Hooded Merganser

A regular breeding resident and migrant; occasionally observed during the winter at open-water locations, especially in the Twin Cities metropolitan region. The Hooded Merganser was a common species during the Minnesota Breeding Bird Atlas (MNBBA).

The Hooded Merganser is broadly distributed across the eastern half of the United States, with a second, disjunct population in the Pacific Northwest. Although localized breeding populations occur throughout the southeastern United States, the core of the species’ breeding range is in the Great Lakes states. Its distribution and relative abundance, as depicted by the federal Breeding Bird Survey (BBS), are shown in Figure 1.

A game species, the Hooded Merganser has been assigned a Moderately Low Continental Priority by the North American Waterfowl Management Plan. Partners in Flight assigned it a Continental Concern Score of 8/20.

A resident to medium-distance migrant that winters in the southern United States.

A diver that feeds primarily on aquatic insects, small fish, and crustaceans.

A secondary-cavity nester; will use artificial nest boxes. Females have a very high fidelity to the breeding site.

Roberts’s (1932) brief history of the Hooded Merganser’s status in Minnesota is nearly identical to that of every other waterfowl species found in the state: “formerly an abundant migrant and common summer resident throughout the state but now much less numerous and a rather infrequent summer resident.” Overhunting was certainly common in the late 1800s and early 1900s, and no doubt it was largely responsible for the species’ initial decline. The Hooded Merganser is a forest inhabitant dependent on mature trees for nesting cavities. Thus, the wide-scale conversion of forests to agricultural lands in the southern half of the state, coupled with logging of mature, old-growth stands in northern Minnesota, would have had a major impact on the species as well.

Roberts’s account of the species included numerous reports of adults and young broods from locations throughout the state, from the cold, rapid streams of the Arrowhead region to the large wetlands and shallow lakes of the prairie. However, at the time of his writing, only 2 confirmed nesting records (i.e. nests with eggs) were reported: one in Becker County (1886), and one in Kittson County (1899). A female with a brood of half-grown young was also reported in Lake County.

The population eventually rebounded, and by the latter half of the 20th century, the species was reported as a regular summer resident in all but the southwestern region of the state (Green and Janssen 1975; Janssen 1987). It was considered most abundant in the southeast and north-central counties, “very scarce” in the west-central region, and absent from the southwest (Green and Janssen 1975). Janssen’s (1987) breeding distribution map excluded only the southwestern counties, from Lac qui Parle County southeast to central Martin County. He identified 29 counties where nesting had been confirmed since 1970. By 1998, Hertzel and Janssen had confirmed nesting in an additional 13 counties. Apart from a breeding record in Lac qui Parle County, the species was still not confirmed nesting in the southwestern or south-central regions of the state, despite observations of birds in the region throughout the summer.

As of 2014, field staff with the Minnesota Biological Survey tallied 180 Hooded Merganser breeding season locations during their fieldwork. The majority of records were from the Arrowhead region of northeastern Minnesota, the north-central counties of Beltrami and Clearwater, and from southwestern and south-central Minnesota (Minnesota Department of Natural Resources 2016).

During the MNBBA, participants reported 1,180 Hooded Merganser records from 18.8% (898/4,764) of the surveyed atlas blocks and from 20.5% (478/2,337) of the priority blocks. Breeding was confirmed in 386 (8.1%) of the surveyed blocks (Figures 2 and 3; Table 1). The birds were observed in all but 3 of Minnesota’s 87 counties (Chisago, Mower, and Wilkin) and were confirmed breeding in 73 counties. Overall, they were distributed across the entire state but were least abundant in the Red River valley, in the peatlands of north-central Minnesota, and in the southeast region. Although records were sparsely distributed across southern Minnesota, breeding was confirmed in 24 of the 31 counties located south of the Minnesota River.

The landcover suitability map for the Hooded Merganser (Figure 4) illustrates the suitability of habitats throughout Minnesota. The only extensive region of unsuitable habitat is in north-central Minnesota in the Northern Minnesota and Ontario Peatlands Section. Outside of the forested regions of northern and central Minnesota, riparian habitats throughout western and southern Minnesota provide suitable habitat, as does the greater Twin Cities metropolitan region, where the deployment of artificial nest boxes likely improves nesting opportunities for the species.

The Hooded Merganser was the fifth most frequently reported waterfowl species in the state during the atlas, behind the Canada Goose, Mallard, Wood Duck, and Blue-winged Teal. Clearly this spectacular little duck is faring quite well in Minnesota and has found suitable wetlands and nesting cavities even in the small woodlots that are scattered throughout the agricultural landscape. The widespread placement of Wood Duck nest boxes in this region has likely benefited the species as well.

Historically, Hooded Mergansers likely occurred throughout North America’s eastern deciduous forest before it was cleared, as well as in the mountainous regions of the western states. Small breeding populations still occur in many of these areas but are usually small in number and localized in distribution. Although the species now occupies most of its former breeding range, populations tend to be more localized in distribution and smaller (Dugger et al. 2009). More recently, Ontario witnessed no overall change in the merganser’s distribution between its first (1982–1985) and second (2001–2005) atlases (Cadman et al. 2007). Michigan documented a significant increase in the number of townships reporting Hooded Mergansers during its second atlas (2002–2008), although the species’ distribution changed little other than along the most southern two tiers of counties. Quite rare in this region of the state during the first atlas (1982–1988), they were reported from all but 3 of the counties during the second atlas (Chartier et al. 2013).

*Note that the definition of confirmed nesting of a species is different for Breeding Bird Atlas projects, including the definition used by the Minnesota Breeding Bird Atlas, compared with a more restrictive definition used by the Minnesota Ornithologists’ Union. For details see the Data Methods Section.

Hooded Mergansers use a variety of forested wetlands, including the riparian shorelines of lakes, rivers, and streams in otherwise open habitats (Figure 5). The limiting factor is the availability of nesting cavities or nest boxes (Baldassarre 2014). In Minnesota’s northern forest region, they are most frequently found on relatively quiet lakes and streams (Danz et al. 2007). The forest cover type is less important than the availability of suitable nest cavities. In the agricultural region, they use large, shallow wetlands and lakes that are surrounded by woodlots with appropriate cavities or where nest boxes have been erected. The features of the cavity are less important than its proximity to water. Cavities may be located in dead or live trees, in broken-off limbs, or atop broken-off tree trunks (Dugger et al. 2009). Old cavities excavated by Pileated Woodpeckers also are commonly used (Baldassarre 2014).

Once fledged, the young broods forage in shallow wetlands such as beaver ponds, marshes, forested streams, and small lakes. The water depth averages between 25 and 67 cm. Rocks, logs, and shallow bars are used as loafing sites (Dugger et al. 2009). In Wisconsin, 75% of the broods used wide, shallow, fast-flowing rivers that supported an abundance of small fish and crayfish (Kitchen and Hunt 1969).

Because Hooded Mergansers tend to be rather secretive and are principally an inhabitant of forested wetlands, they are difficult to survey. Indeed, many surveys do not distinguish among the three merganser species (Hooded, Common, and Red-breasted), reporting instead on the combined number of all mergansers. This is true of the most important survey for North American waterfowl, the North American Waterfowl Breeding Population and Habitat Survey (Zimpfer et al. 2015), which has monitored waterfowl populations since 1955. In lieu of breeding survey data, biologists have used harvest statistics and survival rates to generate a total population estimate of 329,000 to 414,000 birds from 1999 to 2006 (Dugger et al. 2009). Biologists with the Sea Duck Joint Venture (2005) estimate the size of the population to be higher, at approximately 485,000 birds. In contrast, the 2012 update to the North American Waterfowl Management Plan (2012) estimated the continental population at approximately 1.1 million birds, noting the estimate was somewhat speculative and based on few data. The species is not well monitored by the federal Breeding Bird Survey (BBS) (Sauer et al. 2017). Although the BBS data show a steady increasing trend survey-wide since 1966, the results are compromised by the species’ low abundance.

In Minnesota, the annual waterfowl breeding population survey does distinguish Hooded Mergansers from the other two large mergansers, Common and Red-breasted. Since 1987, annual numbers have fluctuated from no birds sighted during the surveys to a high of 3,765 birds in 2011 (Cordts 2015); in general the numbers demonstrate a slow, increasing trend with large annual variability (Figure 6). Because the survey is not conducted statewide, this number is an index rather than a statewide population estimate.

BBS data from Minnesota show a stronger population increase than those survey-wide, but the results are still compromised by the species’ low abundance and dependence on small forested wetlands that are not adequately surveyed by roadside counts (Sauer et al. 2017).

Although the Hooded Merganser nests throughout the eastern United States, including the southeastern states of Louisiana, Mississippi, Alabama, and Georgia, the core of its distribution is in the Upper Midwest. Estimates of nesting densities in Minnesota averaged at least 40 pairs per 100 km² (Zicus 1990) compared to estimates ranging from 1.4 to 11.1 pairs per 100 km² in southeastern Canada (Dugger et al. 2009).

Most of the focus on waterfowl populations has been on those species that nest in the Prairie Pothole Region. Because Hooded Mergansers are a forest species, occurring largely east of the region, far less attention has been directed at their life history and, consequently, their conservation and management requirements. The North American Waterfowl Management Plan (2004) classifies the Hooded Merganser as having a Moderately Low Continental Priority. Partners in Flight (2017) assigned it a moderately low Continental Concern Score of 8/20.

The Sea Duck Joint Venture was established in 1999, under the umbrella of the North American Waterfowl Management Plan, in an effort to direct more research and conservation attention to 15 species of waterfowl collectively known as “sea ducks.” The Hooded Merganser is one of the Sea Duck Joint Venture’s targeted species. A top priority is to more accurately assess the population numbers and long-term trends of sea duck populations.

Although they are a harvested species, Hooded Mergansers are not an important game bird. The merganser’s dependence on small fish means that it is not particularly tasty (Bent 1925). Regardless, in 2015 approximately 79,000 birds were harvested in the United States and Canada (Raftovich et al. 2016); nearly 48% of the entire harvest occurred within the Mississippi Flyway. Minnesota comprised 19% of the flyway’s total (7,210 birds) and 9% of the continental harvest.

Although unregulated hunting and the loss of large trees with potential nesting cavities were probably responsible for the species’ decline in the late 1800s and early 1900s, the increasing age of forests, particularly in the northeastern United States, is likely contributing to its recent increase in numbers. Nevertheless, at the local level the availability of suitable nest cavities may impact population numbers. Their availability can also be impacted in some regions by competition with Common Goldeneyes and Wood Ducks, two other waterfowl species dependent on secondary cavities (Dugger et al. 2009). Contaminants pose another concern. Hooded Merganser eggs in Minnesota measured in the 1980s had detectable levels of DDT, PCBs, and mercury and thin eggshells (Zicus et al. 1988). Bans on the use of these chemicals have resulted in a reduction in contaminant levels and an increase in eggshell thickness (Rave et al. 2014).

Studies have predicted variable impacts of climate change on the Hooded Merganser. The “State of the Birds 2010 Report on Climate Change” considered the species to have a relatively low vulnerability to warming temperatures. More recently, an analysis conducted on nearly 600 North American birds by the National Audubon Society classified the species as “climate endangered” and predicted that the species may lose 65% of its current winter range by the year 2080 (Langham et al. 2015; National Audubon Society 2016).

Until more is understood about the life history and population status of this elegant little member of the merganser family, the best conservation approach is to focus on best management practices that protect riparian woodlands and forests and improve wetland quality. Minnesota’s voluntary site-level forest management guidelines are an excellent resource to help guide forest landowners, loggers, and resource managers in achieving this goal (Minnesota Forest Resources Council 2013).