- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular summer resident and migrant; regular in winter in the southern half of the state. The Brown-headed Cowbird was an abundant species during the Minnesota Breeding Bird Atlas (MNBBA).
Distributed throughout much of the United States, southern Canada, and northern Mexico, the Brown-headed Cowbird is abundant throughout the central U.S. and Canadian Prairie Provinces. It reaches its highest breeding densities in central North Dakota (Figure 1).
Assigned a Continental Concern Score of 7/20 by Partners in Flight.
Northern populations, including in Minnesota, are short-distance migrants that winter in the southern United States and Mexico; southern populations are year-round residents.
A ground forager consuming primarily seeds, some grains, and insects.
A brood parasite, the Brown-headed Cowbird female lays her eggs in the nests of other species.
The Brown-headed Cowbird is a widespread and abundant breeding resident in Minnesota. Maligned for its parasitic nesting habits, it was described nearly 100 years ago by Roberts (1932) as “all too abundant in every section of Minnesota.” Although generally considered a beneficial species among farmers (Bent 1958), Roberts (1932) stated that “its practice of foisting its eggs and the rearing of its young upon other birds, generally of equal or greater value than itself, renders it undesirable.” Originally confined to the grasslands of central North America, the cowbird began its eastward expansion in the early 1800s as European settlers cleared the deciduous forests. By the late 1800s it already was deemed by Roberts to be statewide in distribution. His sweeping assessment, however, makes no distinction of its relative abundance in different regions of the state. No doubt, at the time the cowbird was far less abundant in the extensively forested landscape of northern Minnesota than it was in the southern and western agricultural regions of the state.
Green and Janssen (1975) make brief mention of the species’ distribution, commenting only that it was a breeding resident throughout the state. Several years later, Janssen (1987) described it as being most numerous in Minnesota’s wooded regions, where nesting songbirds were abundant. This statement, however, seems contrary to the species’ origin in the western grasslands and to data collected by the federal Breeding Bird Survey (BBS), which illustrates higher abundances in western and southern Minnesota (Figure 1). Janssen included a map that identified 36 counties where the species had been confirmed parasitizing songbird nests since 1970. Hertzel and Janssen (1998) later added an additional 16 counties to the list of confirmations.
Field biologists with the Minnesota Biological Survey have reported a total of 2,142 breeding season locations of Brown-headed Cowbirds. Although their records are widely distributed across the state, their distribution map is the first to depict the species relatively sparse distribution in the northeastern and north-central regions of the state. Indeed, their records only include one location in Cook County, while none were reported in Lake County (Minnesota Department of Natural Resources 2016).
The MNBBA reported 5,170 cowbird records in 55.6% (2,646/4,759) of the atlas blocks that were surveyed and in 77.7% (1,816/2,337) of the priority blocks. Breeding parasitism was confirmed in 5.0% (240) of the surveyed blocks (Figures 2 and 3; Table 1). Birds were observed in all 87 Minnesota counties, and breeding evidence was gathered in 68 counties; Chippewa County was included because one block with confirmed nesting straddled both Chippewa and Yellow Medicine Counties. Widely distributed across the Prairie Parklands, Tallgrass Aspen Parklands, and Eastern Broadleaf Forest Provinces, cowbirds were more sparsely distributed in the eastern and far northern counties of the Laurentian Mixed Forest Province. Indeed, they were reported from only four blocks in Cook County and six blocks in Lake County.
Although the cowbird remains least abundant in Minnesota’s northern forest, its broad habitat requirements allowed it to exploit the landscape as industrial and residential development expanded. A similar pattern occurred decades earlier as cowbirds expanded east from their primary habitat in the Central Plains. They spread throughout the eastern United States in the 1800s and early 1900s and through the southeastern Canadian provinces in the early half of the twentieth century. A similar expansion occurred westward into the Pacific Northwest (Lowther 1993).
*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.