- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular breeding resident and migrant in Minnesota. The Black‑throated Green Warbler was a common species during the Minnesota Breeding Bird Atlas (MNBBA).
Primarily found in northeastern and upper midwestern portions of the United States and Canada, especially from Labrador to northern Alberta and south in the Appalachian Mountains to Alabama. The highest densities are found in the Upper Peninsula of Michigan, Labrador, and Nova Scotia (Figure 1).
Assigned a Continental Concern Score of 9/20 by Partners in Flight.
Long-distance migrant, overwintering in the Caribbean, Central America, and northern South America.
Insects, gleaned from foliage, especially caterpillars on conifers.
Cup-nest usually in conifers; often low but at variable heights.
Historically, the Black-throated Green Warbler was described by Roberts (1932) in the northern coniferous forests from northern Isanti County and west to Itasca State Park. He also described the species as formerly “a summer resident in considerable numbers in the heavy deciduous forest (‘Big Woods’) of Wright County in 1875.” Occasional pairs were found in the early 1930s in the heavy forests south of the coniferous region and in limited numbers around Lake Minnetonka in Hennepin County. He reported nesting behavior from only two areas. These included two from Mille Lacs, both with “young first seen out of the nest” and “feeding young out of the nest.” The other was a nest with four eggs in Itasca State Park, where the young left the nest on July 13.
Green and Janssen (1975) outlined a similar breeding distribution of northeastern and north-central regions and added confirmed nesting from Cook and Lake Counties, plus inferred nesting from Hubbard County. Janssen (1987) provided a similar distribution but cited observations south to northern Anoka County at Cedar Creek and as far west as Tamarac National Wildlife Refuge in Becker County. He noted confirmed nesting in 5 counties since 1970, including Beltrami, Clearwater, Cook, Crow Wing, and Lake, plus he emphasized its distribution in the northwestern region of the state was unclear. By 1998, Hertzel and Janssen added the species to the list of confirmed nesting in Aitkin County since 1970.
The Minnesota Biological Survey (MBS) identified 881 breeding season locations of the Black-throated Green Warbler (Minnesota Department of Natural Resources 2016). The distribution of these locations emphasized the primary breeding distribution in the northeastern and north-central forests. However, the MBS included several breeding season detections from northwestern Minnesota, including Roseau County and eastern Marshall County, west to Mahnomen and Becker Counties, and southwest to Douglas and Todd Counties.
The MNBBA included 1,741 records and reinforced the breeding distributions identified by the MBS. Nearly all of the records were from the Laurentian Mixed Forest Province but included scattered observations from the Tallgrass Aspen Parklands and from the extreme northern portion of the Eastern Broadleaf Forest Province (Figure 2). Nesting was confirmed in 35 blocks (<1% of all blocks) and in only 4.4% (35/795) of the blocks where the species was observed (Figure 3; Table 1). Additional counties with confirmed nesting from the MNBBA and not previously included in Hertzel and Janssen (1998) included Carlton, Cass, Itasca, and St. Louis Counties. The MNBBA also identified probable nesting in Becker, Koochiching, Lake of the Woods, and Roseau Counties, plus possible nesting from Marshall County and in southeastern Pine County.
The probability map indicated the species’ wide distribution in the northeastern and north-central regions with especially high concentrations predicted in Cook and southeastern Lake Counties. Higher densities were also predicted in several patches further west and south including in portions of Beltrami, Carlton, Cass, Clearwater, Hubbard, Itasca, and Koochiching Counties (Figure 4).
Roberts’s (1932) reports of the Black-throated Green Warbler in the Big Woods Subsection in the late 1800s suggested the species’ range had contracted substantially with the opening of the forests for agriculture and urbanization. Cutright et al. (2006) in Wisconsin supported this observation and stated that the species was likely found throughout the state prior to the clearing of forests during the 1800s. However, Cutright et al. found confirmed nesting in several places in central and southern Wisconsin during their breeding bird atlas, especially where large tracts of mature forest can still be found. Chartier et al. (2013) reported that even though suitable habitat in the southeastern Lower Peninsula of Michigan is dispersed and fragmented, the Black-throated Green Warbler has rapidly expanded into the southern regions of the state. They reported a 16% increase of townships where the species was reported in the Lower Peninsula over the twenty-year period between the first and second Michigan breeding bird atlases in the early 1980s to the early 2000s.
In their review of the Black-throated Green Warbler in North America, Morse and Poole (2005) suggested the species may have expanded its range westward in recent years in Canada but state the farthest northwestern breeding detections in the United States occurred in northwestern Minnesota. Morse and Poole also report an unusual disjunct breeding population that was found in the Ozarks and a recent expansion into the Ouachita Mountains of northwestern and west-central Arkansas.
*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.