- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular breeding resident and migrant; birds are occasionally reported during the winter months. The Swamp Sparrow was an abundant species during the Minnesota Breeding Bird Atlas (MNBBA).
A northern species, the Swamp Sparrow’s breeding range stretches across much of Canada and the northern tier of the United States, from the eastern Great Plains and Minnesota, east across the Great Lakes and New England. The Swamp Sparrow reaches its highest breeding densities in Minnesota and Newfoundland (Figure 1).
Assigned a Continental Concern Score of 6/20 by Partners in Flight.
A short-distance migrant that winters in the southeastern United States and Mexico. Populations along the southern periphery of the species’ breeding range, in the southern Great Lakes and southern New England, are year-round residents.
An omnivorous ground forager and foliage gleaner that consumes invertebrates, seeds, and fruits.
Open-cup nest located just above the ground or water and supported by surrounding herbaceous or shrub vegetation; occasionally located on the ground.
In the late 1800s and early 1900s, Roberts (1932) considered the Swamp Sparrow a common breeding species across the state, although he noted that it was less frequently encountered in the western grasslands, particularly along the Red River valley. Commenting on its favorite haunts, he wrote:
The Swamp Sparrow, as its name implies, makes its home chiefly in the wetter portions of bogs and marshes where the cattails, rushes, and rank grasses flourish. Sluggish meadow streams, bordered by low willows and alders, are much to its liking. It is more secretive in its habits than the Song Sparrow and is loath to leave the concealment of its retreats.
At the time, confirmed nesting records (nests with eggs) were available from Hennepin, Jackson, Marshall, Otter Tail, and Sherburne Counties. Inferred nesting records (young out of the nest and adults carrying food) were available from Aitkin County and Itasca State Park.
Little had changed more than 40 years later when Green and Janssen (1975) prepared an updated account of the species’ status and commented that the Swamp Sparrow occurred statewide, wherever suitable wetland habitat was available. A few years later, Janssen (1987) identified 11 counties where nesting had been confirmed since 1970. All but 2, Goodhue and Le Sueur, were north of the Minnesota River valley. He noted that the species was particularly abundant in the “wooded swamps” of northern Minnesota, where 7 of the 11 records occurred. Five more counties were added by Hertzel and Janssen (1998), bringing the total list to 16. Thirteen of the 16 counties were located north of the Twin Cities; the remaining 3 were in southeastern Minnesota.
Field staff with the Minnesota Biological Survey documented 2,249 breeding season locations for the Swamp Sparrow. Observations were least numerous in the intensively cultivated regions of the Red River valley and the upper Minnesota River valley and in southeastern Minnesota (Minnesota Department of Natural Resources 2016).
MNBBA participants reported a total of 5,057 Swamp Sparrow records in 52.2% (2,489/4,772) of the surveyed atlas blocks and in 62.3% (1,457/2,337) of the priority blocks. Breeding evidence was documented in 152 blocks (Figures 2 and 3; Table 1). The birds were reported in all of Minnesota’s 87 counties and were confirmed breeding in 39 counties, 37 of which were located north of the Minnesota River (2 blocks straddled both Scott and Dakota Counties). Again, the species was virtually absent from the intensively cultivated Red River valley north of Wilkin County and was sparsely distributed in southeastern Minnesota. Based on MNBBA records, the Swamp Sparrow was the third most abundant sparrow in Minnesota, following the Song Sparrow and Chipping Sparrow.
Atlas data were used to develop a model to predict the relative abundance of Swamp Sparrows across Minnesota (Figure 4). This shrubby wetland–dependent species was predicted to have its highest probability of occurrence in the extensive wetland landscape of the Agassiz Lowlands Subsection and Tallgrass Aspen Parklands Province just north and west of Red Lake. Interestingly, as early as 1900, Roberts (1932) commented on how abundant the species was in this region. “Along the Moose River, in western Beltrami County, where the Swamp Sparrow was abundant in July, 1900, the writer heard it singing frequently during the midnight hours on bright moonlight nights.” Although there are small pockets of high abundance predicted throughout Minnesota, this expansive, largely inaccessible landscape provides ideal habitat. Miles of flat, poorly drained lake deposits, relics of Glacial Lake Agassiz, are covered by bogs, swamps, and fens that provide the wet habitat and low vegetation that characterize most Swamp Sparrow habitats (Minnesota Department of Natural Resources 2003). Areas of lowest abundance correlate with high development, including the Twin Cities, Rochester, and St. Cloud.
Over the years, field biologists and birders have consistently commented on the broad distribution of the Swamp Sparrow across Minnesota. Yet, because it resides exclusively in wetland habitats, a more in-depth assessment of its distribution and abundance have been lacking. Data gathered by the MNBBA provide a more informed assessment of its relative abundance across key ecological regions and its dependence on an entire landscape of remote wetlands that are largely inaccessible.
In his comprehensive review of the species, Mowbray (1997) noted only two minor changes to the Swamp Sparrow’s breeding range. The first was an apparent expansion along the mid-Atlantic coast in the mid-1900s, from eastern Maryland north to the Hudson River; the second was the species’ extirpation from northeastern Missouri. Breeding bird atlases conducted in the northern Great Plains and Upper Midwest consistently confirmed the species’ widespread occurrence with only a few distributional changes. In Wisconsin, the state’s first atlas (1995–2000) revealed the species was far more abundant and widespread in northern Wisconsin than previous accounts had described (Cutright et al. 2006). In South Dakota the state’s first atlas (1988–1992) found Swamp Sparrows widely distributed through the eastern half of the state but restricted to the northeastern corner of the state during the second atlas (2009–2012) (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||152 (3.2%)||107 (4.6%)|
|Probable||945 (19.8%)||714 (30.6%)|
|Possible||1,388 (29.1%)||635 (27.2%)|
|Observed||4 (0.1%)||1 (0.0%)|
|Total||2,489 (52.2%)||1,457 (62.3%)|
Aptly named, the Swamp Sparrow resides in a wide variety of wetland habitats ranging from freshwater wetlands in the interior to brackish and saltwater tidal marshes along the Atlantic coast. In Minnesota, the species is found in a diversity of wetlands, including permanent and semipermanent wetlands dominated by cattails and bulrushes, bogs and fens dominated by sedges and low ericaceous shrubs, and shrub wetlands and riparian thickets dominated by alders and willows (Figure 5; Kaufman 1996; Mowbray 1997; Danz et al. 2007). The National Forest Bird (NFB) Monitoring Program on Wisconsin and Minnesota’s four national forests found riparian habitats, lowland shrubs, and open wetlands were the dominant habitat types selected in these northern forest landscapes (Niemi et al. 2016). Habitat data collected within 200 m of MNBBA point counts where Swamp Sparrows were detected demonstrated the species’ strong preference for shrub wetlands and marsh/wet meadow habitats (Figure 6).
Regardless of the diversity of habitats that Swamp Sparrows find suitable, all sites appear to share three primary features outlined in a study in New England: shallow, standing water; low, dense cover that is usually less than 1.5 m in height; and elevated song perches (Reinert and Golet 1979). Shallow, standing water appears to be particularly important for foraging. Swamp Sparrows frequently feed on the ground in or adjacent to wet areas where they can glean aquatic seeds and invertebrates. They actually have longer leg bones than other members in the genus, allowing them to wade efficiently in water (Mowbray 1997).
Data gathered by the federal Breeding Bird Survey (BBS) have generated a North American population estimate of 22 million breeding adults (Rosenberg et al. 2016). In 2013, Minnesota was reported to support about 4% of the North American population and 42% of the U.S. population (Partners in Flight Science Committee 2013). Applying that percentage to the current estimate generates a statewide population of approximately 880,000 adults. The statewide estimate generated using MNBBA data was considerably larger at 3.7 million adults (95% confidence interval of 3.2 -5.3 million).
BBS data clearly demonstrate that Minnesota supports the highest density of breeding Swamp Sparrows in the United States (Figure 1). Since 1967, observers in Minnesota have recorded an annual average of approximately 6 sparrows per BBS route; survey-wide the average is only 2 birds per route (Sauer et al. 2017). The species’ abundance in Minnesota is second only to Newfoundland and Labrador, where an average of 15 birds were detected per BBS route from 1980 to 2012 (Environment Canada 2014).
Local breeding densities are quite variable and range from a low of 1.6 birds per 40 ha in peatland habitat in eastern Canada to a high of 351 birds per 40 ha in a sedge meadow in Ontario (Mowbray 1997). On the Chippewa National Forest in north-central Minnesota, the NFB Monitoring Program recorded an average of 1.9 pairs per 40 ha, and on the Superior National Forest, an average of 0.8 pairs per 40 ha (Niemi et al. 2016). Swamp Sparrows were among the 20 most abundant birds in only 1 of the 17 habitats sampled on the Chippewa National Forest: mature black spruce–tamarack stands, where densities averaged 3.3 pairs per 40 ha. On the Superior National Forest, the species was not one of the 20 most abundant species in any habitat (Niemi et al. 2016). These extensive upland forested landscapes are not the species’ prime habitat in Minnesota. By contrast, in the Agassiz Lowlands Subsection, the predicted core of the species’ breeding range in Minnesota, Swamp Sparrows attained breeding densities of 23.1 pairs per 40 ha in lowland conifer stands that were recently harvested (Bednar et al. 2016). In shrub swamps in the Red Lake Peatland, breeding densities of 28 pairs per 40 ha were reported (Nevers et al. 1981).
Range-wide, the Swamp Sparrow has demonstrated a slow but steady, nonsignificant population increase on the BBS survey routes since 1966, averaging 0.93% per year (Sauer et al. 2017). From 1970 to 2014, biologists estimated the continental population has increased 66% (Rosenberg et al. 2016).
In Minnesota, BBS data demonstrate a significant long-term increase of 1.36% per year, but from 2005 to 2015, the population took a downward trend, declining an average of 1.77% per year (Figure 7). On both the Chippewa and Superior National Forests Swamp Sparrows have shown no statistically significant trend from 1995 to 2015, although data on the Chippewa suggest a small decline (Figure 8). Overall, most populations in the BBS region are stable to increasing, except in the Maritime provinces, Alberta, eastern Wisconsin, eastern South Dakota, and northeastern Nebraska (Figure 9).
Factors influencing population trends at the local and regional level are not well understood. Because the species is dependent on wetland habitats and usually nests just above the water surface, local rainfall patterns likely have a major influence on annual reproductive success (Mowbray 1997).
Broadly distributed, with a relatively large and stable population, the Swamp Sparrow is not a conservation priority at either the state or federal level. It has been assigned a low Continental Concern Score of 6/20 (Rosenberg et al. 2016).
Because the Swamp Sparrow is largely restricted to North America’s boreal forest, Partners in Flight originally designated the species a Stewardship Species for the biome in an effort to recognize the area’s importance to the species’ long-term sustainability (Rich et al. 2004). Approximately 79% of the species’ North American population is confined to the boreal forest. As remote as this region may seem, between 1990 and 2000 nearly 7 million acres in three Canadian provinces (Ontario, Manitoba, and Saskatchewan) were impacted by forest clearing, road building, and other infrastructure developments associated with industries involved in natural resource extraction (Stanojevic et al. 2006a, 2006b). The scale of these changes prompted the creation of the Boreal Songbird Initiative, a collaborative devoted to conserving the boreal forest biome while promoting sustainable development (www.borealbirds.org).
Loss of habitat is not the only threat faced by species like the Swamp Sparrow that depend on this critical ecosystem. Warming temperatures also are a concern. A recent analysis of nearly 600 North American birds by the National Audubon Society classified the Swamp Sparrow as a “climate threatened” species. Their models predicted the species could lose 69% of its current summer range by the year 2080, forcing the birds to find suitable habitat across the Arctic tundra (Langham et al. 2015; National Audubon Society 2016).
Given the significance of Minnesota to the national population, continued and expanded efforts to protect and restore wetland habitats will ensure the Swamp Sparrow remains a significant component of the state’s bird community, as well as of North America’s avifauna, for years to come.
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