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COSEWIC Assessment and Update Status Report on the Ross’s Gull in Canada

Habitat

Habitat Requirements

Ross’s Gulls are known to breed in a variety of habitats, the most common being marshy wetland and subarctic and boreal tundra (Blomqvist and Elander 1981). They also nest in High Arctic Tundra and gravel reefs (Macey 1981, Bechet et al. 2000). Nesting requirements include access to open water such as lakes, ponds, polynyas or open leads in the pack ice and frequently near Arctic Tern colonies (Macey 1981, Béchet et al. 2000).

Principal habitat in the bird’s Russian range is where melting snow on tundra underlain by permafrost creates a muddy boggy terrain interspersed with shallow pools dotted with sedge Carex and moss, and with small low islets partly within small trees Alnus and Salix (Cramp et al. 1983, Densley 1991). All sites are located near water, and many are close to Arctic Tern colonies and sometimes to nests of medium-sized shorebirds such as Spotted Redshank (Tringa erythropus) and Ruff (Philomachus pugnax). The site used in Churchill is evidently very similar to the lowland habitat in Kolyma, Russia; it consists of hummocks supporting grasses, lichens and dwarf willows, lower areas with grasses and sedges, small pools and some shallow lakes (Chartier and Cooke 1980, Macey 1981, Alvo et al. 1996).

On the Cheyne Islands, Nunavut, nests were placed on low-lying gravel islands, each about 400 m long and 1 m high, supporting freshwater ponds and vegetation such as mosses, a nesting habitat quite different from the low-lying tundra of the bird’s Siberian range or the Churchill site. The nest site on the unnamed island in Penny Strait was on a gravel reef/island, near a colony of Arctic Terns; one nest was located on the elevated ridge running the length of the reef (Mallory et al. 2006). The nest on Prince Charles Island was located on a small island in a lake, on an elevated hump covered with moss and dwarf willow, in the transition zone from the wet coastal plain to the drier interior of the island, an area consisting of a network of medium-sized lakes on a low plateau on top of raised beaches (Bechet et al. 2000).


Habitat Trends

There appears to be no evidence that nesting habitats have been lost or created which would impact nesting Ross’s Gulls. It is possible that climate change could affect the permafrost layer, thereby changing the overlying structure and composition of the tundra, and rising sea levels could impact the low-lying gravel islands. 


Habitat Protection/Ownership

The Churchill Special Conservation Area (35,823.1 ha), designated under the Manitoba Wildlife Act, was established to conserve and protect Ross’s Gull nesting habitat around Churchill. This area is no longer used by Ross’s Gulls. The current Churchill breeding location is more difficult to access, providing some protection for the bird. The northern breeding locations in Nunavut are also partially protected because of their remote and inaccessible locations.