- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular breeding resident and migrant in Minnesota, the Blackburnian Warbler was common during the Minnesota Breeding Bird Atlas (MNBBA).
The Blackburnian Warbler is primarily found in the northeastern and upper midwestern regions of the United States and the eastern and central provinces of Canada. It is also found south in the Appalachian Mountains as far as northern Georgia. The highest densities have been observed in northeastern Minnesota, northern Wisconsin, central Ontario, and northern New York (Figure 1).
Assigned a Continental Concern Score of 9/20 by Partners in Flight.
Long-distance migrant, winters in southern Central America and northwestern South America.
Arthropods gleaned from foliage, especially coniferous trees.
Cup-nest, primarily in coniferous trees of variable height and usually high in the canopy.
Described by Roberts (1932) as found in evergreen forests in areas as far south as northern Isanti County, as well as in northern Sherburne, west to northeastern Otter Tail, eastern Becker, and Polk Counties. He also reported confirmed nesting in Becker, Cass, Cook, Itasca, and Lake Counties, and in Itasca State Park and Mille Lacs. All of these areas either had eggs, young in the nest, or young out of the nest being fed by adults. Roberts described the population in the evergreen forests as “evenly distributed and generally common through the entire region.”
By 1975, Green and Janssen emphasized that the Blackburnian Warbler’s primary distribution was in the northeastern and north-central regions, essentially the Laurentian Mixed Forest Province. They expanded confirmed nesting to include Beltrami, Clearwater, Hubbard, Mille Lacs, Pine, and St. Louis Counties. The authors highlighted that this species was found sparingly in the eastern fringes of the northwestern part of the state and the northern portions of counties in the east-central regions and that none had been observed in the cedar and tamarack bogs of Isanti and Sherburne Counties since the 1930s. Several years later, Janssen (1987) and Hertzel and Janssen (1998) added the species to the list of confirmed nesting in a total of seven counties since 1970, including Aitkin, Crow Wing, Clearwater, Cook, Hubbard, Lake, and St. Louis Counties.
The Minnesota Biological Survey recorded 526 breeding season locations, most of which were in areas previously identified. However, they also identified the presence of the Blackburnian Warbler in north-central and eastern Roseau, northeastern Marshall, southeastern Mahnomen, northeastern Becker, northeastern Wadena, northern Mille Lacs, Kanabec, and eastern Chisago Counties, plus a stray observation in northeastern Douglas County (Minnesota Department of Natural Resources 2016).
The MNBBA reinforced the previously described breeding distribution with virtually all 1,622 records reported in a total of 786 blocks, aside from three, in the Laurentian Mixed Forest Province (Figure 2). The exceptions were nesting observations in northwestern Minnesota, including possible nesting in central Roseau County and probable nesting in northeastern Marshall County. As with many secretive nesting species, only 4.6% of block records reported confirmed nesting (Figure 3; Table 1). The MNBBA did not add any additional counties with confirmed nesting records; probable and possible breeding activity was greatly increased for poorly sampled counties in extreme northern Minnesota, such as Beltrami, Koochiching, and Lake of the Woods.
Current evidence suggests that the Blackburnian Warbler has experienced a northward contraction all along the southern, western, and northwestern fringes of its breeding range in Minnesota. Isolated populations appear to exist in some areas where patches of large coniferous trees are found but certainly not in an “even distribution,” as suggested by Roberts (1932). Patches with confirmed nesting still exist in many parts of central and southern Wisconsin, even as far south as Walworth County (Cutright et al. 2006). This may be due to the greater presence of hemlock in Wisconsin. The National Forest Bird (NFB) monitoring program identified the Blackburnian Warbler as equally prevalent in mature white pine and hemlock forest cover types; the latter was exclusively found in the Chequamegon-Nicolet National Forest in northern Wisconsin (Niemi et al. 2016, p. 153).
In his review of the Blackburnian Warbler in North America, Morse (2004) cited limited evidence for range expansion into western Canada, as well as changes in the Blackburnian Warbler’s distribution in New York State over the past 100 years. He also suggested that the changes in New York were a result of recent reforestation in the Appalachian Plateau.
The Blackburnian Warbler’s presence during the breeding season can be easily overlooked because its high-frequency, insect-like song is most often emitted from the tallest of coniferous trees, where observations are challenging. Given its more southerly presence in Wisconsin, this species warrants more attention in areas of Minnesota with tall coniferous pines or spruce by observers with good hearing and visual skills.
*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.