- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular breeding species and migrant; the Blue-winged Warbler was uncommon in abundance during the Minnesota Breeding Bird Atlas (MNBBA).
Formerly an inhabitant of the Ozark Mountains east through the open woodlands of Tennessee, Kentucky, northern Alabama, and northern Georgia. Blue-winged Warblers have been expanding northward and now can be found throughout southern New England, southern Ontario, and the southern portions of the Great Lakes states. The species is sparsely distributed throughout its breeding range; some of the highest breeding densities can be found in the Appalachian Mountains, the mid-Atlantic states, and in western Wisconsin and Michigan (Figure 1).
Assigned a Continental Concern Score of 13/20 by Partners in Flight.
A medium-distance migrant that winters in Central America and the Caribbean islands.
Insects and spiders secured by foliage gleaning and probing.
An open-cup nest placed on or near the ground at the base of a shrub or a tussock of herbaceous vegetation.
The Blue-winged Warbler is one of many southern species that has expanded its range north along the Mississippi River floodplain, especially during the 20th century. Roberts (1932) provided a brief history of the warbler’s first appearance in the state in May 1880, when he found a male at Minnehaha Falls in Hennepin County. A few years later, in May 1885, Dr. Hvoslef found the species near the town of Lanesboro in Fillmore County. In 1889 he found a family of 4 in the same area, and by 1891 he had documented the first nest. In the following years, reports were logged from another site in Fillmore County in 1916 (near the town of Preston), again in Hennepin County in 1919, in Goodhue County in 1923, and in Winona County in 1922. Detailing these accounts, Roberts summarized the species’ distribution in the early 1900s as restricted to “a narrow area along the southeastern border of the state.”
When Green and Janssen (1975) provided an updated account of the species’ status, Blue-winged Warblers had been reported as a summer resident as far north as Dakota and Washington Counties. Reports of migrants were available farther north in Anoka County and to the west in Kandiyohi, Nicollet, Sherburne, Stearns, and Wright Counties, suggesting the bird might be even more widely distributed during the breeding season. The authors speculated that most of the northern expansion occurred in the 1940s, although they note that the timing may have coincided with an increase in the number of active observers in the state. Coincident with the expansion was an increase in the number of reports of Brewster’s and Lawrence’s Warblers, both hybrids between the Blue-winged Warbler and Golden-winged Warbler. Most reports of hybrids were from Goodhue, Hennepin, and Winona Counties.
When Janssen provided another update in 1987, he identified 6 counties where nesting had been confirmed since 1970: Hennepin, Houston, Olmsted, Scott, Washington, and Winona. By 1998 nesting had been confirmed in Dakota and Fillmore Counties as well (Hertzel and Janssen 1998). Observations were now being reported farther west along the Minnesota River valley in Scott and Nicollet Counties, and as far north as Stearns and Otter Tail Counties.
Beginning in the late 1980s and early 1990s, as the Minnesota Biological Survey began field work in the southern half of the state, field biologists documented a total of 107 Blue-winged Warbler breeding season locations. Although most records were restricted to the southeastern corner of the state, scattered reports were documented as far north as Morrison County in east-central Minnesota, and as far west as Lincoln County in southwestern Minnesota. The species was well represented along the lower Minnesota River valley from Shakopee to Mankato (Minnesota Department of Natural Resources 2016).
Additional northern records were documented during the MNBBA when participants reported 213 Blue-winged Warbler detections in 2.7% (129/4,737) of the surveyed atlas blocks and in 3.8% (88/2,337) of the priority blocks. The most northerly reports came from southern Cass County and northern Mille Lacs County; the most westerly record was documented near the South Dakota border in Big Stone County. Breeding evidence was documented in only 11 of the surveyed blocks but included 3 records north of the Twin Cities, in Anoka, Sherburne, and southern Pine Counties (Figures 2 and 3; Table 1). The birds were detected in 33 of Minnesota’s 87 counties and were confirmed breeding in 10 counties (2 blocks with confirmed breeding straddled Dakota and Scott Counties and one block straddled Carver and Scott Counties). Six counties were new to the list published by Hertzel and Janssen (1998): Anoka, Carver, Pine, Rice, Sherburne, and Wright.
The Blue-winged Warbler’s gradual range expansion in Minnesota originally was confined largely to the Eastern Broadleaf Forest Province. As the province was settled by European immigrant farmers, the forests were cleared for farmland and timber, soon providing ample early successional habitat favored by the species. The expansion witnessed in Minnesota was simply a continuation of a much broader movement north that had begun in many eastern states in the late 1800s and early 1900s (Gill et al. 2001). In the Upper Midwest, the birds were first reported in Wisconsin in 1867 (Cutright et al. 2006) and in Michigan in 1879 (Brewer et al. 1991).
As reports of Blue-winged Warblers increased in Minnesota and the species continued to expand northward, contacts with the more northerly distributed Golden-winged Warbler increased. This resulted in hybridization between the two species and produced two phenotypically distinct and fertile hybrids noted earlier: Brewster’s Warbler and Lawrence’s Warbler. Indeed a Lawrence’s Warbler hybrid was reported as early as 1945 in the Twin Cities (Eastman 1958), and a Brewster’s Warbler hybrid in 1956 at Whitewater State Park (Theodore 1956).
In their excellent review of the changing distribution of the two species and their hybrids, Svingen and Hertzel (2015) examined how the two species have come into increasingly frequent contact over the years. Their exhaustive review of both published and unpublished records found a total of 125 hybrid records in Minnesota since 1945; 108 of the records were from the southern half of the state. The authors noted the increasing rate at which hybrids were being reported. Although the increasing number of reports may be due to several factors, such as more observers actively searching for the birds, it does not bode well for the future of the Golden-winged Warbler. Another study by Vallender and her colleagues demonstrated that the only genetically “pure” population in the Golden-winged Warbler’s entire breeding range is in southern Manitoba, at the very northwestern edge of its range. Of the 96 Golden-winged Warblers sampled in Minnesota, 1 had genetic material acquired by hybridization with Blue-winged Warblers (Vallender et al. 2009). Although the rate of genetic introgression in the state was small, as the Blue-winged Warbler continues to move northward, this will undoubtedly pose an increasing threat to Minnesota’s Golden-winged Warbler population.
Indeed, prior to the initiation of the MNBBA, Blue-winged Warblers had already been reported during the summer months as far north as Becker, Cass, Clearwater, Hubbard, Lake, Mille Lacs, Morrison, and Todd Counties, all within the Golden-winged Warbler’s breeding range. Scattered summer reports also have been logged in western Minnesota, including in Jackson, Kandiyohi, Lincoln, and Otter Tail Counties (Beneke 1993; Bergman 1977; Millard 1984; Minnesota Ornithologists’ Union 2016).
*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.