- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular breeding resident and migrant in southeastern Minnesota. The Louisiana Waterthrush was a rare species during the Minnesota Breeding Bird Atlas (MNBBA).
A species of the eastern deciduous forest, the Louisiana Waterthrush has a breeding range that is restricted to the eastern United States and southern Ontario. It breeds as far west as eastern Nebraska, Oklahoma, and Texas. It reaches the northwestern periphery of its breeding range along the small tributaries and major river valleys of the Mississippi, Minnesota, and St. Croix Rivers in Minnesota. The species is sparsely distributed throughout its breeding range; the majority of birds breed in the Appalachian Mountain region (Figure 1).
Assigned a Continental Concern Score of 12/20 by Partners in Flight; officially classified as a Special Concern Species in Minnesota and designated a Species in Greatest Conservation Need by the Minnesota Department of Natural Resources.
A medium- to long-distance migrant that winters in the Caribbean and Central America.
Primarily aquatic invertebrates secured by probing along the steam edge or from atop exposed rocks. Also hawks and hovers to obtain flying insects or prey from foliage.
Open-cup nest nestled in the roots of an upturned tree, within a stream bank, or underneath a downed tree.
Roberts (1932) provided an account of the Louisiana Waterthrush’s northward expansion into Minnesota beginning with the first state record in 1883 along the Root River in Fillmore County. By 1893 it was reported common in that area, and by 1898 it was found as far north as Red Wing in Goodhue County. Just four years later, in 1903, an adult male was taken in Hennepin County near Minnehaha Falls. When Roberts wrote his account of the species two decades later, the Louisiana Waterthrush had become a regular, but uncommon breeding species in the Twin Cities region.
Once the species reached the mouth of the St. Croix River, it continued to expand north, and “hundreds” were reported along the river valley as far north as Taylors Falls in the summer of 1908. When Surber visited southern Pine County a decade later, during the summers of 1918 and 1919, he reported Northern Waterthrushes as rare along Crooked Creek, Sand Creek, and at the mouth of the Tamarack River, all tributaries of the St. Croix River. Roberts, however, assigned Surber’s observations to the Louisiana Waterthrush (Green and Janssen 1975). Today it is known that both species occur in Pine County, so both Surber and Roberts may have been correct. The species also followed the Minnesota River to the west, occurring as far as eastern Carver County. Although it was definitely expanding its range, Roberts commented that it was “still most numerous in the Mississippi River bottom-lands south of Red Wing, Goodhue County, and along the St. Croix River as far north as Pine County.” At the time, confirmed or inferred nesting records were confined to Carver, Hennepin, Houston, and Washington Counties.
Following Roberts’s accounts in the early 20th century, there were few reports of Louisiana Waterthrushes outside of the traditional locations in southeastern Minnesota and along the St. Croix River. Indeed, a large number of reports came from just two localities: Beaver Creek Valley State Park in Houston County, and near the small town of Franconia in Chisago County (Langley [Longley] 1973; Minnesota Ornithologists’ Union 2016). New summer reports were rare but began to document the species’ range extension farther north along the Mississippi River in Stearns County (Eckert 1970), and farther west along the Minnesota River in Blue Earth, Nicollet, Scott, and Sibley Counties (Minnesota Ornithologists’ Union 2016). By 1975 Green and Janssen had added inferred and confirmed breeding records in Chisago, Stearns, and Winona Counties to the 4 counties already identified by Roberts (1932).
Roberts’s decision to reassign Surber’s early Northern Waterthrush records in Pine County to the Louisiana Waterthrush was reaffirmed by multiple observations in the county in the early 1980s, including breeding confirmation in 1983 (Zumeta and Cincotta 1983). By 1987, Janssen’s updated account noted the birds were local residents not only along the Mississippi and St. Croix River valleys but also “up the Minnesota River Valley as far as Blue Earth County.” He included a distribution map that identified 5 counties where nesting had been confirmed since 1970: Chisago, Pine, Houston, Olmsted, and Winona. Hertzel and Janssen (1998) later added Fillmore and Washington Counties to the list.
In subsequent years, migrants were reported as far north as Clay County (O’Connor 2005), Red Lake County (Janssen 1988), and Kittson County (Bolduc 1989; Svingen 1996). But each report was of a single bird reported in May or during the fall migration. To date, nesting has never been confirmed north of Pine County.
Meanwhile, field biologists working with the Minnesota Biological Survey since the late 1980s reported a total of 83 breeding season locations for the Louisiana Waterthrush. Most records were restricted to the species’ primary range in southeast and east-central Minnesota; only 2 records stretched as far west as Nicollet and Blue Earth Counties and as far north as Pine County (Minnesota Department of Natural Resources 2016).
During the MNBBA, participants reported Louisiana Waterthrush detections in only 10 of the surveyed atlas blocks and in just 4 of the priority blocks (Figures 2 and 3; Table 1). Breeding was confirmed in only 1 block. The birds were reported from 10 of Minnesota’s 87 counties and were confirmed breeding in only 1 county, Washington. The farthest west they were reported was in the Minnesota River valley in a block that straddled northern Brown and western Nicollet Counties.
When Roberts wrote his comprehensive account of the Louisiana Waterthrush’s arrival to Minnesota in 1932, he predicted that the species would continue its westward expansion, as so many other avian immigrants from the south, such as the Red-bellied Woodpecker and Blue-gray Gnatcatcher, had done during the same time period. Although the Brown County/Nicollet County MNBBA record represents an extension of the species’ range by nearly 140 river miles west of where it was found in Carver County in 1928, there have been no other significant changes to the species’ range in Minnesota since the middle of the 20th century. Elsewhere, however, populations were expanding north, in New England, including in New York, Vermont, and Connecticut, and in Michigan, in the latter half of the 20th century. Biologists speculated that these movements may have been in response to new habitat opportunities made available by maturation of forests in areas that had been logged in the late 19th and early 20th centuries (Mattsson et al. 2009).
*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||1 (0.0%)||0 (0.0%)|
|Probable||3 (0.1%)||0 (0.0%)|
|Possible||6 (0.1%)||4 (0.2%)|
|Observed||0 (0.0%)||0 (0.0%)|
|Total||10 (0.2%)||4 (0.2%)|
Throughout its breeding range, the Louisiana Waterthrush is closely associated with clear, cold-water streams flowing through mature, mesic hardwood or mixed deciduous-coniferous forests (Figure 4). It generally prefers medium- to high-gradient, first- to third-order streams that provide healthy communities of aquatic invertebrates, the waterthrush’s primary food source. Although birds are frequently found in narrow, steep-sided ravines, they occasionally are found in wider floodplain forests, particularly in the northeastern United States (Mattsson et al. 2009; Dunn and Garrett 1997).
Habitats utilized by Louisiana Waterthrushes in Minnesota closely mirror those described from the heart of its breeding range farther south and east. The majority of reports are from cold-water creeks or small rivers, often in steeply sloped ravines with fast-flowing water (Eliason and Fall 1989; Stucker and Cuthbert 2000; Schumacher 1995; Surdick 1995). Many breeding territories along the St. Croix River are located near the mouths of smaller tributaries, but the birds have been reported also on steep, rocky slopes at the river’s edge and far from any nearby tributary (Eliason and Fall 1989). Several breeding season observations in Washington County and southern Pine County were along creeks flowing through broad floodplain forests where the only relief was provided by a low-rising stream bank (Zumeta and Cincotta 1983; Eliason and Fall 1989).
An important feature at the microhabitat level is the availability of exposed rocks within the streambed. Located at the edge of the stream or within a pool, these surfaces provide foraging perches that enable easier access to aquatic insects within the stream. Surdick (1995) demonstrated that occupied territories had at least six times more exposed rock surfaces than riparian sites where waterthrushes were absent. Not only are the rocks an important source of invertebrates, they also trap vegetative debris and its associated fauna from the stream’s current.
Little is known about the Louisiana Waterthrush’s area sensitivity, but some have suggested that the species benefits from a management approach that focuses on providing maximum forest cover in tracts that are at least 100 ha in size (Potter et al. 2007; Wilson 2008; Rosenberg et al. 1999). Forest edges and openings negatively impact the reproductive success of the waterthrush, which is highly susceptible to nest parasitism by Brown-headed Cowbirds (Stucker and Cuthbert 2000). Other important features include the availability of rocky crevices, hollows in upturned root clumps, and crannies within an earthen bank where the birds can build their nest.
The presence of Louisiana Waterthrushes along stretches of the St. Croix River that experience significant recreational activity during the summer months suggest that they can tolerate moderate levels of human disturbance (Eliason and Fall 1995). They do not, however, tolerate significant disturbance to the riparian forest, including grazing, logging, and development activities that open up the understory and canopy (Surdick 1995).
Data gathered by the federal Breeding Bird Survey (BBS) have been used to generate abundance models that result in an estimate of only 500,000 Louisiana Waterthrushes in North America (Rosenberg et al. 2016). Unfortunately, because the species is so rare in Minnesota and occurs in habitats rarely encountered along Minnesota’s roadside surveys, it has never been detected on a BBS route in the state since the survey began in Minnesota in 1967 (Sauer et al. 2017). As a result, a statewide population estimate is not available.
Rare in Minnesota, the Louisiana Waterthrush is not an abundant species anywhere within its breeding range (Figure 1). With one exception, the average number of birds detected per BBS route in 30 states within its breeding range is less than 1. The only exception is West Virginia, where the number of waterthrushes detected per route averages 1 to 2 birds (Sauer et al. 2017). In regions where suitable habitat is available, field studies have identified breeding densities that range from a low of 1.0 pairs per km of stream in Illinois (Robinson 1990) to a high of 2.8 pairs per km in Connecticut (Craig 1981).
Because the species is not well surveyed by the BBS monitoring program, most statistical analyses of statewide population trends lack precision. The only exception is West Virginia, where BBS data reveal a significant downward trend averaging 0.93% per year from 1966 to 2015. Survey-wide, BBS data also are statistically unreliable but depict a slow and significant population increase averaging 0.60% per year and increasing to 1.67% per year from 2005 to 2015. Biologists estimate that the population has increased by 34% from 1970 to 2014 (Rosenberg et al. 2016).
Most accounts of the Louisiana Waterthrush cite numerous factors that could negatively affect breeding populations, from forest management, habitat fragmentation, and residential development to acid rain and water-quality degradation. Few accounts identify factors that could be responsible for a population increase. Mattsson and his colleagues noted, however, that the core of the species’ breeding range occurs in the Appalachian Mountain region that extends from southeast New York to northern Alabama. Intensive forest clearing in the region in the early 20th century has ceased, and reforestation in some areas now may be responsible for small population increases (Mattsson et al. 2009).
Given its overall rarity and its dependence on mature riparian habitats and good water quality, the Louisiana Waterthrush has received a considerable amount of recognition by state and federal resource agencies. It has been assigned a Continental Concern Score of 12/20 by Partners in Flight (Rosenberg et al. 2016) and is designated as a focal species by the Upper Mississippi River & Great Lakes Region Joint Venture (Potter et al. 2007), which includes eastern Minnesota. In Minnesota the Louisiana Waterthrush has been officially classified as a Special Concern Species since 1984 (Coffin and Pfannmuller 1988) and has been designated a Species in Greatest Conservation Need by the Minnesota Department of Natural Resources (2015).
An in-depth field study of Louisiana Waterthrushes in southeastern Minnesota in 1997 and 1998 closely examined nesting requirements and the impact of habitat improvement projects for trout streams on features critical to the species’ survival (Stucker and Cuthbert 2000). Key to maintaining a sustainable population in this region of the state is the protection of contiguous, mature riparian forests adjacent to third-order, cold-water streams. The authors concluded that any activity that decreases the integrity of either the forest or the stream threatens to impact Louisiana Waterthrushes.
Two particularly important features of the species’ habitat are contiguous forest cover and the availability of suitable nesting sites. Activities that fragment the forest canopy and create forest openings, including forest management, residential development, and trout stream habitat improvement projects, can increase rates of nest parasitism by Brown-headed Cowbirds (Stucker and Cuthbert 2000). Other studies have recommended that riparian forest buffers should be at least 100 m wide on both sides of the stream and mature enough to provide shade to the stream (Potter et al. 2007).
Equally critical is the protection of stream banks that provide nesting habitat. Most waterthrushes in southeastern Minnesota placed their nests along an eroded, steep stream bank that was relatively free of vegetation, a habitat created by natural fluvial processes within the stream corridor. Habitat improvement projects designed to stabilize these stream banks, especially along riparian corridors in mesic forest cover, degrade the habitat for waterthrushes (Stucker and Cuthbert 2000).
Warming temperatures also can threaten species like the Louisiana Waterthrush that depend on cool mesic forests and cold-water streams. The 2010 “State of the Birds” report assessed the species’ vulnerability to climate change as moderate (North American Bird Conservation Initiative 2010). A more recent analysis by the National Audubon Society classified the waterthrush as a “climate threatened” species and predicted the species could lose 97% of its current summer breeding range by the year 2080 (Langham et al. 2015; National Audubon Society 2016).
For a species that is already quite uncommon, another hazard is its vulnerability to mortality at communication towers. The estimated annual mortality is approximately 3,600 birds, or 1.4% of the population (Longcore et al. 2013).
Clearly, if the Louisiana Waterthrush is to remain a member of Minnesota’s avifauna, concerted management efforts are needed to provide suitable habitat and to help mitigate losses due to other threats. Timber management efforts on county, state, and federal lands that focus on protecting riparian forests have been actively promoted and implemented in Minnesota and are critical to the species’ future. Equally important, however, are efforts to retain the integrity of the stream environment.
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