- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular breeding resident and migrant, accidental in winter. The Swainson’s Thrush was an uncommon species during the Minnesota Breeding Bird Atlas (MNBBA).
The Swainson’s Thrush is found primarily throughout Canada and the western United States, with southern limits in the northeastern and upper midwestern United States. The highest densities are found in western North America from Oregon to British Columbia (Figure 1).
Assigned a Continental Concern Score of 10/20 by Partners in Flight.
Long-distance migrant; overwinters in Mexico, Central America, and South America.
Omnivore; insects and fruit, primarily gathered near the ground.
Cup nest in the understory of a shrub, sapling, or tree.
Roberts (1932) reported that he had limited contact with the Swainson’s Thrush and generally referred to it as “a summer resident in the northern evergreen forests as far south as Pine County and as far west as Itasca Park and Kittson County.” He reported confirmed nesting in Cass, Cook, Itasca, and Kittson Counties; the latter was the first nest found in Minnesota in 1896. All reports were of nests containing eggs, except the Itasca County observation, which was noted as “young feeding out of the nest.” The nests in Cass and Kittson Counties included cowbird young. Roberts reported observations of the Swainson’s Thrush in east-central Minnesota in the 1870s by Trippe as “Rather rare. Does not breed.” However, a report from 1922 referred to the species as “rather common” in Cook County, while Roberts and his colleague, Kilgore, also found it “fairly commonly” in northern Itasca County.
More than forty years later, Green and Janssen (1975) described the breeding distribution of the Swainson’s Thrush as northeastern and north-central Minnesota, plus adjacent northwestern counties. They remarked that the species’ present status in the northwestern counties and as far south as Pine County was unknown. They added confirmed nesting in Crow Wing, Lake, and northern St. Louis Counties. A few years later, Janssen (1987) suggested a more restricted breeding distribution, where the species was confined to the northernmost counties from Clearwater to northern Itasca, most of St. Louis, and all of Lake and Cook Counties. He suggested a northwestern distribution limited to eastern Roseau County. Janssen (1987) and Hertzel and Janssen (1998) only included confirmed nesting in Clearwater and Cook Counties since 1970.
The Minnesota Biological Survey (MBS) included 362 breeding season locations and emphasized the dominant distribution of the Swainson’s Thrush in the eastern portion of St. Louis County and especially throughout Cook and Lake Counties. However, the MBS included observations from one location in Carlton County, five locations in northern Itasca County, two in southern Beltrami County, one in eastern Marshall County, and two in northern Roseau County.
The MNBBA included 859 records that further reinforced the species’ major distribution in Cook, Lake, and northeastern St. Louis Counties, but it also scattered probable and possible nesting throughout Itasca, Koochiching, Lake of the Woods, and Roseau Counties (Figure 2). The breeding distribution of the Swainson’s Thrush was broad but was so scattered that it only appeared in 7.6% of all surveyed blocks (361/4,734) (Figure 3; Table 1). The most southerly observations were from 5 blocks in north-central Minnesota, including southern Cass and Crow Wing Counties and southwestern Aitkin County. Nesting was also confirmed in Crow Wing and northern Cass Counties. Other than the seven confirmed nesting observations in Cook and Lake Counties, confirmed nesting records included one in central Itasca County and two in St. Louis County, The latter included a record in southern St. Louis County in Hermantown, just northwest of Duluth. Possible nesting observations were also recorded in Beltrami, Hubbard, Kittson, and Marshall Counties.
The predicted probability map emphasizes the highest densities of the Swainson’s Thrush from southwestern St. Louis County to extreme eastern Cook County (Figure 4). High densities are also predicted throughout Koochiching County.
Historically, the lack of confirmed nesting and the limited number of confirmed nests was largely due to the difficulty in finding nests of the Swainson’s Thrush (Mack and Yong 2000). This difficulty was also noted in Wisconsin’s breeding bird atlas from 1995 to 2000, where nesting was confirmed in only 10 quads (Cutright et al. 2006). Breeding observations from the MBS and the MNBBA illustrated the breeding distribution in Minnesota is larger than previously outlined by Janssen (1987); but neither source included observations from Pine County, where Roberts (1932) previously recorded the species. There still appeared to be scattered, though sparsely distributed, populations of the Swainson’s Thrush in the northwestern counties of Kittson, Marshall, and Roseau. The intensive MNBBA coverage by astute observers in the Brainerd area also revealed breeding populations in central Minnesota.
*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.