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Grasshopper Sparrow

Ammodramus savannarum
Overview
Minnesota Seasonal Status:

A regular breeding resident and migrant; the Grasshopper Sparrow was an uncommon species during the Minnesota Breeding Bird Atlas (MNBBA).

North American Breeding Distribution and Relative Abundance:

Found primarily from the Great Plains south to southern Texas and east to the Atlantic coast, from southern Maine south to northern Georgia. Populations are found in the very southern regions of the Canadian Prairie Provinces and in southwestern Ontario and southern Quebec. Farther west, local populations are found in the northwestern United States and in California. The Grasshopper Sparrow attains its highest breeding densities in the Great Plains from North Dakota south through Nebraska (Figure 1).

Conservation Concern:
Conservation Status Score 12

Assigned a Continental Concern Score of 12/20 and designated a Common Bird in Steep Decline by Partners in Flight; designated a Species in Greatest Conservation Need by the Minnesota Department of Natural Resources and a Target Conservation Species by Audubon Minnesota.

Life History
Migration:

A short- to medium-distance migrant that winters in the southern United States and Central America; populations along the southern periphery of the breeding range are year-round residents..

Food:

An omnivorous ground forager that feeds on insects, especially grasshoppers, and seeds.

Nest:

An open-cup nest that often has a partial dome; placed on the ground at the base of a clump of grasses or forbs.

Grasshopper Sparrow Grasshopper Sparrow. Ammodramus savannarum
© Sparky Stensaas
Figure 1.

Breeding distribution and relative abundance of the Grasshopper Sparrow in North America based on the federal Breeding Bird Survey, 2011–2015 (Sauer et al. 2017).

Minnesota Breeding Bird Distribution*

Located on the northern periphery of its breeding range in Minnesota, the Grasshopper Sparrow is an inconspicuous and secretive bird with a faint, insect-like trill for a song. Roberts (1932) described the species as a breeding resident throughout the state. Most abundant on the western prairies, it even extended, albeit sparingly, into the northern forests “wherever there are extensive clearings and sparsely wooded areas.” Roberts provided several examples of its northern habitats, including records from the counties of St. Louis (Lake Vermilion), Lake (Two Harbors), Pine, Hubbard, and southern Beltrami. Confirmed nesting records (nests with eggs or young) were limited to western and east-central Minnesota and included Hennepin, Jackson, Polk, Sherburne, and Wilkin Counties. An inferred breeding record (large young) was reported from Ramsey County.

The species garnered little attention over the years from biologists and birders alike. Even Roberts’s account in 1932 was one of the shortest accounts he prepared for his two-volume treatise for such a common and widespread species. Only two, very short notes have been published in the state ornithological journal, The Loon, since its inception in 1929 through 2017.

Green and Janssen’s (1975) updated account of the species also described it as a statewide resident during the breeding season. Although there were summer records from as far north as Cook, northern St. Louis, Lake of the Woods, and Roseau Counties, it was rare in the northeast and north-central regions of the state. Several years later, Janssen (1987) suggested the species might be spreading north into Roseau and Kittson Counties “where suitable open grassy habitat exists.” Despite its rather broad distribution, nests were particularly difficult to locate. Janssen identified only 7 counties where nesting was confirmed since 1970: Brown, Clay, Cottonwood, Norman, Ramsey, Rock, and Wabasha. By 1998 Hertzel and Janssen added another 4 counties to the list: Aitkin, Kandiyohi, Sherburne, and Stevens.

Field biologists with the Minnesota Biological Survey (MBS) have documented 529 breeding season locations since their field surveys began in the late 1980s. The overwhelming majority of records are outside of the Laurentian Mixed Forest Province; the few reports within this region are confined largely to the western and southern borders of the province. In northwestern Minnesota, records were found as far north as Marshall, Kittson, and Roseau Counties (Minnesota Department of Natural Resources 2016).

MNBBA participants reported 761 Grasshopper Sparrow records from 9.8% (463/4,747) of the surveyed atlas blocks and from 11.9% (277/2,337) of the priority blocks. Breeding evidence was gathered in 25 blocks (Figures 2 and 3; Table 1). The birds were reported from 78 of Minnesota’s 87 counties, and breeding was confirmed in 22 counties, including at a site in St. Louis County (1 block straddled 2 counties: Lac qui Parle and Chippewa). The latter report was from a reclaimed taconite tailings basin along the Iron Range. Seventeen of the counties where breeding evidence was gathered were new to the list published by Hertzel and Janssen in 1998. The majority of atlas reports were from the Prairie Parkland and Eastern Broadleaf Forest Provinces. Compared to data compiled by the MBS, the atlas documented more reports from the Tallgrass Aspen Parklands Province and more reports farther east into the Laurentian Mixed Forest Province.

During the atlas period, birders also reported confirmed nesting records in 3 additional counties: (1) a summer 2010 report of adults carrying food in Crow-Hassan Park Reserve in Hennepin County; (2) a summer 2011 report of adults carrying food in Grey Cloud Dunes Scientific and Natural Area in Washington County; and (3) a summer 2012 report of fledged young in Faribault County (Minnesota Ornithologists’ Union 2016). Locational information was not detailed enough to ascribe these records to specific atlas blocks.

Atlas data were used to generate a model to predict the probability of encountering the species across the state (Figure 4). The result accurately depicts the sparse distribution of the species throughout all but the most densely forested regions of northeastern and north-central Minnesota where it is rare to absent. It also predicts that the Tallgrass Aspen Parklands Province and the Prairie Coteau of southwestern Minnesota support the highest breeding densities in the state. Elliot (2016) developed a similar predictive model for the Grasshopper Sparrow in southwestern Minnesota. The result is quite similar to that depicted by MNBBA data in Figure 4 in the southwest region.

Overall, the Grasshopper Sparrow’s distribution appears to have changed very little in the past 100 years in Minnesota. Forest clearing has likely provided more habitat opportunities for the species in the western and southern regions of the Laurentian Mixed Forest Province, but it still remains a sparsely distributed species there and elsewhere throughout the state.

Loss of grassland habitat throughout the sparrow’s breeding range has led to major population declines. In many eastern regions the species is present only in small remnant populations (Vickery 1996). In Wisconsin the species is locally distributed throughout the southern two-thirds of the state; their first atlas confirmed its “spotty and local distribution” (Cutright et al. 2006). Neither Iowa nor South Dakota, states that have completed two atlases (Drilling 2011; Iowa Ornithologist’ Union 2017), documented major changes in the species’ distribution or abundance between the two atlas efforts, despite significant declines in abundance in both states documented by the federal Breeding Bird Survey (BBS) (Sauer et al. 2017).

*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.

Figure 2.

Breeding distribution of the Grasshopper Sparrow in Minnesota based on the Breeding Bird Atlas (2009 – 2013).

Print Map
Figure 3.

Summary statistics of observations by breeding status category for the Grasshopper Sparrow in Minnesota based on all blocks (each 5 km x 5 km) surveyed during the Breeding Bird Atlas (2009-2013).

Breeding statusBlocks (%)Priority Blocks (%)
Confirmed26 (0.5%)10 (0.4%)
Probable121 (2.5%)78 (3.3%)
Possible314 (6.6%)187 (8.0%)
Observed3 (0.1%)2 (0.1%)
Total464 (9.8%)277 (11.9%)
Table 1.

Summary statistics for the Grasshopper Sparrow observations by breeding status category for all blocks and priority blocks (each 5 km x 5 km) surveyed during the Minnesota Breeding Bird Atlas (2009-2013).

Figure 4.

Predicted breeding distribution (pairs per 40 hectares) of the Grasshopper Sparrow in Minnesota based on habitat, landscape context, and climate data gathered during the Minnesota Breeding Bird Atlas (2009-2013) using the General Linear Modeling method with an adjustment for detectability.

Breeding Habitat

An obligate grassland species, the Grasshopper Sparrow was originally dependent on North America’s expansive native prairie biome. But the extensive clearing of forests that followed European settlement enabled the species to expand its range as it came to utilize pastures, old fields, and, to a much limited extent, croplands such as small grain fields (Bent 1968). More recently the species has made use of restored grasslands on capped landfills and reclaimed surface mines as well as planted cover provided by land retirement programs such as the Conservation Reserve Program (CRP) (Hanowski 1995; Vickery 1996; Dechant et al. 2002).  In the Upper Midwest, large tracts of mesic to dry grasslands, pastures, and old fields are most commonly used (Figure 5). In the more arid region of its breeding range, in the southern and western United States, it is associated with denser, shrubbier vegetation than in the Upper Midwest and East, where sparser vegetation is preferred (Vickery 1996; Sample and Hoffman 1989; Ruth 2015).  Habitat data collected within 200 m of MNBBA point counts where the species was detected demonstrate its strong preference for upland grasslands (Figure 6).

At the local scale a number of structural habitat features are important predictors of a site’s suitability for Grasshopper Sparrows. Primary features are grassland tracts with short vegetation and areas of bare ground, which may enable more efficient foraging opportunities, and clumps of tall, stiff-stemmed vegetation, which are important song perches (Whitmore 1981; Dechant et al. 2002; Elliot 2016). Studies in Wisconsin and Minnesota documented that sites with 8% to 9% bare ground are ideal (Sample and Mossman 1997; Elliot 2016). Although some studies suggest that shrub cover is important to the species, particularly in the southwestern and western United States (Bock and Bock 1987, 1992), studies in the Upper Midwest suggest they prefer sites with only 3% to 4% cover. When shrub cover increases above this level, nesting densities of sparrows decline (Sample and Mossman 1997; Elliot 2016). Densities also decreased as vegetation height exceeded about 45 cm (Elliot 2016). Dense vegetation may be tolerated if it is patchy in distribution (Sample and Mossman 1997). Tree cover is avoided.

Although many studies have concluded that the Grasshopper Sparrow is an area-sensitive species (e.g., Herkert 1994; Vickery et al. 1994), others have questioned that conclusion. Ribic and her colleagues (2009) identified 10 studies that showed a positive relationship between the species’ occurrence and/or breeding density with patch size, and only 1 study that showed a variable relationship. Johnson (2001), critical of the interpretation and sampling of a number of field studies, identified 3 studies that adequately addressed these concerns and demonstrated the species’ area sensitivity. His own study, on CRP lands in North Dakota, showed a variable response: in some local landscapes the birds demonstrated sensitivity to patch size, and in others they did not (Johnson and Igl 2001). Despite this variable response, Johnson and Igl concluded that establishing larger, contiguous grasslands that include a matrix of native and restored grasslands is far preferable than establishing small, fragmented sites some distance from one another.

In Minnesota, several studies have examined this issue and have concluded the species fares better on larger tracts. Johnson and Temple (1990) concluded that nest success was higher on larger tracts (130–486 ha) than on smaller tracts (16–32 ha). Success was also higher when nests were located farther from a woodland edge (>45 m). This study, however, was among those whose results Johnson (2001) questioned. Two recent studies in the state also demonstrated that breeding densities increased as the amount of grassland increased (Dunlap 2013; Elliot 2016). Elliot (2016), conducting an in-depth study of Grasshopper Sparrows in southwestern Minnesota, showed that features at both the local scale and landscape scale were critical in predicting the species’ occurrence and relative abundance. In the absence of detailed habitat data at the local scale, their presence can be approximated simply by knowing the amount of grassland present within 800 m of any site within the landscape.

Figure 5.

Typical breeding habitat of the Grasshopper Sparrow in Minnesota (© Lee A. Pfannmuller).

Figure 6.

Habitat profile for the Grasshopper Sparrow based on habitats within 200 m of point counts where the species was present during the Minnesota Breeding Bird Atlas (2009-2013).

Population Abundance

BBS data have been used to generate a North American population estimate of 31 million breeding adults (Rosenberg et al. 2016) The statewide estimate for Minnesota is 300,000 birds, or 0.80% of the global estimate (Partners in Flight Science Committee 2013). Statewide estimates using MNBBA data were extremely variable. Although they generated a median estimate of 948,000 breeding adults, the wide confidence interval suggests a low reliability in the projected number of this inconspicuous little grassland sparrow.

Located east of the core of the species’ range, Minnesota has breeding densities of Grasshopper Sparrows that are relatively low compared with numbers found in the northern and central Great Plains states farther west (Figure 1). The gradient in abundance is quite steep. Over the past 50 years, an average of 3 sparrows are detected each year per BBS route in Minnesota; in North Dakota an average of 35 birds have been reported, and in South Dakota an average of 68 birds (Sauer et al. 2017). Because these are 50-year averages and the species has been steadily declining, these data overestimate current abundance. In the year 2015 the average number of birds per route in Minnesota was less than 1; in North Dakota and South Dakota it was 13 and 18, respectively (Pardieck et al. 2016).

Breeding densities in field studies are quite variable. Studies in North Dakota between 1967 and 1993 showed a range of 0 to 8 pairs per 40 ha in habitats ranging from cropland with the lowest densities to planted cover with the highest densities (Igl et al. 2006). A study of CRP lands in west-central Minnesota documented an average of 4 pairs per 40 ha (Hanowski 1995). Recent work in southwestern Minnesota by Elliot (2016) documented 6 birds per 40 ha.

The most concerning aspect of the Grasshopper Sparrow’s population is its steady and significant decline. Since 1966, the species has experienced a significant annual decline of 2.52% per year throughout North America; the decline has slowed substantially to only 0.77% per year from 2005 to 2015 (Sauer et al. 2017). From 1970 to 2014, the decline represented a cumulative loss of 68% (Rosenberg et al. 2016). As steep as this decline is, it is even more dramatic in Minnesota, where the species has declined at an average rate of 7.56% per year since 1967. Unlike the trend at the national level, the statewide trend has not abated in recent years, declining at the rate of 7.88% per year from 2005-2015 (Figure 7). The decline is widespread throughout the species’ breeding range (Figure 8).

Habitat loss and degradation are the most important factors responsible for the population decline in Minnesota and throughout the Grasshopper Sparrow’s breeding range. Not only has North America lost more than 50% of its native grasslands, those that remain are increasingly fragmented and subject to management and successional changes that reduce their suitability for an entire suite of grassland-dependent species. Recent field studies in the Chihuahuan Desert of northern Mexico, a critically important area for wintering Grassland Sparrows and 27 other grassland-dependent species from the northern Great Plains, have demonstrated that significant threats exist also on the wintering grounds. From 2006 to 2011, the conversion of grasslands to croplands occurred at a rate of 6.04% per year. Indeed, researchers predicted that at the present rate all grassland habitat in the Chihuahuan Desert would be converted to cropland as early as 2025 (Pool et al. 2014).

Figure 7.

Breeding population trend for the Grasshopper Sparrow in Minnesota for 1967–2015 based on the federal Breeding Bird Survey (Sauer et al. 2017).

Figure 8.

Breeding population trend map for the Grasshopper Sparrow in North America for 1966–2015 based on the federal Breeding Bird Survey (Sauer et al. 2017).

Conservation

The species’ dependence on grasslands and its significant population decline have garnered the attention of numerous conservation organizations and resource agencies at both the federal and state level. In their 2016 Landbird Conservation Plan, Partners in Flight designated the species as a Common Species in Steep Decline with a Continental Concern Score of 12/20 (Rosenberg et al. 2016).

In Minnesota the Grasshopper Sparrow has been designated a Species in Greatest Conservation Need (Minnesota Department of Natural Resources 2015). Audubon Minnesota also designated the Grasshopper Sparrow a Target Conservation Species and one of four species to represent the Prairie Parkland Province. The organization’s conservation plan for the species established a conservation goal that mirrors the North American plan (Pfannmuller 2014).

The challenges in protecting this species are many. Although the sparrow has adapted well to planted cover on nonnative grasslands, it is vulnerable to agricultural practices and farm policies that waiver in response to commodity prices and overseas markets. For example, high use of lands enrolled in the CRP can negatively impact populations when commodity prices are high and farmers are disinclined to enroll acres in set-aside programs. Even grasslands that are protected through acquisition or easement programs are vulnerable if funding is insufficient to insure proper management to halt encroachment by woody vegetation. Although the impacts of warming temperatures on the sparrow’s population have not been intensively examined, numerous studies have pointed out major impacts to grasslands in both the species’ breeding and wintering range resulting from climate change (Ruth 2015).  In the near term, however, the most important conservation tool is the protection and management of remaining grassland tracts.  In Minnesota, efforts advocated by the Minnesota Prairie Conservation Plan are an excellent example of the creative, interagency work that is needed to insure the survival of numerous grassland dependent species (Minnesota Prairie Plan Working Group 2011).

Increased interest in utilizing grasslands for the production of biofuels as an alternative energy source may actually provide another conservation tool for some grassland species that are more reliant on shorter vegetation. A study in western Minnesota concluded that harvesting grasslands for biofuel production had little impact on grassland songbirds. Indeed, the Grasshopper Sparrow was one of two species that actually increased in abundance with increasing harvest levels (Dunlap 2013). Grassland biofuels may not only be a viable alternative source of energy but may provide farmers with a cost-effective alternative when payments for CRP lands decline.

In the interim, the Grasshopper Sparrow’s habitat requirements are sufficiently well understood to provide resource managers with strong guidance for maintaining and improving habitat conditions. Similar to the requirements of many grassland birds, management efforts that embrace a diversity of prescriptions and practices (e.g., grazing, mowing, and burning) will provide a mosaic of cover conducive to an entire suite of grassland-dependent birds (Ruth 2015; Dechant et al. 2002).

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