- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular breeding species and migrant in Minnesota’s forests. The Wood Thrush was an uncommon species during Minnesota’s Breeding Bird Atlas (MNBBA).
Broadly distributed across the eastern United States from the eastern Great Plains to the Atlantic coast. In the Great Plains, it is usually found along the riparian corridors of major rivers. In Canada, it is found from southern Ontario east to southern Nova Scotia. Wood Thrushes reach their highest breeding densities in the central Appalachian Mountain region and in central Mississippi (Figure 1).
Assigned a Continental Concern Score of 14/20 and designated a Yellow Watch List species by Partners in Flight; designated a Species in Greatest Conservation Need by the Minnesota Department of Natural Resources.
A long-distance migrant that winters in Central America.
Omnivore that consumes a variety of insects, primarily soil invertebrates, and fruits while foraging on the ground and in the understory foliage.
Open-cup nest usually placed in a deciduous tree or shrub at a height of 2 to 5 m.
Roberts (1932) commented extensively on the distribution of the Wood Thrush in Minnesota. He described it as an abundant breeding species throughout the deciduous forest region, nesting as far north as the southern limit of the coniferous forests of northern Minnesota. It also nested in scattered woodland groves in western Minnesota. Roberts witnessed a gradual northward expansion of the species’ range as northern forests were harvested and replaced with younger aspen-birch stands more suitable for this deciduous forest–loving species. Exactly when the northward expansion began was unclear. “Several observers some years ago,” he wrote, “reported the Wood Thrush at localities well within the Canadian Zone, [such] as Leech Lake and the Crooked Lake region in northern Cass County, but as these records were made upon song-identification, they were not regarded as conclusive.” He was referring specifically to the similarity between the song of the more southerly distributed Wood Thrush and the more northerly distributed Hermit Thrush. Considered among the most eloquent of bird songs, both have an ethereal quality that has been lauded by naturalists for hundreds of years. To the untrained ear, however, they can sound remarkably similar. So it wasn’t until Roberts had credible reports from well-trusted colleagues that he accepted the evidence that Wood Thrushes were indeed expanding northward. Acceptable reports came from the Mille Lacs region (1926), and from Pine (1919) and Itasca Counties (1930).
Roberts also commented extensively about the distribution of Wood Thrushes in western Minnesota. Found along the Minnesota River west to Chippewa County, they occupied woodland groves throughout the southwest region, including in Jackson, Lac qui Parle, Lincoln, and Murray Counties. Despite extensive searches farther north, “the conclusion is that it is but a rare local wanderer north of the Minnesota River Valley.” Statewide, confirmed nesting records (nests with eggs) were available from just 5 counties: Goodhue, Fillmore, Hennepin, and Houston in southeastern Minnesota, and Itasca County in north-central Minnesota. An inferred nesting report (nest only) was reported from Wabasha County.
By 1939, Olga Lakela reported the species in Duluth, where it likely nested in a maple-basswood forest along the Skyline Parkway (Lakela 1939). But few additional summer records in northern counties were reported until the 1960s and 1970s, when scattered sightings came from Aitkin County, southern St. Louis County, and Cook County (Minnesota Ornithologists’ Union 2016).
In 1975, Green and Janssen reported Wood Thrushes were most abundant in southeastern Minnesota, from Hennepin County south to the Iowa border. North and west of this region reports were sparse despite the apparent availability of suitable habitat. Recent records from hardwood stands along the North Shore of Lake Superior were believed to represent an expansion in the knowledge of the thrush’s distribution rather than an actual expansion in its breeding range. In the extensively forested landscape that extended north and west of Lake Superior’s shoreline, the species had yet to be reported.
Janssen’s updated account in 1987 noted an increase in reports from southwestern Minnesota, suggesting the species might be expanding its range farther west along the Minnesota River valley. Nesting had even been recently documented farther south, in Jackson and Martin Counties. Yet, given Roberts’s earlier accounts of Wood Thrushes in this region, the species might simply have been reoccupying portions of its’ former range following a period of intensive agricultural development. Elsewhere, little change was observed in the species’ distribution. Since 1970, Janssen identified 11 counties where nesting had been confirmed: Anoka, Brown, Clearwater, Crow Wing, Hennepin, Houston, Jackson, Nicollet, Ramsey, St. Louis, and Washington. By 1998, Hertzel and Janssen added another 7 counties to the list: Becker, Beltrami, Dakota, Lac qui Parle, Polk, Rice and Winona.
By 2014, the Minnesota Biological Survey (MBS) had reported 422 breeding season locations for the Wood Thrush. Included were numerous records throughout the Laurentian Mixed Forest Province, from Clearwater and southern Beltrami Counties, east through Itasca and southern St. Louis, Lake, and Cook Counties. The survey had yet to complete its work in the far north-central counties. Farther south, Wood Thrushes were common also along the upper Minnesota River valley as far as Yellow Medicine County (Minnesota Department of Natural Resources 2016).
During the MNBBA, observers reported a total of 585 Wood Thrush records in 9.2% (434/4,738) of the surveyed atlas blocks and in 12.4% (290/2,337) of the priority blocks. Breeding evidence was confirmed in 14 blocks (Figures 2 and 3; Table 1). The species was reported in 64 of Minnesota’s 87 counties and was documented nesting in 11 counties (1 block straddled 2 counties, Dakota and Scott). Six counties were additions to Hertzel and Janssen’s 1998 list: Cass, Itasca, Kandiyohi, Lake, Scott (included because of the block that straddled both Dakota and Scott), and Wright. Contrary to earlier accounts, the largest number of observations was now reported from the northern Laurentian Mixed Forest Province. Overall, the species distribution during the MNBBA was very similar to to reported by the MBS.
The MNBBA predicted distribution map (Figure 4) predicted moderate breeding densities in scattered pockets throughout the southern and western regions of the Laurentian Mixed Forest Province. The species was predicted to be present in low breeding densities elsewhere throughout the province as well as in scattered regions of the Eastern Broadleaf Forest Province, from the southeastern corner of the state northwest to Becker, Mahnomen, and Otter Tail Counties. Further west, low densities are also predicted along the prairie-forest transition region in west-central Minnesota and along the portions of the Minnesota River valley.
Clearly, the past 100 years has witnessed a major shift in the Wood Thrush’s distribution in the state. The extensive conifer and mixed coniferous-deciduous forests that covered the northern forest landscape in the late 1800s and early 1900s were unsuitable for the hardwood-loving Wood Thrush. Minnesota’s southern mesic hardwood forests comprised of sugar maple, American elm, basswood, and red oak provided ideal habitat as the species extended the periphery of its breeding range north along the Mississippi River drainage. Then, as agriculture and residential development cleared much of the southern Big Woods, Wood Thrushes gradually moved northward as second-growth aspen-birch-fir stands replaced the large pineries of the north woods.
The northern expansion observed in Minnesota was also documented in several New England states (New Hampshire, Vermont, and, more recently, Maine) and in the Canadian provinces of Ontario and New Brunswick (Evans et al. 2011). The species’ history in Wisconsin was similar to that documented in Minnesota. Originally it was a common species in southern and central Wisconsin and scarce farther north. Yet, by 1991, Robbins (1991) reported that breeding densities in the northern counties were four times those in the south. Several years later, however, the first state atlas (1995-200) documented the species’ absence from large areas of northern Wisconsin (Cutright et al. 2006). Contrary to the changes observed in Minnesota and Wisconsin, little change in the distribution of Wood Thrushes in the past 100 years was noted in Michigan (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.