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Île aux Hérons Migratory Bird Sanctuary (QC128)


Île aux Hérons Migratory Bird Sanctuary (QC128)

LaSalle, Québec

Latitude 45.419°N
Longitude 73.583°W
Altitude 25m
Area 12.41km²

Site Description

This site is located in the Rapides de Lachine section of the St. Lawrence River near Montréal, Québec. It includes: Île au Diable, Les Sept Soeurs, Île aux Chèvres, Île a Boquet, Île aux Hérons, and several unnamed islands. The site also encompasses the water around the islands, part of the Boquet peninsula, a dam, as well as Île Rock (Îles aux Sternes) which is just outside of the Migratory Bird Sanctuary boundaries.

Submerged vegetation around the islands consists of Northern Water Milfoil, American Water-plantain, Sago Pondweed, American Tape-grass, Water Stargrass, Tuberous Water-Lily, Large Toothwort and Common Skullcap. On the islands, Giant St. John's Wort, Pannicled Dogwood, and Staghorn Sumac are common herbaceous species. Basswood, White Elm, and Slippery Elm are the most common tree species.

The islands are of low relief, and the soils consist of a thin layer of till covered by alluvial material and some outcrops. The riverbed is comprised of rock and gravel. Rapides de Lachine is shallow, with the exception of two deep trenches (13.5 meters) located near Île aux Hérons. The river remains ice-free during most winters.

This Important Bird Area contains 13 provincially threatened or vulnerable plant species, including Spring Beauty, False Mermaid, Hackberry and American Bladdernut.


Île aux Hérons Migratory Bird Sanctuary contains nationally significant numbers of breeding Black-crowned Night Heron, Great Blue Heron and Great Egret. An average of 420 pairs of night-herons bred here in four years between 1993 and 1999. This is probably over 10% of the Canadian population. This site is also of national importance for Great Egret. In 1998 there were two pairs nesting on the site, which is 1% of the Canadian population.

The colony of Great Blue Herons that nests here was much larger in the 1990s than it was in the 1970s through 1980s. The average size of the colony over the last five years in which it was counted was 338 nests, with the largest count of 455 nests occurring in 1999. These numbers not only meet the general IBA congregatory threshold for wading birds at the national level, but are roughly equal to about 1% of the Canadian population of the herodias subspecies.

Moderate numbers of Common Terns and Ring-billed Gulls nest on Îles aux Sternes. The Commn Terns breed sucessfully, but may be affected by Ring-billed Gulls moving from Île de la Couvée. One to two pairs of Little Gulls tried to breed on Îles aux Sternes between 1982 and 1986, but had no success in fledging young. The breeding failure of the Little Gulls may be due to sudden variations in water levels.

During fall migration, several waterfowl species regularly occur at this site, including Common Goldeneye, American Black Duck, Mallard, Blue-winged Teal, and small numbers of Horned Grebe. In 1977, 40 Barrow's Goldeneyes were observed, which exceeds this species' 1% continental threshold. However a flock of this size is unusual here. Large wintering flocks of Red-breasted Mergansers also occur at this site (1,500 individuals in 1996). Mallards, American Widgeon, Gadwall and American Black Ducks breed here.

Conservation Issues

The river is used for water sports such as rafting, hydro-jetting, and kayaking which may disturb birds and accelerate erosion. People visiting the heronry and loud noises from the nearby built-up mainland can lead to fatalities of the young herons. This site also has problems with non-native flora out-competing native vegetation.

In 1937, this site was designated a Migratory Bird Sanctuary to protect Great Blue Heron colonies. It is also located in a Priority Intervention Zone (ZIP), is classified as a critical area for migratory birds, and has been designated as a potential Ecological Reserve.

Fish Habitat

A variety of freshwater and diadromous fish coexist in different habitats in the IBA. We found between 70 and 80 species (including historical records) in the area. Several species, such as the northern pike, the yellow perch and the common carp exploit the aquatic vegetation and the floodplains as a spawning ground, a nursery and a feeding ground. Others, such as walleye, freshwater specie with an important economic value in Canada prefer rather to spawn in fast flowing waters. A special feature of this area is the presence of salmonids introduced for sport fishing (brown trout, rainbow tout, and salmons). Salmons were introduced in the Great Lakes and some drift into the St. Lawrence River where they are sometimes caught by anglers. Brown trout and rainbow trout were also stocked in riffles (in the river) for sport fishing.

Several pressures threaten the availability of fish habitats: the creation of embankments, the artificialization of banks, the residential, commercial and industrial development as well as developing the road network, while agricultural, industrial and urban waste deteriorate the water quality. The Eastern sand darter, among others, is very vulnerable to pollution and it is now on the list of endangered species. Among the species listed at risk frequenting the site, we found the lake sturgeon, the channel darter, the bridle shiner, the American eel and some historical records mention the presence of copper redhorse, a fish endemic to Canada designated endangered. In addition, the presence of invasive species such as round goby, threatens the natural dynamics of ecosystems and the water level regulation of the Great Lakes creates risks for the availability of spawning habitats of certain species.

Major species present:
American eel
American shad
Bridle shiner
Brown trout
Channel darter
Common carp
Copper redhorse
Eastern sand darter
Lake sturgeon
Northern pike
Rainbow trout
Smallmouth bass
Yellow perch


The sector is characterized by clear, alkaline and slow flowing water. Theses conditions promote dense plant bed that can cover up to 50% of the water bodies. Submerged plant beds are dominated by wild celery and Eurasian water-milfoil, while emergent marshes are filled with bulrushes, arrowhead and cattails. Several duck species forage in these areas, including the scaup that is fond of wild celery.

Shoreline erosion, whether due to natural factors (wind, freezing and thawing cycles, absence of ice protecting the river banks in spring) or human actions (waves caused by ships), all threaten the riparian habitat. Water level fluctuations affect the ecology of plant and animal species that live there. A significant and prolonged decrease of bank immersion could affect flora by promoting more land species such as shrubs or even trees. In addition, the spread of invasive species exerts considerable pressures on the native flora of these habitats.

Major species present :
American bulrush
Broad-leafed arrowhead
Broad-leafed cattail
Eurasian water-milfoil – invasive species
Great bulrush
Narrow leaf cattail
Sessilefruit arrowhead
Wild celery

IBA Criteria Habitats Land Uses Potential or Ongoing Threats Conservation Status
Little Gull
Number Year Season
4 - 92006Summer
2 - 32005Summer
Herring Gull
Number Year Season
Chimney Swift
Number Year Season
27 - 802020Fall
40 - 1202020Summer
100 - 2002020Spring
40 - 2502019Summer
60 - 1502019Spring
25 - 832018Summer
100 - 9502018Spring
50 - 752017Spring
60 - 1252016Summer
53 - 1002015Summer
50 - 2,0002015Spring
25 - 2002013Spring
300 - 5002008Spring
Barrow's Goldeneye
Number Year Season
Black-crowned Night-Heron
Number Year Season