Counting nests for conservation

By Kim Teager

While exploring Lake Superior National Marine Conservation Area (NMCA) this past summer, you may have spotted and wondered why Parks Canada staff were wandering over rocky islands and outcrops among hordes of screaming gulls. Did you know that counting nests in waterbird colonies is a great way of monitoring the lake’s ecological sustainability?

The Great Lakes Region provides essential breeding habitat for at least 17 species of gulls, terns, cormorants, herons, egrets, and more recently, pelicans. What do all these species have in common? They nest in colonies and eat mainly fish, making them excellent indicators for the health of coastal ecosystems because they reflect what's going on within the lake, and are vulnerable to both natural and human-caused changes.

Colonial waterbird populations are impacted by habitat degradation, environmental contamination (e.g., pesticides, microplastics, oil spills), changing water levels, commercial and recreational human activity, competition for resources, and predation. As high-level predators of fish, waterbirds are especially sensitive to changes in prey fish populations and the biomagnification of chemical pollutants through the food chain.

Great Lakes waterbird populations have been surveyed by the Canadian Wildlife Service (CWS) approximately once every ten years since the 1970s as part of a binational effort with the United States Fish and Wildlife Service. A complete count of active nests (with fresh materials, eggs, and/or chicks present) at each colony site visited provides an estimate of the number of breeding pairs in a given year. In June of 2023, our Resource Conservation team joined the CWS crew in the field for the first time to assist with nest counts for local colonies as part of the fifth Great Lakes survey. We visited islands in Nipigon Bay, Black Bay, and all along the archipelago from Thunder Cape to Simpson Channel.

Almost 140 colony sites have been found within Lake Superior NMCA boundaries over time, representing 30% of all sites on the Canadian side of Lake Superior. Herring Gulls nest on most of these sites, forming colonies that range in size from one breeding pair to a couple hundred. While Ring-billed Gull colonies are less widely distributed, they can reach several thousand pairs! Double-crested Cormorant and American White Pelican numbers are relatively lower; and Great Blue Heron colonies have been found at fewer and fewer islands with each survey. Caspian Terns rarely breed on Lake Superior, but pairs have been recorded with nests and chicks a handful times.

Although this year's final survey results are not yet available, a comparison with previous surveys will illuminate changes in population status and trends over time. They may also provide an early warning sign of potential stressors in the environment, as well as insight into ecological implications for other local wildlife and humans. Let us know about your waterbird sightings among the islands by sharing them on iNaturalist and eBird, but please observe from the safety of your boat as nesting birds are highly sensitive to disturbance.