers of Short-billed Dowitchers represents a high percentage of the population stopping in the St-Lawrence flyway and breeding in the northeastern part of the continent (mainly in Québec).

In spring 1994, 120 Black-crowned Night-Herons were present, which is more than 1% of the Canadian population. The birds were local breeders and used the deciduous forest southwest of Gros-Cacouna Island for roosting.

In the marshy area east of Cacouna port, nine male Yellow Rails were recorded in 1993, making this the third most important breeding site in Québec. Also breeding within the site are several species with restricted numbers or ranges in Québec, such as Nelson’s Sharp-tailed Sparrow, Wilson’s Phalarope, Le Conte’s Sparrow and Marsh Wren. Five species at risk nationally have been reported during migration or summer: Harlequin Duck, Red-shouldered Hawk, Least Bittern, Peregrine Falcon and Short-eared Owl.

The cliffs on the northwest side of Gros-Cacouna Island support a small colony of Black Guillemots (16 birds in 1990). In addition, Herring Gulls (peak number 670 pairs in 1989), Great Black-backed Gulls (peak number 75 pairs in 1990), and Common Eider (peak number 349 pairs in 1990) nest on Cacouna Rock. The number of eiders has dropped significantly in the last decade; only 49 pairs were recorded in 1996.

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Recommended citation
BirdLife International (2024) Important Bird Area factsheet: Marais de Gros-Cacouna (Canada). Downloaded from https://datazone.birdlife.org/site/factsheet/marais-de-gros-cacouna-iba-canada on 19/12/2024.