- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular breeding resident and migrant throughout all but the very northern regions of the state. Regular in winter but not common; birds have been observed every winter since 1972, and some years before, dating back to 1922. Most winter birds are seen at feeders. The Brown Thrasher was a common species during the Minnesota Breeding Bird Atlas (MNBBA).
Widely distributed across eastern North America, from southern Alberta east to southern Quebec and New Brunswick, and from the U.S. Great Plains states east to the Atlantic coast. The core of the species’ breeding range is south of Minnesota, in the central Great Plains and the southeastern United States (Figure 1).
Assigned a Continental Concern Score of 10/20 by Partners in Flight; designated a Species in Greatest Conservation Need by the Minnesota Department of Natural Resources.
A short-distance to partial migrant that winters in the southeastern United States.
A ground forager whose diet consists primarily of arthropods but also includes berries, nuts, and waste grains. Occasionally gleans insects from foliage.
Open-cup nest usually placed within vines, shrubs, or small trees usually less than 3 meters above the ground.
In the early 1900s, Roberts (1932) remarked that although the Brown Thrasher was a common summer resident throughout the state, it was, like the Catbird, more abundant in southern regions of the state than in the north:
In thickly forested regions it seeks the more open places and clearings, avoiding the heavy timber. Every patch of woodland out on the prairies has its pair or more of Thrashers.
Nesting was confirmed (nests with eggs or young) from Rock and Lac qui Parle Counties in southwestern Minnesota, from Hennepin County in central Minnesota, from Polk and Marshall Counties in the northwest, and from Cass Lake in north-central Minnesota. Inferred breeding evidence (i.e., adults feeding young and/or a nest without eggs) was documented in Goodhue County, Itasca County, and Itasca State Park.
Many years later, Green and Janssen (1975) noted that thrashers were largely absent from the extensively forested landscapes of northern Minnesota. When present, they were found in forest openings created by timber management activities but appeared to be absent from natural forest openings. A few years later, however, Niemi (1978) documented that Brown Thrashers were common on the Little Sioux burn two to four years following the May 1971 fire that burned nearly 15,000 acres.
Janssen (1987) delineated 34 counties where nesting had been confirmed since 1970; records occurred in all regions of the state. A few years later, Hertzel and Janssen (1998) added another 7 counties to the list.
Field biologists with the Minnesota Biological Survey have documented 416 Brown Thrasher breeding season locations (Minnesota Department of Natural Resources 2016). Although they were found statewide, the birds were least common in the Laurentian Mixed Forest Province, and most common in the southern half of the Prairie Parkland Province.
During the MNBBA, participants reported 2,091 thrasher records in 29.5% (1,402/4,757) of the surveyed atlas blocks and in 42.5% (993/2,337) of the priority blocks. Breeding evidence was documented in 166 of the surveyed blocks (Figures 2 and 3; Table 1). The species was observed in all 87 Minnesota counties and was confirmed nesting in 62 counties (1 block straddled 2 counties: Marshall and Pennington); 34 counties were additions to the list published by Hertzel and Janssen (1998). The Brown Thrasher was most common in the southern two-thirds of the state, from Lake Mille Lacs southward, and was least abundant in the Laurentian Mixed Forest Province.
Atlas data were used to generate a model to predict the breeding distribution of Brown Thrashers statewide (Figure 4). The lowest probability is predicted in the far northeastern and north-central counties of the Laurentian Mixed Forest Province, especially in Cook and Lake Counties. Elsewhere in the province they can be found in the deciduous woodlands farther south and west and in developed areas, such as the Iron Range. They are predicted to be of moderate density elsewhere throughout the state with the exception of the southeastern Blufflands Subsection, where they are uncommon.
Over the past 100 years, the Brown Thrasher’s distribution appears relatively unchanged. It is likely more abundant in counties on the southern edge of the Laurentian Mixed Forest Province than it was in the early 1900s. The landscape’s extensive stands of mixed deciduous and coniferous forests have been replaced in many areas with towns and cities, industrial development, and intense recreational development, creating a more open landscape suitable to the shrub-loving thrasher. Yet, as Niemi’s (1978) work on the Little Sioux fire demonstrated, the species may have been widespread in this forested landscape before fire suppression efforts became commonplace.
Historically the Brown Thrasher is within a suite of species dependent on shrublands and open woodlots that benefited from wide-scale forest clearing and settlement in the eastern deciduous forest in the late 1800s and early 1900s. Farther west, in the Great Plains, it was originally confined to shrubby riparian corridors, but woody plantings along fencerows, shelterbelts, and farmsteads also provided expanded opportunities. More recently, in the latter half of the 20th century, Brown Thrashers have expanded into Canada’s Maritime Provinces and into southern Florida (Cavitt and Haas 2014). No significant distributional changes have been documented in the Upper Midwest and Great Lakes region.
*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.