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Waterfowl population survey: Lake St. Clair

Like the eye of a storm, these black specks framed by encroaching ice on Lake St. Clair represent thousands of wintering waterfowl. Photo: CWS. Click to enlarge.

On a brisk December morning at London International Airport, a four-seater Cessna climbs into a pale sky etched with wisps of cloud and snow. The small plane heads west. Below, the cityscape gives way to a checkerboard of residential subdivisions, farms, harvested fields and forest fragments.

Waterfowl take advantage of waste grain on farm fields. Photo: CWS. Click to enlarge.

On board, Canadian Wildlife Service (CWS) staff review the morning’s flight route with the pilot. Gary McCullough and Norm North are preparing for an aerial survey of waterfowl along the wetlands and open iceholes of Lake St. Clair. The survey will document use by waterfowl populations of significant habitat areas of the lower Great Lakes. Some migrating birds linger along the shoreline well into winter, as long as ice conditions are suitable, feeding on waste grain in the fields that fan out from the shoreline.

The CWS first surveyed the Lake St. Clair area by air in 1968. This survey is part of the CWS contribution to the Eastern Habitat Joint Venture (EHJV), one of 16 such “joint ventures” established across the continent under the North American Waterfowl Management Plan. With a shared overall goal to conserve wetland and upland habitats for migratory birds, partners of the EHJV in Ontario are the federal government, the provincial government, Ducks Unlimited Canada, the Nature Conservancy of Canada and Wildlife Habitat Canada.

The Thames River. Photo: CWS. Click to enlarge.

At the mouth of the Thames River, the pilot banks to permit a better view of the frozen wetlands and begins to wing his way back and forth above flocks of birds. Norm watches for bird groupings and directs the route, while Gary notes species and numbers into a hand-held recorder. The survey continues over now-drained Bradley Marsh and moves on to the federally-protected St. Clair National Wildlife Area.

To the untrained eye, it is difficult to identify the birds. Most are distinctive only by comparison: white versus dark silhouettes against the ice, large and smaller shapes moving in the air. Gulls are easier to discern than ducks, as are the vivid, white Mute Swans, a large species that is abundant but not native to the area.

A Green-winged Teal, one of the waterfowl species wintering at Lake St. Clair. Photo: CWS. Click to enlarge.

Norm and Gary continue to survey the nearshore iceholes on the lake. Assemblies of Mallard and Black Ducks shift in complex patterns against the dark patches of water. With satisfaction, Gary notes a small grouping of Green-winged Teals, whose presence is atypical for this time of year.

Returning to the shoreline, the small plane meanders like a dragonfly over inland marshes, covering Big Point, Mitchell’s Bay, partially drained Ford Marsh, and Bear Creek, before making a broad loop over Walpole Island and Seaway Island, and finishing up along the international boundary. With the job completed, the pilot turns back to London, rising up and over a fast-moving squall sprinkling the landscape – and the birds – with a skiff of snow.

Gary and Norm will later determine that they observed 28,000 birds. A prior survey in late November had a total of 75,000 birds, including 18 different species. The autumn peak usually occurs near the end of October or early November. In autumn, totals can peak at about 150,000; spring numbers may total about 60,000.

For population surveys of this nature, the reality is that numbers of birds cannot be determined with complete accuracy. Small groups on the ground or water, or flushed by the aircraft, are counted directly. For larger gatherings, depending on the size of the group, surveyors estimate blocks of hundreds or thousands. In the case of large, mixed flocks, different species are estimated by percentage of the total flock.

More than just numbers, however, the key to long-term monitoring is in consistent application of methodology to achieve a reliable outcome. Over time, the resulting data reveal notable trends; the rise and fall of wild populations, the distribution of populations through a given range, and the response of the waterfowl to changing habitat conditions. These data are vital to setting EHJV conservation program objectives and to monitoring the subsequent impacts of conservation and management actions on wild populations.

Learn more

• Important Bird Area (IBA) site – Eastern Lake St. Clair *
• Ramsar site – Eastern Lake St. Clair *
• St. Clair National Wildlife Area – part of Environment Canada's Protected Areas Network *
• 1998 Update to the North American Waterfowl Management Plan, Expanding the Vision *
• Take the Waterfowl Quiz