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Site description (2001 baseline)
The Boundary Bay - Roberts Bank - Sturgeon Bank site is a large and complex area in southwestern British Columbia near the city of Vancouver. It includes Boundary Bay and the estuarine Sturgeon and Roberts banks, both of which are coastal wetlands and waters north and south respectively of the south arm of the Fraser River (which is also part of the site). Habitats found here include mudflats, and intertidal marshes predominantly composed of sedge, cattails and bullrush, which are critical to the Fraser River estuary ecosystem. The breakdown of detritus from marsh plants provides about 90% of the estuarine energy. The site also includes Point Roberts (USA) which separates the banks from the shallow Boundary Bay, Mud Bay and Semiahmoo Bay, all of which are more saline than the banks. At low tides, large mudflats form in the bays and extensive eelgrass beds are exposed. Finally, the fertile farmlands of Richmond, Delta, and south Surrey are part of this IBA. This site provides critical habitat for fish, such as the five salmon species, Herring, Coastal Cut-throat Trout and bottom fish species.

Key biodiversity
Boundary Bay, Roberts Bank and Sturgeon Bank form one of the richest and most important ecosystems for migrant and wintering waterbirds in Canada. The most numerous species found here is the Western Sandpiper there are one-day estimates of at least 500,000 during spring migration. Numerous species, including the Western Sandpiper, move from one part of this site to another; this is why these three areas have been amalgamated into one IBA. It is thought that a substantial proportion of the global Western Sandpiper population stops on the delta in the spring.

Dunlin occur in impressive numbers; one-day counts in the spring represent about 10% of the ssp. pacifica population, and 8% of the North American population. Large numbers of Black-bellied Plovers (one-day counts of as much as 3% of the estimated North American population) are recorded. Both Dunlin and Black-bellied Plovers winter in significant numbers. In total, fifty species of shorebirds have been seen in the area.

During the fall and early winter, one-day counts of greater than 100,000 waterfowl are made regularly. Some of the most abundant species include: American Wigeon (2% of the global population), Northern Pintail (1% of the North American population), Mallard (often occurs in numbers >20,000) and Green-winged Teal. Although not as numerous, significant numbers of Trumpeter Swans also winter, with a minimum of 4% of the Pacific Coast population being recorded. About 47% (or 46,700 birds) of the Wrangel Island Snow Goose population uses the banks. In the fall, one-day totals of 10,000 to 15,000 are more typical. In the spring, thousands of Brant (mostly ssp. nigricans) pass through the area. Numbers peak in April, with recent numbers typically between 1,250 and 3,300, or 1 to 2% of the Black Brant population. In the winter, smaller numbers of a different population are found; in recent winters about 200 Western High Arctic, or Grey-bellied Geese have been noted.

During the late summer and early fall, the area is also very important for moulting grebes. Between 2000 and 3000 Western Grebes are regularly present in Boundary Bay, and a separate study reports over 2,000 on the banks at a similar time of year. Thus, probably about 4% of the global population of the species is found here at this time of the year. Western Grebes have been recorded in significant numbers during the spring, fall and winter periods. As many as 2,500 Red-necked Grebes (about 5% of the estimated North American population) have also been recorded here in early fall. Large numbers of Glaucous-winged Gulls are present in the winter with an average of 19,000 gulls (from 1992 to 1997) being recorded (about 3.8% of the North Pacific population).

At least two nationally vulnerable species breed here. Three heronries of the Great Blue Heron ssp. fannini occur adjacent to Boundary Bay (at Point Roberts, Nicomekl River and Serpentine River). These colonies represent 6% of the total fannini population. These herons, and others presumably from colonies further away, feed in Boundary Bay and the banks throughout the year. The Fraser River delta also supports one of the last Canadian nesting populations of the nationally vulnerable Barn Owl. An average of 15 birds that were recorded on the 1992 to 1997 Ladner Christmas Bird Counts represents 1.5% of Canada's estimated population.

The marshes of Roberts and Sturgeon Banks support breeding American Bitterns, Soras, Virginia Rails, waterfowl and Northern Harriers, and outside the breeding season, large numbers of feeding swallows, Bald Eagles, Northern Harriers, and Peregrine Falcons. The area also supports large numbers of Short-eared Owls, Red-tailed Hawks and Rough-legged Hawks in the winter.

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Recommended citation
BirdLife International (2025) Important Bird Area factsheet: Boundary Bay - Roberts Bank - Sturgeon Bank (Fraser River Estuary) (Canada). Downloaded from https://datazone.birdlife.org/site/factsheet/boundary-bay--roberts-bank--sturgeon-bank-(fraser-river-estuary)-iba-canada on 15/01/2025.