- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular breeding species and migrant; observed during the winter months in open-water areas, especially along the open-water stretches of the Mississippi River from central Minnesota south to the Iowa border. The Common Merganser was an uncommon species during the Minnesota Breeding Bird Atlas (MNBBA).
Distributed across the boreal forests of North America and Eurasia, the Common Merganser’s breeding range in North America extends from southeastern Alaska across Canada and as far south as the northwestern and west-central United States, the northern Great Lakes, and New England. Its distribution and relative abundance in southern Canada and the United States, as depicted by the federal Breeding Bird Survey (BBS), are shown in Figure 1.
A game species, the Common Merganser has been assigned a Moderately Low Continental Priority by the North American Waterfowl Management Plan and has been assigned a Continental Concern Score of 7/20 by Partners in Flight.
A short- to medium-distance migrant that winters across the central and southwestern United States, south to northern Mexico. Some populations are year-round residents.
A diver that feeds primarily on small fish but occasionally consumes aquatic invertebrates, small vertebrates, and plants.
Primarily a secondary-cavity nester but may nest in rock crevices, in holes under tree roots, along an eroded shoreline, or in nest boxes.
The Common Merganser is a breeding resident across Minnesota’s northern forest landscape. In the first comprehensive account of Minnesota’s avifauna, Hatch (1892), a physician in Minneapolis in the late 1800s, wrote that he would find young Common Mergansers “on the ponds and small grassy lakes” of “his country” in the early days. Presumably he was remembering birds he saw in the lakes and ponds surrounding Minneapolis when he first moved to the area in 1858.
Many years later, when Roberts (1932) wrote his two-volume treatise on Minnesota birds, he included this note from Hatch, as well as several other reports that mention the species’ presence and presumed breeding status in southern Minnesota. One account was from Dr. Hvoslef, an avid student of Minnesota’s bird life and a physician who lived and practiced in Lanesboro. In 1888, Dr. Hvoslef wrote that he “saw a female and I think 2 very small young close by.” Combined with 2 other accounts from Iowa and Heron Lake, the reports led Roberts to suspect that Common Mergansers once nested in limited numbers as far south as the Iowa state line.
At the time of his writing, however, there were no recent records from southern Minnesota. Instead, the species was considered a common summer resident in the northern forested regions of the state, particularly in the “triangle formed by the Rainy and Pigeon rivers on the north and Lake Superior on the south” (Roberts 1932).
Whether the Common Merganser ever nested south of its primary range in northern Minnesota is unclear. In their updated account of the species in 1975, Green and Janssen describe the species as a resident in the north-central and northeastern regions of the state. They noted the three 19th-century records mentioned by Roberts (1932) in Fillmore (1888), Hennepin (Hatch’s account in 1892), and Jackson (1887) Counties but remarked that there has never been further information to suggest that the species ever nested in the central and southern regions. Yet recent summer observations west of the species’ primary breeding range, in Clearwater and Otter Tail Counties, prompted them to encourage observers to look for the species in these areas. The species is strongly associated with deep, clear lakes and rivers, and thus the shallower and often turbid waters of southern Minnesota’s lakes and rivers seem ill suited for this diving bird. Furthermore, it would not be unusual for the female Common Merganser and young to be confused with the female Hooded Merganser, which is a regular breeding species in southern Minnesota. On the other hand, there are other historical accounts of a more southerly breeding distribution in Pennsylvania and, in the past 50 years, within Virginia (Pearce et al. 2015). Indeed, the species declined as a breeding species in these areas in response to hunting pressure and water-quality degradation. With more regulations and community efforts to improve water quality, Common Mergansers are now recolonizing some portions of their former range, where some of the largest gains have been seen in New York, Pennsylvania, and Vermont (Pearce et al. 2015).
In 1987, Janssen delineated 6 northern counties where breeding had been confirmed since 1970: Beltrami, Cook, Koochiching, Lake, Lake of the Woods, and St. Louis. By 1998, Hertzel and Janssen had added 2 additional counties: Cass and Itasca. Several years later, in 2006 and 2008, nesting was confirmed in Mille Lacs and Crow Wing Counties, respectively (Minnesota Ornithologists’ Union 2016).
The Minnesota Biological Survey reported 48 breeding season locations for the Common Merganser through 2014. All but 1 of the records were from 5 northern counties: Beltrami, Cook, Itasca, Lake, and St. Louis; 1 record was from southern Pine County (Minnesota Department of Natural Resources 2016).
During the MNBBA, participants reported 397 Common Merganser records from 6.2% (294/4,740) of the surveyed atlas blocks and from 5.8% (135/2,337) of the priority blocks. Breeding was confirmed in 88 (1.9%) of the surveyed blocks (Figures 2 and 3; Table 1). The birds were reported from 27 of Minnesota’s 87 counties and were confirmed breeding in 15 counties. In addition to the counties identified by Hertzel and Janssen in 1988, breeding evidence was confirmed in Aitkin, Hubbard, Itasca, Morrison, Sherburne, Stearns, and Wabasha.
The Landcover Suitability Model generated using MNBBA data clearly suggests the preponderance of highly suitable habitat in the Laurentian Mixed Forest Province (Figure 4) but also suggests scattered pockets of suitable habitat are present in the central and northern regions of the Eastern Broadleaf Forest Province, including the Twin Cities, and in the Tallgrass Aspen Parklands. Summer observations reported to the Minnesota Ornithologists’ Union in these regions certainly confirms the potential suitability of habitat in these localities (Minnesota Ornithologists’ Union 2016). Small pockets of suitable habitat also are predicted to occur further south in the state.
As the MNBBA did for the Common Goldeneye, it documented two centers of the Common Merganser’s breeding distribution in northern Minnesota. The first is located in the Arrowhead region, and the second in the north-central counties of Aitkin, southern Beltrami, Cass, Crow Wing, Itasca, and northern Mille Lacs. Records are sparse in the intervening industrialized Iron Range.
Perhaps more interesting are the scattered records farther south in east-central, southern, and western Minnesota. Most notable are the confirmed breeding records from Sherburne, Stearns, and Wabasha Counties. All of these records were examined carefully; a few records outside the core northern range were deleted due to coding errors. But the remaining records all were from qualified observers. The recent movement of birds from their core breeding range to areas farther west and south has been noted by observers submitting summer records to the Minnesota Ornithologists’ Union as well. From 1930 to 1979, there were summer records outside of the species core breeding range in only 6 years; from 2000 to 2014 there were summer records outside of the core breeding areas in 12 of the 15 years, including every year since 2006 (Minnesota Ornithologists’ Union 2016). Although some of these reports may be of late migrants, there is a clear trend of increasing summer reports in southern Minnesota. Even more significant is the number of confirmed breeding reports in central and southern counties. Consistent with the observations reported by Pearce and his colleagues (2015), the Common Merganser may be expanding or reoccupying areas of its former breeding range farther to the south in Minnesota. Roberts’s (1932) original speculation about the species’ former status in this region may indeed have been correct.
Further evidence of the species’ occurrence in more southern regions of the Great Lakes states was documented by atlas work conducted in Wisconsin and Michigan. Wisconsin’s first atlas (1995–2000) confirmed a breeding record as far south as Waushara County in the central region of the state, east of La Crosse (Cutright et al. 2006). They noted that although the Common Merganser is still an uncommon breeder in the state, atlas data indicated the species is “more plentiful during the summer in Wisconsin than previously thought.” During the first two years of the second atlas, breeding was confirmed also in Marquette County, which is located immediately south of Waushara County (eBird 2017). During Michigan’s second atlas (2002–2009), records documented the Common Merganser’s expansion in the Lower Peninsula. “Particularly notable is confirmed nesting on the Wayne/Monroe County line, a breeding location unknown in historic times” and located along the Lake Erie shoreline south of Detroit (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.