Common Merganser Mergus merganser Scientific name definitions

This large, cold-hardy, fish-eating sea duck nests worldwide near large lakes and rivers in northern forested habitats. In North America, it winters on large lakes, rivers, and reservoirs of the Pacific Northwest, Rocky Mountains, central United States, Great Lakes region and along the coasts as far north as Alaska. Also known as Goosander, a name sometimes restricted to Eurasian populations, the species has a variety of popular North American names that refer to mergansers in general, names such as sawbill, fish duck, and sheldrake. In flight, this duck has a flat, pointed profile. It generally nests in tree cavities (or nest boxes) but will nest on the ground or in crevices. Females breed in their second year, generally lay one clutch per year, and will lay their white eggs in the nests of other cavity-nesting ducks.

As a top predator in aquatic food chains, this species has served as an indicator of environmental health both for contaminants (pesticides, toxic metals) and lake acidification. Because this merganser was thought to threaten salmon and trout stocks, its diet has been intensively studied, and in some regions it has been the target of eradication programs. Although we lack a reliable estimate of its current population size, trend data suggest that the North American population is generally stable or increasing, with many northeastern US populations expanding south into former range.

The species has been studied extensively in breeding areas of Atlantic Canada (White 1957 White, H. C. (1957). Food and natural history of mergansers on salmon waters in the Maritime provinces of Canada. Bull. Fish. Res. Board Canada 116. Close , Erskine Erskine 1971b Erskine, A. J. (1971b). Growth, and annual cycles in weights, plumages and reproductive organs of Goosanders in eastern Canada. Ibis 113 (1):42-58. Close , Errington 1933 Errington, P. L. (1933). Food habits of southern Wisconsin raptors: Part 2. Hawks. Condor 35:19–29. Close ), British Columbia (Munro and Clemens 1937 Munro, J. A. and W. A. Clemens. (1937). The American Merganser in British Columbia and its relation to the fish population. Biol. Board Canada Bull. 55. Close , Wood Wood 1985a Wood, C. C. (1985a). Aggregative response of Common Mergansers (Mergus merganser): predicting flock size and abundance on Vancouver Island salmon streams. Canadian Journal of Fisheries and Aquatic Sciences 42:1259-1271. Close , Wood and Hand 1985 Wood, C. C. and C. M. Hand. (1985). Food searching behaviour of the Common Merganser (Mergus merganser). I: Functional responses to prey and predator density. Canadian Journal of Zoology 63:1260-1270. Close ), and in wintering habitats in the central United States (Salyer II and Lagler 1940 Salyer II, J. C. and K. F. Lagler. (1940). The food and habits of the American Merganser during winter in Michigan, considered in relation to fish management. Journal of Wildlife Management 4:186-219. Close , Huntington and Roberts 1959 Huntington, E. H. and A. A. Roberts. (1959). Food habits of the merganser in New Mexico. N.M. Dep. Game Fish. Bull. 9. Close , Anderson and Timken 1971 Anderson, B. W. and R. L. Timken. (1971). Age and sex characteristics of Common Mergansers. Journal of Wildlife Management 35:388-393. Close , Mccaw III et al. 1996 Mccaw III, J. H., P. J. Zwank and R. L. Steiner. (1996). Abundance, distribution, and behavior of common mergansers wintering on a reservoir in southern New Mexico. Journal of Field Ornithology 67:669-679. Close ). Diet of this species is well understood, as are its foraging and courtship behavior, growth, plumage molts, and relationships to pollution. Despite its broad distribution and importance as a bio-indicator of aquatic food-chain degradation, however, we know little about the nesting and reproductive biology of this duck, or its population size and dynamics.