- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular breeding resident and migrant, the Sora was a uncommon species during the Minnesota Breeding Bird Atlas (MNBBA).
The Sora is widely distributed throughout Canada, from central British Columbia and the Northwest Territories east to Nova Scotia and across the upper midwestern and western United States south through New Mexico and Arizona. The core of the Sora’s breeding range is located in the northern Great Plains of the United States and the Prairie Provinces of Canada (Figure 1).
Ranked a species of High Concern by the North American Waterbird Conservation Plan and assigned a Continental Concern Score of 9/20 by Partners in Flight.
Medium- to long-distance migrant that winters along the southern coast of the United States south through Central America and northern South America.
Probes the vegetation and wetland substrate for aquatic invertebrates and seeds.
A woven basket of aquatic vegetation attached to surrounding vegetation; often has an overarching canopy and a small ramp leading up to the nesting platform.
In the late 1800s, Hatch (1892) described the Sora as Minnesota’s most abundant rail, breeding in “nearly all parts” of the state. It was so common, he noted, that in Minneapolis one only had to walk 15 minutes in nearly any direction at sunset to encounter the bird. It was particularly abundant in a narrow tamarack swamp on the north shore of Lake Calhoun, just west of downtown Minneapolis.
Forty years later, the species’ abundance appeared to have changed very little. Roberts (1932) commented that “every marsh and grass-bordered lake harbors a considerable number of these birds.” During the fall migration, the Sora could even be seen feeding in upland fields and on brushy hillsides, especially in landscapes where wetlands were not common. Despite its abundance and widespread distribution, nesting of this secretive marsh bird was only confirmed in six different counties: Cass, Crow Wing, Hennepin, Isanti, Kittson, and Polk.
Green and Janssen (1975) and Janssen (1987) both described the Sora as a statewide resident, noting that it was rare or absent in heavily forested regions of northeastern and north-central Minnesota. Janssen identified 19 counties where nesting had been confirmed since 1970, only 3 of which were in the heavily cultivated landscape south of the Minnesota River. Later, Hertzel and Janssen (1998) would add another 6 counties to the list, only one of which was south of the Minnesota River.
Field biologists with the Minnesota Biological Survey have identified 408 breeding season locations since their field surveys began in the late 1980s. Records were least abundant in northeastern Minnesota and, with the exception of the Prairie Coteau of southwestern Minnesota, were rare in all counties south of a line between Washington County in the east and Lac qui Parle County in the west (Minnesota Department of Natural Resources 2015).
During the MNBBA, observers reported 839 Sora records in 13.5% (644/4,762) of the surveyed atlas blocks and in 15.3% (358/2,337) of the priority blocks. Breeding was confirmed in 13 blocks (Figures 2 and 3; Table 1). Reports of the Sora came from 84 of Minnesota’s 87 counties; the species was absent only in Blue Earth, Dodge, and Watonwan Counties in south-central Minnesota. Breeding evidence was documented in 12 counties, all north of the Minnesota River, including 1 record as far north as Cook County. Of the list published by Hertzel and Janssen (1998), 6 counties were additions: Clay, Cook, Douglas, Meeker, Sherburne, and Todd. The Sora was most abundant in central Minnesota, from Washington County west to Yellow Medicine County and north through the grasslands and parklands of northwestern Minnesota and the northern portion of the Eastern Broadleaf Forest. The species occurred in more than twice as many blocks (644) as its relative, the Virginia Rail (307).
The statewide probability map generated with MNBBA data predicted a low breeding density of the Sora throughout western and central Minnesota (Figure 4). Higher densities were predicted in the wetland basins located immediately west of Red Lake, in the Tallgrass Aspen Parklands, and in the glacial outwash plains southwest of Leech Lake.
Although the Sora is likely not as abundant as it was in the time of Hatch and Roberts, it remains a widely distributed species. It may even be a little more common in northeastern Minnesota than Green and Janssen believed. Nevertheless, gone are the days when one could walk out the front door and 15 minutes later find a small population of Sora rails.
Throughout the Sora’s North American breeding range, the extent of its distribution has changed little in the past 100 years. Still widespread, its occurrence has become more localized in response to an extensive loss of wetland habitats (Melvin and Gibbs 2012). States and provinces that have completed two atlases have noticed little overall change in the species’ distribution, with the exception of Ohio, where the Sora appeared to be slowly expanding the southern periphery of its breeding range (Rodewald et al. 2016).
Like other secretive marsh birds, the Sora presents challenges to field biologists, and long-term studies regarding its life history, population dynamics, and breeding biology are often limited. Two in-depth studies of the Sora and the Virginia Rail conducted in Minnesota and Iowa remain among the most significant life history studies on both species. The first was conducted in Ramsey County in the early 1950s by Pospichal and Marshall (1954); the second was conducted by Kaufmann at a number of sites in Iowa and in Anoka County, Minnesota, in the 1960s (Kaufmann 1971, 1977, 1983, 1987, 1988, 1989).
*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.