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Common Loon
Gavia immer
– Family
Authors: Mcintyre, Judith W., and Jack F. Barr
Revisors: Evers, David C., and James D. Paruk

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Adult Common Loon with chick
Figure 1. Distribution of the Common Loon in North America.

The Common Loon (Gavia immer), one of five loon species worldwide, is a highly visible resident in North American waters. Many non-governmental organizations are dedicated to conserving this species, in part due to its great public appeal. Common Loons are widely-recognized symbols of northern wilderness and indicators of aquatic health. Landscape-level alterations, habitat disturbance, fishing practices and pollution threaten this species, but both individual loons and the overall population appear resilient and able to tolerate many of these threats, often within the same generation.

This loon is a long-lived bird with delayed maturity and low fecundity. In parts of its range, the natural history, population dynamics, movements, and pollution exposure levels of this species are now well-characterized because of long-term, landscape-level capture and color-marking programs. Recent advances in high-resolution models to predict population sustainability, individual performance, habitat quality, and mercury toxicity provide refined quantitative tools to support science-based policy decisions. In the United States and Canada, the Common Loon is being formally used in national mercury monitoring programs as one way to measure the impacts of mercury emission regulations. Further efforts in marking, sampling for contaminant and genetic profiles, and satellite telemetry will enhance long-term landscape-level conservation.

The large breeding population of loons in Canada is relatively protected from shoreline development and recreational activities. However, concerns remain over other threats that could harm these robust populations as well as far smaller ones in the USA. Such threats include contamination of lakes by mercury and acid rain, by-catch from commercial fishing, direct take through subsistence hunting, marine oil spills, botulism outbreaks, and emaciation syndrome. The synergy of mercury and acid rain threats may severely impact breeding loon populations across large areas of wilderness habitat. Acute, catastrophic events, such as the annual loss of large numbers of fall migrant adults to botulism outbreaks on Lake Erie and Lake Ontario are problematic, especially when combined with air pollutants that could be having severe impacts on the core breeding population in Quebec and Ontario, home to over 150,000 territorial pairs, or 70% of the range wide population of this species.

In short, the Common Loon has become one of the best studied birds in North America. While many basic questions of its natural history are being answered, continued landscape-level threats press for further studies. All of which point toward the Common Loon as a high profile representative for conservation and regulatory purposes.