- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular breeding resident and migrant; the Clay-colored Sparrow was a common species during the Minnesota Breeding Bird Atlas (MNBBA).
The Clay-colored Sparrow is confined to the interior of North America. It is found as far west as the mountain valleys of eastern British Columbia and Alberta, east to southern Ontario and Quebec, and south through the northern Great Plains and Great Lakes region. Small, disjunct populations occur north along Hudson Bay and James Bay. Abundant throughout much of its breeding range, high breeding densities are found in Canada’s Prairie Provinces and North Dakota (Figure 1).
Assigned a Continental Concern Score of 10/20 by Partners in Flight.
A short-distance migrant that winters primarily in the grasslands of southern Texas, southern Baja California, and the highlands of northern and central Mexico.
An omnivorous ground forager that consumes a variety of seeds and invertebrates.
An open-cup nest usually placed in a low shrub.
When Roberts wrote his account of the Clay-colored Sparrow in 1932, he considered it an abundant summer resident breeding throughout the state. “Indeed, nowhere in the state, except in the deep unbroken forest, is the Clay-colored Sparrow without a goodly representation.” He noted it was “especially abundant in the poplar belt bordering the Red River Valley on the east.” In the more densely forested landscape of north-central and northeastern Minnesota, it was equally numerous wherever “there are clearings, old ‘burns,’ windfalls, or other openings.” Confirmed nesting records (nests with eggs) stretched from Fillmore County in southeastern Minnesota; north to Hennepin, Isanti, McLeod, and Sherburne Counties in east-central Minnesota; west to Big Stone County; and north to Leech Lake and Itasca State Park and to Kittson, Marshall, Norman, Pennington, and Polk Counties in northwestern Minnesota. Inferred nesting reports (nests or adults carrying food) were reported in Goodhue and Mower Counties in southern Minnesota and the Mille Lacs region in northern Minnesota.
More than four decades later, Green and Janssen (1975) described the species’ statewide distribution but noted it was “very scarce” in southern Minnesota. Although Roberts had reported the sparrow from several southern counties in the late 1800s and early 1900s, no recent records had been reported south of Dakota and Lyon Counties. Janssen (1987) provided even more details regarding the species’ statewide distribution, noting it occurred primarily north of a line from northern Houston County west to Lincoln County. Abundance increased moving north except in the most densely forested regions of north-central and northeastern Minnesota. His distribution map excluded most of the southern tier of counties, although recent observations suggest that the species might be slowly reoccupying the region. He identified 21 counties in which nesting had been confirmed since 1970. Hertzel and Janssen (1998) later added another 11 counties to the list.
Field staff with the Minnesota Biological Survey (MBS) documented a total of 1,562 breeding season locations of the Clay-colored Sparrow statewide, including many records in southwest and south-central counties. Breeding season locations were identified in every county along the Iowa border except Fillmore. The species was still rare, however, in the Blufflands of southeastern Minnesota (Minnesota Department of Natural Resources 2016).
MNBBA participants reported 3,872 Clay‑colored Sparrow detections in 40.5% (1,933/4,767) of the surveyed atlas blocks and in 53.3% (1,246/2,338) of the priority blocks. Breeding evidence was documented in 187 blocks (Figures 2 and 3; Table 1). The species was reported from every county in the state and was confirmed breeding in 56 counties. Records were least common in north-central and far northeastern Minnesota as well in south-central and far southeastern Minnesota. Nevertheless, breeding was confirmed in several southern counties excluded from the distribution map presented by Hertzel and Janssen (1998), including Fillmore, Freeborn, and Jackson.
The MNBBA predicted distribution map predicted the highest breeding densities should be encountered in northwestern Minnesota, especially in the Tallgrass Aspen Parklands Province and in the Hardwood Hills and the Pine Moraines and Outwash Plains Subsections in west-central Minnesota (Figure 4). Shrubby wetlands scattered throughout the Agassiz Lowlands Subsection north of Red Lake also are predicted to support high densities. The area with the most suitable habitat in northeastern Minnesota is the location of the 2007 Ham Lake fire on the north end of the Gunflint Trail in Cook County. As Roberts (1932) noted earlier, the species is numerous in forest openings created by former fires.
The Clay-colored Sparrow appears to now occupy much of the state where it occurred more than one hundred years ago. Although it was scarce across southern Minnesota in the mid-1900s, it is now a regular species throughout that region, albeit in lower numbers than are encountered farther north. It may also be more common in the southern and western regions of the Laurentian Mixed Forest Province than it was decades ago because development has fragmented much of the formerly extensive forest landscape in the region.
Since the early 1900s, the Clay-colored Sparrow has gradually expanded its range to the north and east throughout North America as logging and farming activities opened up densely forested landscapes. The species expanded its range east across Ontario over a period of 75 years (Cadman et al. 2007). It reached southwestern Quebec in 1960 and was documented as a breeding species in 1975. Now it is broadly distributed throughout the southern third of the province (Quebec Breeding Bird Atlas 2016) and continues to expand eastward to the Maritime Provinces and New England (Grant and Knapton 2012). Along the northwestern periphery of its breeding range, in British Columbia, populations are expanding further west throughout the southern region of the province (Ryder 2015).
*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||187 (3.9%)||135 (5.8%)|
|Probable||689 (14.5%)||511 (21.9%)|
|Possible||1,052 (22.1%)||598 (25.6%)|
|Observed||5 (0.1%)||2 (0.1%)|
|Total||1,933 (40.5%)||1,246 (53.3%)|
Shrubs in an otherwise open landscape are the defining feature of the Clay-colored Sparrow’s breeding habitat. The species may occur in dry shrubby uplands, such as forest clearcuts, young conifer plantations, dry-to-mesic grasslands, or in wet lowlands, such as alder-willow thickets or along shrubby drainageways (Figure 5). In Minnesota, habitats within 200 m of MNBBA point counts where the Clay-colored Sparrow was detected included predominantly grasslands followed by cropland, marsh, shrub wetlands, and pine-oak barrens (Figure 6).
Although the species has adapted to a variety of shrub-dominated communities, it is considered a grassland-obligate specialist. In the northern Great Plains it is strongly associated with grasslands interspersed by low shrub communities that are dominated by western snowberry (Grant and Knapton 2012). Clay-colored Sparrows are common in fields enrolled in the Conservation Reserve Program (CRP). Such sites are often planted with alfalfa and sweet clover, which grow in dense clusters and provide some of the same structural features as low shrubs. The density and cover of herbaceous vegetation and ground litter have also been demonstrated to be important features in some studies (Dechant et al. 2002).
Although shrubs define the sparrow’s breeding territory, suitable foraging areas must be located nearby. Short, sparse vegetation is critical and can include cultivated fields, pastures, dry prairies, and restored grasslands (Dechant et al. 2002).
Studies provide mixed conclusions regarding the species’ sensitivity to patch size and edge effects. At least one study conducted in western Minnesota suggested that nest success may be higher on large, contiguous grassland tracts (Johnson and Temple 1990). In particular, nest predation was lower on large grasslands (130–486 ha) than on small grasslands (16–32 ha). More recently, Winter and his colleagues examined the influence of patch size and landscape composition on the density and nesting success of Clay-colored Sparrows in northwestern Minnesota and eastern North Dakota (Winter et al. 2006). In this area of prime breeding habitat, the species’ response (i.e., breeding density and nesting success) to patch size varied among regions and years. The authors concluded that patch size may not be as important to the species as local habitat structure and landscape composition.
Data collected by the federal Breeding Bird Survey (BBS) have been used to generate a continental population estimate of approximately 64 million breeding adults; nearly 85%–90% of which occur in Canada (Rosenberg et al. 2016; Partners in Flight Science Committee 2013). In 2013 approximately 3.2% of the continental population was estimated to reside in Minnesota, which generates a current population estimate of 2 million individuals. The MNBBA-derived population estimate was considerably higher at 3.4 million individuals (95% confidence interval of 3.1 to 3.8 million) and reflects the more intensive sampling conducted by the MNBBA, especially in regions of the state that support high Clay-colored Sparrow breeding densities, such as the Agassiz Lowlands Subsection.
Minnesota lies on the eastern periphery of the Clay-colored Sparrow’s core breeding range in the northern Great Plains. An average of only 7 sparrows is detected per BBS route in the state each year. This compares to an average of 51 sparrows per route in the Prairie Pothole Region (Sauer et al. 2017). Local breeding densities can be as high as 24–28 pairs per 40 ha (Grant and Knapton 2012). In prime habitat in northwestern Minnesota, such as in Becker, Clay, and Mahnomen Counties, an average of 30.4 pairs per 40 ha was observed (Winter et al. 2005). A study of CRP fields in 12 western Minnesota counties documented an average of 15 pairs per 40 ha (Hanowski 1995). In the forested landscapes in north-central and northeastern Minnesota, an average of only 0.24 pairs per 40 ha were documented in the Chippewa National Forest and 0.04 pairs per 40 ha in the Superior National Forest (Niemi et al. 2016).
BBS data demonstrate a statistically significant, long-term population decline of 1.14% per year from 1966 to 2015 throughout North America (Sauer et al. 2017). The level of the decline has slowed somewhat since 2005 to an average annual decline of 0.32% per year. Overall, from 1970 to 2015, the species has experienced a cumulative decline of 43% (Rosenberg et al. 2016). The downward trend is similar in Minnesota, where the species has experienced a significant annual decline of 0.62% per year since 1967 (Figure 7).
The decrease in the rate at which the species is declining in North America in recent years may be due, in part, to the large-scale enrollment in the United States of former cropland into the Conservation Reserve Program (CRP) (Grant and Knapton 2012). Although the Clay-colored Sparrow utilizes CRP acres in Minnesota, enrollment appears to have had little impact on the state’s population. Either the initial enrollment in CRP was not significant enough to replace the continuing loss and degradation of grassland habitats across the state, or other significant factors are negatively impacting Minnesota’s Clay-colored Sparrow population.
Despite declining population trends, overall conservation threats to the Clay-colored Sparrow are considered low to moderate. Partners in Flight assigned it a moderate Continental Concern Score of 10/20, a score influenced largely by the sparrow’s significant population decline. The species is not considered a conservation priority at the state or federal level.
Loss of native grassland/shrub habitat is considered the largest threat to the Clay-colored Sparrow. Although the large-scale loss of grassland habitats, particularly in the United States, occurred 50–100 years ago, losses continue. The species has adapted to restored grasslands, but the availability of this habitat is subject to the vagaries of commodity markets. When corn and grain prices are high, fewer farmers enroll croplands into set-aside programs such as CRP. Even those native and restored grasslands that remain require management to reduce invasive species and prevent succession.
Compounding the loss of habitat are the predicted impacts of a warming climate. Although the species was originally assessed to have a low vulnerability to climate change, a more recent analysis by the National Audubon Society classified the species as “climate threatened.” The Clay-colored Sparrow was predicted to lose 82% of its current breeding range by the year 2080 (Langham et al. 2015; National Audubon Society 2016).
Specific management recommendations focus on maintaining sufficient shrub coverage. One study suggested that relatively low shrub coverage was needed to attract Clay-colored Sparrows. Because they select grasslands that are interspersed with woody vegetation, as little as 3% shrub cover raised the probability of Clay-colored Sparrows being present to 69%; 20% shrub cover raised the probability to 95% (Madden et al. 1999). Achieving this balance can be accomplished by allowing grasslands to remain idle long enough to encourage some shrubby cover. When burning or mowing occurs, patches of shrubs should be identified and protected from treatment (Dechant et al. 2002).
Long-term conservation strategies to protect and restore Minnesota’s grasslands and wetlands, including the Minnesota Prairie Conservation Plan (Minnesota Prairie Plan Working Group 2011), are critical to help sustain Clay-colored Sparrow populations in Minnesota’s grassland communities. Although it is an adaptable species, the endangered grasslands of the northern Great Plains still support the core of the species’ population. This “plainly garbed, inconspicuous little bird” (Roberts 1932) deserves as much consideration in the protection and management of our prairie landscape as the more charismatic species that garner more attention.
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