- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular breeding resident and migrant, occasionally reported during the winter months. The Savannah Sparrow was an abundant species during the Minnesota Breeding Bird Atlas (MNBBA).
Breeding range spans from Alaska east across all of Canada, south through the Pacific Northwest and northern California, and east across the northern Great Plains, the Great Lakes, New England, and the Appalachian Mountains. Resident populations are present in southern California, Baja California, and central Mexico. Populations reach their highest breeding densities in the northern Great Plains of the United States and in Canada’s Prairie Provinces (Figure 1).
Assigned a Continental Concern Score of 8/20 by Partners in Flight.
A short- to medium-distance migrant that winters in the southern United States and Central America.
An omnivorous ground forager that feeds on a variety of seeds and insects.
An open-cup nest placed in a shallow depression on the ground, usually tucked within a mound of vegetation or well-hidden by a canopy of forbs and grasses. A small tunnel underneath the grasses may lead to the nest.
In the late 1800s and early 1900s, Roberts (1932) described the Savannah Sparrow as a common breeding resident throughout Minnesota wherever suitable habitats were present. This diminutive sparrow, with its distinctive buzzy song, was abundant “on the western prairies, where it inhabits not only the lowlands but also upland thickets of rose-bushes, hazel, and wolfberry.” It was found in northern Minnesota, where it was “confined to meadows adjoining lakes and marshy land and to old grass-grown clearings.” Despite its abundance and widespread distribution, confirmed nesting records (nest with eggs or young) were few and were confined primarily to western and east-central Minnesota: Grant, Hennepin, Kittson, Otter Tail, Pennington, Polk, Ramsey, and Wilkin Counties. An inferred nesting record (fledged young) was available from Itasca County.
A widespread, abundant, and complex species, the Savannah Sparrow displays considerable morphological variation across its range. The most variable trait is the darkness of the plumage. Indeed, taxonomists have debated the delineation of different species and subspecies for years. Roberts (1932) sent a series of 32 specimens collected in Minnesota to the U.S. Biological Survey for examination. All but one were identified as belonging to the eastern subspecies, Passerculus sandwichensis savanna, although their plumage appeared intermediate between the lighter western subspecies, P. s. alaudinus, and the darker eastern subspecies. Five specimens collected in the late 1800s in Pembina, North Dakota, were all identified as belonging to the western subspecies. Today, a total of 17 subspecies are recognized, and Rising (2010) has recently proposed that these be collapsed into four distinct species. Minnesota birds would remain as the nominate species, Passerculus sandwichensis.
Decades after Roberts’s observations, both Green and Janssen (1975) and Janssen (1987) noted that the species was a breeding resident throughout Minnesota wherever “low-lying grassy fields” were present. Janssen included a statewide distribution map that identified 13 counties where nesting had been confirmed since 1970. Long considered a species of the western grasslands, intensive field surveys in Minnesota’s peatlands in the 1980s revealed that the Savannah Sparrow was very common in open, unforested peatlands. It dominated the avifauna associated with the “matted sedge and heath vegetation of the ombrotrophic peatlands” (Niemi and Hanowski 1992).
The species’ statewide distribution was further confirmed by the Minnesota Biological Survey (Minnesota Department of Natural Resources 2016). Beginning in the late 1980s, Minnesota Biological Survey field staff reported a total of 1,465 breeding season locations from all corners of the state. By 1998, Hertzel and Janssen had documented 21 counties where nesting had been confirmed since 1970.
MNBBA participants reported a total of 4,012 Savannah Sparrow records from 45.7% (2,189/4,789) of the surveyed atlas blocks and from 62.8% (1,469/2,338) of the priority blocks. Breeding was confirmed in 166 blocks (Figures 2 and 3; Table 1). Although the species was least abundant in the far northern reaches of the state, it was reported from all 87 Minnesota counties. Breeding evidence was collected from 53 counties.
Probable and confirmed Savannah Sparrow records were especially common in the northwest corner of the state. This is the same region where the MNBBA predicted distribution map predicts the highest breeding densities to occur, as well as across a relatively narrow band in central Minnesota that stretches from Chisago and Pine Counties west to Pope, Douglas, Otter Tail, and southern Becker Counties (Figure 4). Moderately abundant throughout the western, central, and southeastern regions, Savannah Sparrow breeding densities are predicted to be lowest in northeastern and north-central Minnesota, especially the far eastern Arrowhead counties of Cook and Lake, and in the Twin Cities metropolitan region. The importance of peatlands to the species is further evidenced by the relatively high breeding densities predicted in portions of the Agassiz Lowlands Subsection.
Knowledge regarding the range of habitats used by the Savannah Sparrow in Minnesota has grown, but the species’ overall distribution appears relatively unchanged since Roberts (1932) described it as a common summer resident in the early 1900s. In their comprehensive review of the species, Wheelwright and Rising (2008) noted only two historical changes to its distribution: its extirpation from northwestern Arkansas and the apparent extirpation or major decline of a population that breeds in the southwest, in the riparian marshes at the mouth of the Colorado River.
In the north-central United States, few minor changes in distribution have been noted over the years. The species was rare in Ohio in the early 1900s but was widespread throughout the state by the 1930s (Rodewald et al. 2016). Historic accounts in Michigan reported that the sparrow was local and uncommon in the southern Lower Peninsula but was widespread by the 1970s (Chartier et al. 2013). In Wisconsin, the Savannah Sparrow has always been widespread and abundant in all but the most densely forested and densely populated regions (Cutright et al. 2006). South Dakota’s population, however, has been increasing, with a notable range expansion in the northwest (Drilling et al. 2016).
*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||166 (3.5%)||131 (5.6%)|
|Probable||785 (16.4%)||636 (27.2%)|
|Possible||1,234 (25.8%)||698 (29.9%)|
|Observed||4 (0.1%)||4 (0.2%)|
|Total||2,189 (45.7%)||1,469 (62.8%)|
An inhabitant of open landscapes dominated by grasses and sedges, the Savannah Sparrow finds suitable habitats in a wide range of cover types. In the Upper Midwest and northern Great Plains, it may be found in sites ranging from native prairies to lightly grazed pastures, alfalfa hayfields, and lands enrolled in the Conservation Reserve Program (CRP) to wet meadows and sedge fens (Figure 5). In other parts of its range, it occupies tundra, salt marshes, and coastal dunes (Swanson  2002; Wheelwright and Rising 2008). The two primary habitats observed within 200 m of MNBBA point counts where the Savannah Sparrow was detected were upland grassland and cropland (Figure 6).
The most important predictors of the species’ presence appear to be grasses and sedges that are short to intermediate in height, an intermediate vegetation density, and a well-developed litter layer for nest concealment. Sites with extensive trees and shrubs are avoided. Most sites have some herbaceous cover in addition to grasses and sedges. Mesic sites are preferred over more dry, arid sites (Swanson  2002).
Some studies have documented the Savannah Sparrow’s sensitivity to habitat fragmentation. Although the species may be found on sites that are 5 ha or smaller, several studies have demonstrated its greater abundance on larger tracts. Biologists in Illinois classified the species as highly sensitive to fragmentation when they failed to find any birds on tracts smaller than 10 ha (Herkert 1991a, b, c). A study on native prairie tracts in western Minnesota found that the Savannah Sparrow was more abundant on larger tracts where the distance to the nearest woodland edge was greater, presumably because rates of nest predation and cowbird parasitism were lower (Johnson and Temple 1986, 1990).
Monitoring data collected by the federal Breeding Bird Survey (BBS) were used by biologists to generate a North American population estimate for the Savannah Sparrow of 170 million breeding adults (Rosenberg et al. 2016). That estimate is unchanged since 2013, when Minnesota was estimated to support 2.4% of the continental population, or 4 million adults (Partners in Flight Science Committee 2013). The statewide population estimate using MNBBA is 6.9 million adults (95% confidence interval of 6.1 to 7.5 million).
Although Minnesota supports a large population of Savannah Sparrows, it is surrounded by states and provinces with even larger populations. The average number of sparrows detected on BBS routes in Minnesota is 24. In Wisconsin the average is 66 and in North Dakota it is 32. Routes in southern Saskatchewan support an average of 85 sparrows per route. Primarily a species of the northern Great Plains, the Savannah Sparrow’s breeding densities drop significantly immediately south of Minnesota. The average number of birds detected along BBS routes in Iowa is just 2 (Sauer et al. 2017).
Local breeding densities of 28 pairs per 40 ha were reported in Wisconsin and 56 pairs per 40 ha in Michigan (Wheelwright and Rising 2008). In North Dakota, densities ranged from approximately 2 pairs per 40 ha to 20 pairs per 40 ha. Some of the highest densities were reported in rights-of-way, and the lowest densities in cropland, wetlands, and woody sites (Igl et al. 2006). In Minnesota 14 pairs per 40 ha were reported on CRP lands in western Minnesota (Hanowski 1995) and 20 pairs per 40 ha in open black spruce bogs in the Red Lake peatlands (Nevers et al. 1981).
Throughout the BBS survey region in southern Canada and the United States, Savannah Sparrow populations have experienced a significant annual decline of 1.36% from 1966 to 2015 (Sauer et al. 2017). From 1970 to 2014, the population has experienced a cumulative decline of 40% (Rosenberg et al. 2016). In Minnesota, the decline has been steeper, with a significant decrease of 2.33% per year overall; the rate of decline has nearly doubled in the 10-year reporting period of 2005–2015 to 4.33% per year (Figure 7). The declines are widespread throughout the BBS region (Figure 8).
As the eastern deciduous forests were cleared for agriculture in the 1800s, the Savannah Sparrow benefitted and populations flourished. But as many agricultural areas were abandoned and succeeded to forest cover (e.g., in the New England states) or were cleared for development, the availability of suitable sites has declined. In addition, agricultural practices on remaining lands have intensified significantly, as large‑scale row crops are favored over smaller dairy farms and hayfields, again providing fewer nesting opportunities (Wheelright and Rising 2008). The advent of conservation programs, particularly the Conservation Reserve Program (CRP), has provided improved habitat opportunities, but the short-term contracts that dominate the program are susceptible to the vagaries of the commodity market. The importance of these sites to many species of grassland birds was demonstrated by an examination of 30 CRP sites in western Minnesota in 1993 (Hanowski 1995). Present on 90% of the sites surveyed, the Savannah Sparrow was one of the sites’ six most common breeding birds. Other potential contributors to population declines include the sparrow’s sensitivity to disturbance at the nesting site and its exposure to agricultural pesticides (Wheelright and Rising 2008).
Although its population decline mirrors that of many other grassland birds, the Savannah Sparrow is not considered a conservation priority at either the state or federal level. Its large population size and wide-ranging distribution and the absence of imminent threats to its breeding and wintering habitat place it low on the priority list. Partners in Flight assigned the species a Continental Concern Score of only 8/20 (Rosenberg et al. 2016). Warming temperatures, a threat to many North American birds, do not appear to be a significant concern for the Savannah Sparrow. An initial assessment ranked the species’ vulnerability to climate change as low (North American Bird Conservation Initiative 2010).
Specific management recommendations for the species focus on promoting the protection and restoration of large tracts of suitable habitat, aiming for sites that are at least 50 ha in size and preferably larger than 100 ha. Each site should provide grasses of intermediate height and density and a well-developed litter layer. Although burning is necessary to control succession to woody vegetation, higher breeding densities were found on sites that had not been burned for at least 12 months. The Savannah Sparrow may require at least two years of litter accumulation until a site is suitable for nesting (Tester and Marshall 1961; Swanson  2002). As a result, only a portion of larger sites (25%–30%) should be burned in a given year. Light grazing on pastures is tolerated and helps to delay succession. Studies recommend leaving more than 40% cover of vegetation that is at least 25 cm in height (Swanson  2002).
Although it is an abundant and widely distributed species in Minnesota, the Savannah Sparrow’s precipitous population decline deserves attention. As conservation efforts in Minnesota continue to focus on the protection and restoration of grasslands, Savannah Sparrow populations should benefit. In particular, the cooperative interagency Prairie Conservation Program launched by the Minnesota Prairie Plan Working Group (2011) established aggressive goals for grassland and wetland conservation in the coming years. Such efforts should benefit an entire suite of grassland avifauna that is threatened by the loss of native grassland cover and by the uncertainty of a volatile commodities market, which affects the availability of planted grassland cover.
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