Pittock Reservoir is an impoundment on the south branch of the Thames River, created by the Pittock Dam. This artificial lake forms the northeast boundary of the City of Woodstock. The dam was completed in 1966 to control flooding of the south branch of the Thames river as it flows through Woodstock, and to hold water for summer low flow augmentation. The resulting reservoir is 10.3 kilometres long with a summer surface area of approximately 452 hectares. The reservoir is drawn down starting in August to create storage capacity for fall rains and spring runoff; this results in new mudflats being exposed almost daily. The Pittock Conservation Area consists of a narrow strip of land bordering either side of the reservoir. One third of the conservation area is agricultural and about half is in naturally regenerating forest or conifer plantations.
Pittock Reservoir is known for its large congregations of gulls that start to build in numbers from late August and continue through to early winter; they roost and feed on the mud flats that are exposed by the draw down of the reservoir that starts in August. The maximum count of Ring-billed Gull, the commonest species, was 86,000 birds on September 22, 1988. Although counts have not been done recently, it is suspected that gull numbers may be even higher now. Another high count of 56,000 was made on August 26, 1989; these numbers are globally significant. Another gull present in globally significant numbers is the Herring Gull. On November 6, 1988, a total of 18,000 birds was seen, which represents over 5% of the North American population of this holarctic species.
Many waterfowl species utilize this reservoir for staging in both spring and fall migration. The most abundant duck is Mallard, with a maximum count of 15,000 birds on November 19, 1994. Common Merganser has been present in significant numbers, with 3,500 being tallied on December 3, 1988, representing over 1% of the Canadian population.
Other waterfowl found in moderate numbers include American Black Duck (500 in April), Lesser Snow Goose (155 in October), Green-winged Teal (180 in October), Canvasback (65 in November), Black Scoter (18 in October), Bufflehead (350 in April), and Hooded Merganser (55 in November).
Shorebirds also use the mudflats in the fall, with some noteworthy numbers being 600 Killdeer in October and 8 Upland Sandpipers in August. Common Terns can also be seen here, mostly in August. At the east end of the reservoir, in a 50 ha cattail marsh, at least 6 pairs of Least Bitterns (nationally vulnerable) nest annually, along with Marsh Wrens, Common Moorhens, Soras and Virginia Rails.
Conservation responses/actions for key biodiversity
There are no significant threats to this site that would impact the use of the site as a roosting and loafing area by the gulls or ducks. The conservation area is concerned about the impact of gull feces on water quality in the reservoir and downstream in the Thames River, the resulting impact on the recreational use of the site (swimming, boating, fishing), and the impact of the resulting algae blooms on the fish and other wildlife; at present, however, they have no immediate plans to do anything about the gulls.
BirdLife International (2023) Important Bird Areas factsheet: Pittock Reservoir. Downloaded from
http://www.birdlife.org on 21/03/2023.