IBA Cowichan estuary
Duncan, British Columbia
Site Summary
BC048 Latitude
48.730° N
123.564° W
0 - 50 m
38.20 km²
salt marshes/brackish marshes, tidal rivers/estuaries, mud or sand flats (saline), inlets/coastal features (marine)
Land Use:
Agriculture, Fisheries/aquaculture, Tourism/recreation
Potential or ongoing Threats:
Disturbance, Filling in of wetlands, Industrial pollution
IBA Criteria: Globally Significant: Congregatory Species, Nationally Significant: Waterfowl Concentrations, Colonial Waterbird/Seabird Concentrations
Conservation status:
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Site Description
The Cowichan Estuary IBA is located approximately 9 km southeast of Duncan, BC on Vancouver Island. The Cowichan Estuary has been used by the Cowichan Tribes for generations for harvesting clams, geoducks, crabs, waterfowl, cod roe, urchins and salmon. This IBA encompasses the entire Cowichan Bay area stretching east to the southwest edge of Saltspring Island and south past Hatch Point. The sheltered marine waters are dominated by logging and shipping activities. Upland of the estuary is a fertile, coastal lowland dominated by farmland, streams, rivers, seasonably flooded areas, marsh, grassland and some forest. The village of Cowichan Bay lies along the southern edge of this IBA. Both the Koksilah and Cowichan Rivers drain into the estuary, meandering across silty mud flats as their freshwater merges into saltwater. These waterways produce Chinook, Coho and Chum salmon, and Steelhead trout.
Significant Species - The Cowichan River Estuary was designated for globally significant concentrations of Trumpeter Swan, Mew Gull, Iceland (Thayer’s) Gull, and waterbirds. The Cowichan area has notable numbers of overwintering Trumpeter Swan. Since 2000, numbers of swans counted during the Cowichan Christmas Bird Count have ranged from over 400 to more than 2000 birds within the count circle. The swans arrive in late October and have mostly departed by early April. They feed on discarded vegetables or corn cobs, green forage between harvested corn, and seedlings of various winter cover crops, as well as native vegetation in the estuary. Regular winter swan counts in the Cowichan area have recorded an increasing overwintering (February) population, from 500-700 swans in the Cowichan valley area (which includes farm fields, lakes, and Somenos Marsh IBA). Individual point counts within the Cowichan Estuary IBA itself have reached a peak count of over 400 swans. In the past, the Cowichan area has had notable numbers of Iceland (Thayer's) Gull and Mew Gull. In recent years numbers have decreased.

Historically, Western Grebe wintered here in globally significant numbers, with high counts ranging from 1858-4093 birds between 1985 and 1991. However, the numbers have declined steeply since then and only one count (in 1995) surpassed the 1% global threshold. This significant decline has been noted throughout the Salish Sea (British Columbia and Washington); the reasons for the decline are not clear but may be related to a decrease in forage fish and a subsequent southerly shift in wintering areas.

Other Species of Conservation Interest - The IBA supports important numbers of two species determined to be Threatened or Special Concern by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC; wildlife species that have been assessed as at risk by COSEWIC may qualify for legal protection and recovery under Canada’s Species at Risk Act). Great Blue Heron (fannini subspecies) (Special Concern, COSEWIC) has a colony in the IBA (as many as 82 individuals). 1-2 Peregrine Falcon (Special Concern, COSEWIC) are regularly seen in the IBA and area in winter. In addition, Marbled Murrelet, considered Endangered by COSEWIC, have been recorded in the IBA. Western Purple Martin (subis/arboricola subspecies) (Special Concern, COSEWIC) continue to increase in numbers.

Despite a gradual decline in waterfowl hunting over the last number of years, waterbirds such as Northern Pintail, Barrow's Goldeneye, and Greater Scaup have all dropped in numbers. Numbers of shorebirds have also decreased, while Anna's Hummingbird and Osprey have increased. American White Pelicans have stopped over during spring migration for the last five years.

IBA Criteria
SpeciesT | A | I Links Date Season Number G C N
Great Blue Heron 2010 FA 38
Great Blue Heron 2010 - 2020 SP 35 - 100
Great Blue Heron 2010 - 2020 SU 35 - 92
Great Blue Heron 2020 WI 80
Iceland Gull (Thayer's) 2016 FA 80
Iceland Gull (Thayer's) 1985 - 2014 WI 86 - 530
Trumpeter Swan 2016 SP 278
Trumpeter Swan 2009 - 2010 WI 258 - 408
Note: species shown in bold indicate that the maximum number exceeds at least one of the IBA thresholds (sub-regional, regional or global). The site may still not qualify for that level of IBA if the maximum number reflects an exceptional or historical occurrence.
Conservation Issues
The Cowichan Estuary has been the focus of conservation efforts since the early 1980s when conservation agencies like Ducks Unlimited, the Nature Trust of BC and numerous others began a campaign to set aside and restore as much of the estuary landscape as possible. Land purchases, conservation covenants, tidal restoration projects, farm improvements to optimize forage, and innovative land negotiations with landowners, the logging industry, port authorities and government agencies have all been used to set aside and manage important habitats in the estuary . These conservation efforts are helping to address a significant threat to the birds that use the estuary, including loss of wetlands and other key habitats.

The Cowichan Estuary Management Plan, initiated by the BC Government in 1987, was the first estuary management plan in BC. However the plan does allow for future expansion of an existing bulk transport terminal by infilling mudflats to the south of the terminal. Whether this would be allowed in future by Fisheries & Oceans Canada remains to be seen.

Increased development in the Cowichan Valley has led to an increase in disturbance, from recreational use including off-leash dogs and photography, boating traffic and various land use activities. Pollution from agriculture, industry and urban developments pose a potential threat to the estuary’s birds.

Within the IBA, members of the Cowichan Naturalists have been conducting standardized bird monitoring: Christmas Bird Counts since 1986, and weekly winter Trumpeter Swan Counts since 2009. Volunteers have been collecting monthly counts for the British Columbia Coastal Waterbird Survey since 1999.

The Cowichan Estuary is within the boundary of the proposed Southern Strait of Georgia National Marine Conservation Area Reserve proposed by Parks Canada. The work includes detailed collaborative work with Indigenous communities with interests in the area. When the NMCA is designated there will be specific zones for protection, enforceable regulations, and a management plan to ensure the protection of the biodiversity of the area.

The IBA Program is an international conservation initiative coordinated by BirdLife International. The Canadian co-partners for the IBA Program are Birds Canada and Nature Canada.
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