- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular summer resident and migrant; a small number of birds were regularly seen each winter through the 1990s. Since 2000 it has been reported only 4 of 16 winters. The Brewer’s Blackbird was an uncommon species during the Minnesota Breeding Bird Atlas (MNBBA).
Restricted primarily to western North America, the northeastern periphery of the species’ range extends across the Great Lakes region. Highest breeding densities are found in the western Great Basin and coastal California (Figure 1).
Assigned a Continental Concern Score of 10/20 by Partners in Flight and designated a Common Bird in Steep Decline.
Populations in central Canada and the north-central United States are short-distance migrants that winter in the southern United States and Mexico; populations in western North America are year-round residents.
An omnivorous ground forager that feeds on a wide variety of terrestrial insects as well as weed seeds and waste grain.
An open cup that may be placed on the ground or in trees and shrubs; nests in colonies that number just a few pairs to more than 100 pairs.
Prior to the 1900s, the Brewer’s Blackbird was principally a species of the western United States The eastern limit of its breeding range was considered the Red River valley of Minnesota. Indeed, Roberts (1932) wrote that the species was “abundant in the Red River valley since the earliest records for that region.” A species of open habitats, the western limit of the Eastern Broadleaf Forest was considered an ecological boundary. But as small communities, farms, roads, and cities expanded during European settlement, the forested landscape opened and Brewer’s Blackbirds began their eastward expansion.
The birds were first discovered nesting in Minneapolis in 1914 and in Isanti and Sherburne Counties in 1915. When Roberts wrote his account of the species in 1932, the Brewer’s Blackbird had become a common breeding species in all but the most southern counties of the state and the extensively forested north country. A 1928 report of several colonies in Pine and Carlton Counties, as well as along the Iron Range in central St. Louis County, led him to speculate that this consumer of waste grain had followed the railroads north, and it was only a matter of time before it would be well established further north. At the time, confirmed nesting records (nests with eggs or young) were available from five counties: Douglas, Hennepin, Kittson, Marshall, and Polk. Inferred nesting (feeding young and fledglings) was reported from Isanti and Sherburne Counties.
The range expansion witnessed in Minnesota was underway further east as well. By 1926, for example, observers documented an influx of birds in south-central Wisconsin (Williams 1958). Taking advantage of the clearing of the eastern forests, the spread of agriculture, and the construction of railroads and highways, Brewer’s Blackbirds moved nearly 1,200 km east across the central Great Lakes Region during the first half of the twentieth century, advancing at a rate of nearly 18 km/year. At the same time they also expanded their range into western Canada, moving nearly 300 km further north into the southern Northwest Territories (Martin 2002).
By 1975, Green and Janssen reported that the species had become a breeding resident throughout the state, except in the heavily forested regions of the northern counties, from Lake of the Woods east to the Pigeon River. Despite its scarcity in this region, breeding records were available from Kittson County, east to Hibbing in St. Louis County, and from Tofte in Cook County. Brewer’s Blackbirds were also scarce south of the Minnesota River, particularly in the southwest.
A few years later Janssen (1987) included a range map in his updated account that identified 19 counties where nesting had been confirmed since 1970. Hertzel and Janssen (1998) would later add one more county to the list; all but two of the 20 counties where nesting had been confirmed were north of the Minnesota River (Scott and Dakota).
By 2014, field staff with the Minnesota Biological Survey documented 284 breeding season locations for Brewer’s Blackbirds. The majority of sites were in the northern half of the state and in counties bordering the Minnesota River Valley (Minnesota Department of Natural Resources 2016).
The MNBBA participants reported 728 Brewer’s Blackbird detections in 11.4% (539/4,747) of the atlas blocks that were surveyed and in 15.6% (364/2,337) of the priority blocks. Breeding was confirmed in 126 of the surveyed blocks (Figures 2 and 3; Table 1). Reports were gathered from 72 of Minnesota’s 87 counties, and breeding was confirmed in 44 counties, including 8 south of the Minnesota River. One block with confirmed breeding straddled 2 counties: Carver and Scott. The species was most abundant in the northern Red River valley, including the Tallgrass Aspen Parklands Province. Otherwise it was scarce in the extreme southwest, southeast, and northeast corners of the state. The species is, however, fairly well established in a number of counties south of the Minnesota River, stretching from Dakota County in the east to Redwood and Yellow Medicine Counties further west.
For a species found in open landscapes, which abound throughout all but the less settled and heavily forested counties of northern Minnesota, its sporadic distribution outside of the northwestern counties is somewhat surprising. Although it seems to have exploited some developed areas, including the Brainerd Lakes region of central Minnesota and the northern Iron Range, it remains an uncommon species throughout much of the state.
The Brewer’s Blackbird’s range expansion in the first half of the twentieth century was facilitated by forest clearing and the development of transportation corridors (Martin 2002). Further range expansion since that time has been limited. Results from both the first and second breeding bird atlases conducted in Michigan suggest that “the initial surge during the colonization phase” of the early 1900s “has waned” (Chartier et al. 2013). Ontario also witnessed a decline in the species occurrence in the province during the second atlas, suggesting that “numbers may now be stabilizing” (Cadman et al. 2007).
*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.