The Common Merganser is the largest of the three North American merganser species. It breeds across Canada in areas where trees are large enough to support suitable nesting cavities. The population size and trend for mergansers are not reliably known, as many aerial surveys do not distinguish between Common and Red-breasted Mergansers, whose breeding range overlap extensively. An important part of the species’ breeding range, the Boreal forest, is not covered very well by current surveys. However, the three merganser species can be reliably identified during helicopter-based plot surveys. In eastern Canada, Common Merganser numbers appear to have remained stable since the survey first began in the 1990s. Overall, this species is not heavily harvested by hunters. The harvest of Common Mergansers has been decreasing since the 1980s, with most of the harvest occurring in eastern Canada. This species has been identified as a priority for conservation and/or stewardship in one or more Bird Conservation Region Strategies in Canada.
The most important factor limiting the population size and breeding distribution of the Common Merganser is probably the availability of fish, but suitable nesting cavities can also play a role locally. In areas that were or are being logged, forestry practices may have reduced the availability of cavities suitable for nesting. Lake acidification and associated declines in fish populations can also reduce habitat quality (Pearce et al. 2015). Due to their trophic level, Common Mergansers are vulnerable to contaminants (e.g., mercury, lead), and may be useful bioindicator species for fish-bearing streams and lakes (Pearce et al. 2015).
Environment and Climate Change Canada and partners have developed Bird Conservation Region Strategies in each of Canada’s Bird Conservation Regions (BCRs). In these strategies, selected species are identified as priorities for one or more of the following reasons:
Select any of the sub-regions below to view the BCR strategy for additional details.
