- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular nesting species, migrant, and accidental winter visitor in Minnesota. The Hermit Thrush was a common species during the Minnesota Breeding Bird Atlas (MNBBA).
Wide distribution in the upper midwestern and northeastern United States and Canada, and south in the Appalachian Mountains to the state of Virginia (Figure 1). Also found throughout the western United States and Canada. The highest densities occur in northern Wisconsin, northern Michigan, and northeastern Minnesota, plus in many isolated patches of Ontario, Nova Scotia, and northern Colorado.
Assigned a Continental Concern Score of 7/20 by Partners in Flight.
Short-distance migrant, winters in eastern, southeastern, and southern areas of the midwestern United States to northeastern Mexico.
Omnivore; insects, small invertebrates, and fruit primarily foraged on the ground.
Cup nest on the ground or slightly elevated in the base of a bush or small tree.
The Hermit Thrush was historically described as nesting in the northern evergreen forests of Minnesota, south to Isanti and Pine Counties and northwest to Itasca Park and Roseau and Lake of the Woods Counties (Roberts 1932). Roberts reported confirmed nests with eggs or nestlings in Cass, Itasca, Lake, and St. Louis Counties as well as at Itasca Park, plus nesting activity at Mille Lacs (young out of nest).
Over 40 years later, Green and Janssen (1975) described a similar distribution, though they more precisely suggested its southern distribution in Minnesota extended to the cities of Onamia in Mille Lacs County and Sturgeon Lake in Pine County. They reported additional counties with confirmed nesting records beyond those reported by Roberts, including Carlton, Cook, Lake of the Woods, and Roseau Counties. They also cited older breeding observations from Isanti, Otter Tail, and Washington Counties, but they emphasized that no current records existed from these areas. Janssen (1987) depicted a similar breeding distribution to that presented by Green and Janssen and confirmed nesting in 9 counties since 1970: Aitkin, Beltrami, Clearwater, Crow Wing, Hubbard, Itasca, Koochiching, Lake, and St. Louis. Several years later, Hertzel and Janssen (1998) added Roseau County to the list of counties with confirmed nesting since 1970 but excluded Clearwater County.
The extensive coverage of the Minnesota Biological Survey (MBS) recorded 1,178 breeding season locations for the Hermit Thrush. These locations reinforced its primary breeding distribution in northeastern Minnesota, but extended the Hermit Thrush breeding range considerably to include many potential breeding locations south to Kanabec, Mille Lacs, Morrison, Pine, and Todd Counties. Western breeding observations included one location each in Mahnomen and Otter Tail Counties, plus many locations in eastern Becker, northeastern Marshall, and Roseau Counties.
The MNBBA detected 2,691 records of the Hermit Thrush distributed extensively throughout the Laurentian Mixed Forest Province and a few locations in the Tallgrass Aspen Parklands (Figure 2). The overall breeding distribution was similar to the observations of the MBS, but no observations were included from Kanabec County and only one possible record was reported in the far northeastern corner of Otter Tail County. The MNBBA solidified the understanding of the species’ extensive distribution throughout northern Minnesota, with observations in Beltrami, Koochiching, and Lake of the Woods Counties, all counties where MBS has not yet completed its inventories.
The Hermit Thrush was recorded from 24.5% (1,162/4,751) of all blocks, including confirmed nesting in 1.4% (66 blocks) (Figure 3; Table 1). The only confirmed county nesting record not previously reported was from western Minnesota in Becker County, while probable nesting was also suggested for Mahnomen and Morrison Counties.
The current distribution of the Hermit Thrush may be larger than previously presented for Minnesota; however, the increase in its distribution may result from the more extensive coverage of the MBS and the MNBBA. The species is relatively easy to identify by sight and sound, making it unlikely to be missed. Yet, a definitive conclusion on whether the species breeding range has expanded in Minnesota is unclear.
The probability map for the Hermit Thrush identified high densities in the Agassiz Lowlands Ecological Subsection of northern Minnesota (Figure 4). Otherwise the breeding population was relatively evenly distributed throughout northeastern and north-central Minnesota but with patches of higher density noted in the Tamarack Lowlands Ecological Subsection of southwestern St. Louis County.
In their review of the Hermit Thrush in North America, Dellinger et al. (2012) commented on its potential range expansions in British Columbia, in some New England states, and in the southern Appalachian Mountains, but they mentioned no changes in the midwestern United States. The Wisconsin breeding bird atlas also found a southern range extension for the species from what had been previously reported (Cutright et al. 2006). Brewer et al. (1991) and Cadman et al. (1987) also suggested recent southern extensions as a result of their breeding bird atlases for Michigan and Ontario, respectively. These extensions appeared to be colonizations of coniferous patches, such as in spruce-fir forests and pine plantations. Based on these data, the Hermit Thrush should be searched for in suitable conifer patches in central and southerly locations of Minnesota during the June breeding season.
*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.
|Breeding status||Blocks (%)||Priority Blocks (%)|
|Confirmed||66 (1.4%)||37 (1.6%)|
|Probable||436 (9.2%)||304 (13.0%)|
|Possible||659 (13.9%)||315 (13.5%)|
|Observed||1 (0.0%)||1 (0.0%)|
|Total||1,162 (24.5%)||657 (28.1%)|
Across its substantial range, nesting areas have been broadly described as coniferous, deciduous, and mixed forest types but with an affinity for conifers (Dellinger et al. 2012). The coniferous forest component has been emphasized in Minnesota by Niemi and Pfannmuller (1979), Green (1995), and Niemi and Hanowski (1992a, b) (Figure 5). Detections in the MNBBA point counts emphasized habitat associations in bogs, pine forests, and upland and lowland coniferous forests (Figure 6).
Intensive coverage of the Agassiz Lowlands area north of Upper Red Lake also indicated extensive use of black spruce-tamarack lowland and white cedar forests (Bednar et al. 2016). The National Forest Bird Monitoring (NFB) program (Niemi et al. 2016) found significantly higher use of black spruce-tamarack forests compared with all other forest types. The species was detected in almost every mature upland forest cover type but generally not in open habitats.
The North American population has been estimated at 70 million breeding adults by Partners in Flight (Rosenberg et al. 2016). The MNBBA breeding population was estimated as 986,000 breeding adults (95% confidence interval was 913,000 – 1,011,000), which is more than 3 times the 300,000 previously estimated by the Partners in Flight Science Committee (2013). Because of the wide distribution of the Hermit Thrush, Minnesota still represents a relatively small proportion of the species’ overall North American population.
The federal Breeding Bird Survey (BBS) in Minnesota indicated a significantly increasing breeding population of 1.42% per year from 1967 to 2015 (Figure 7). This increasing trend is also consistent with significantly increasing trends in Michigan (1.59% per year) and Wisconsin (1.18%), but its overall trend in Canada, the United States, and survey-wide are all non-significant, which suggests a stable population over this time period. However, a view of the BBS population trends of the Hermit Thrush across North America reveals a complex pattern of increases and decreases (Figure 8). Widespread declines occurred in much of the western United States, in British Columbia, and in Manitoba, but there were also many patches of increasing populations, such as in the Appalachian Mountains, in the Northern Rocky Mountains, and in Saskatchewan. Overall Partners in Flight (Rosenberg et al. 2016) estimated the North American population has increased by 35% from 1970 to 2014.
The NFB program revealed an inconsistent trend from 1995 to 2016 with a significantly increasing trend of 0.64% per year in the Chippewa National Forest and a significant decline of 1.13% per year in the Superior National Forest (Figure 9). This decline was similar to the decline of 1.51% per year in BBS routes in Manitoba from 1966 to 2015. This pattern in Minnesota is also illustrated in the BBS data, in which populations in a small part of northeastern Minnesota (where the Superior National Forest is located) are declining, but the remaining areas of the state have increasing populations (Figure 8).
Mean overall population densities in the Chippewa and Superior National Forests were 3.0 and 2.5 pairs per 40 ha, respectively. The highest mean densities observed during the NFB counts were 6.7 pairs per 40 ha in black spruce-tamarack lowland forests in the Chippewa. Densities were also high in mid-successional jack pine forests with a mean of 5.0 pairs per 40 ha in both the Chippewa and Superior National Forests. In the Agassiz Lowlands Ecological Province, the highest densities of the Hermit Thrush were found in semi-productive black spruce and tamarack bogs with an estimated mean density of 1.7 pairs per 40 ha.
The Hermit Thrush has a low Continental Conservation score of 7/20 by Partners in Flight (Rosenberg et al. 2016). The score is primarily due to its estimated high breeding population and its wide distribution in North America. Optimal breeding habitat appears to be lowland coniferous forests in Minnesota, but it is also commonly found in many other forested habitat types. Currently, many of its preferred habitat types are still common throughout its breeding range, but its habitat conditions may vary considerably across its North America populations.
In its review of bird species’ susceptibility to climate change, Langham et al. (2015) and the National Audubon Society (2015) identified the Hermit Thrush as a “climate threatened” species. Its models suggest a potentially dramatic shift northward and a loss of 73% of its current summer breeding range. In contrast, its winter range is predicted to expand northward.
Nesting success for the Hermit Thrush is susceptible to many factors common to most bird species. These include weather conditions, nest predation, habitat changes, diseases, and hazards of migration. Flaspohler et al. (2001) in Michigan and Manolis et al. (2002) in Minnesota both found decreased nesting success of Hermit Thrush near forest edges. Hanowski and Niemi (1995) found the species to abandon selectively logged riparian areas several years after logging, but Schulte and Niemi (1998) found that residuals left in logged areas were key to maintaining its presence within these areas.
At communication towers and windows, Longcore et al. (2013) and Loss et al. (2014), respectively, did not record the Hermit Thrush as a high-risk species in collisions, especially when compared with Swainson’s and Wood Thrushes. In a local study, Bracey (2011) detected 5 Hermit Thrush fatalities with window kills on Minnesota Point over five migration seasons at over 30 houses. This level of mortality was reasonably high compared with most species, but much lower than the 14 Swainson’s Thrush fatalities. Dellinger et al. (2012), however, also identified several high mortality occurrences of the Hermit Thrush at buildings and residences.
Obviously, considerable research is still necessary to better elucidate factors associated with Hermit Thrush ecology and conservation throughout its range in North America. Currently, the Hermit Thrush appears to be maintaining a stable population in Minnesota and in North America.
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Bednar, Joshua D., Nicholas G. Walton, Alexis R. Grinde, and Gerald J. Niemi. 2016. Summary of Breeding Bird Trends in the Chippewa and Superior National Forests of Minnesota – 1995–2016. Natural Resources Research Institute Technical Report NRRI/TR-2016/36.
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