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Acadian Flycatcher

Empidonax virescens
Overview
Minnesota Seasonal Status:

A regular breeding resident and migrant; the Acadian Flycatcher was a rare species during the Minnesota Breeding Bird Atlas (MNBBA).

North American Breeding Distribution and Relative Abundance:

A breeding resident of the eastern deciduous forest, the Acadian Flycatcher’s range extends from the eastern edge of the Great Plains to the Atlantic Coast. It stretches as far north as southern Minnesota and east across the lower Great Lakes states to southern New England. To the south it is found from central Texas east along the Gulf Coast to northern Florida. It is sparsely distributed throughout its breeding range but reaches its highest breeding densities along the northern Atlantic Coast states of Virginia and North Carolina west through the Appalachians and south to Mississippi and Alabama (Figure 1).

Conservation Concern:
Conservation Status Score 11

Assigned a Continental Concern score of 11/20 by Partners in Flight; officially listed as a Minnesota Special Concern Species and designated a Species of Greatest Conservation Need by the Minnesota Department of Natural Resources.

Life History
Migration:

A long-distance, Neotropical migrant that winters in southern Central America and northern South America.

Food:

An aerial insectivore that hawks and gleans insects.

Nest:

A cup nest usually located in deciduous trees and shrubs.

Acadian Flycatcher Acadian Flycatcher. Empidonax virescens
© Don Faulkner
Figure 1.

Breeding distribution and relative abundance of the Acadian Flycatcher in North America based on the federal Breeding Bird Survey from 2011 to 2015 (Sauer et al. 2017).

Minnesota Breeding Bird Distribution*

The first official account of Minnesota birds by Dr. P.L. Hatch in 1892 included the Acadian Flycatcher and described it as “fairly common.” Although Hatch noted the frequent confusion of the species with the very similar Trail’s Flycatcher (now split into the Alder and Willow Flycatchers), which “put me on my guard,” he was quite certain of his observations. He also accepted additional reports of the species from the Root River in southeastern Minnesota and from the Red River valley in northwestern Minnesota.

Forty years later, Roberts (1932) summarily dismissed Hatch’s account, writing that the “whole article is without foundation in fact.” Although Hatch’s report of birds in southeastern Minnesota was at least plausible, the observer, Dr. Hvoslef, later wrote Dr. Roberts stating that his own identification was in error (Roberts 1932). Indeed, Roberts himself, anticipating the flycatcher would eventually appear in the state, spent many years searching for and collecting specimens of small Empidonax flycatchers but failed to document the occurrence of the Acadian Flycatcher. When Green and Janssen wrote their updated status account in 1975, they noted a report of singing flycatchers along the Root River, approximately 2.5 miles east of the town of Rushford, in 1940, but little else is known about the record.

Another 27 years would pass before the Acadian Flycatcher was unquestionably documented in Minnesota. During the summer of 1967, Fred Lesher discovered a nesting pair in Beaver Creek Valley State Park in Houston County (Lesher 1968). A regular breeding species at this park since Lesher’s discovery, Janssen (1987) provided a detailed account of its gradual expansion further north to Rice, Hennepin, and Chisago Counties and west to Fillmore County. Nesting was confirmed in Houston, Goodhue (Janssen 1974), Scott (Fall 1987), and Rice Counties (Green 1981). By 1998, breeding was confirmed in an additional four counties: Dakota, Hennepin, Ramsey, and Winona (Hertzel and Janssen 1998).

Beginning in the late 1980s, field biologists working with the Minnesota Biological Survey (MBS) documented a total of 54 breeding season observation locations for the species. The majority of records were found in the Eastern Broadleaf Forest Province from Morrison County south to Houston County and west along the Minnesota River valley to Nicollet County. A few records were reported as far north as Douglas County in west-central Minnesota and as far west as Lyon County and the border of Lincoln and Yellow Medicine Counties in the southwestern corner of the state (Minnesota Department of Natural Resources 2016a). Field work conducted by MBS staff in the summer of 1993 in Houston and Winona Counties provided an indication of the species’ rarity. Flycatchers were documented in only 8 of 38 forest stands that were considered suitable habitat (Minnesota Department of Natural Resources 1995).

In addition to the MBS records, since 1990 active birders have documented breeding season observations as far north as Aitkin County (2005) and as far west as Clay (1992) and Swift (1994) Counties (Minnesota Ornithologists’ Union 2016).

During the MNBBA, observers reported 34 Acadian Flycatcher records from just 25 of the surveyed atlas blocks and 8 priority blocks. Breeding was confirmed in 4 blocks (Figures 2 and 3; Table 1). The birds were reported in 15 of Minnesota’s 87 counties (4 records straddled both Scott and Dakota Counties and 1 record straddled Brown and Nicollet Counties) and were confirmed breeding in 4 counties (Hennepin, Goodhue, and a record that straddled Scott and Dakota). The majority of reports were from east-central and southeastern Minnesota, with 3 records further west in Brown/Nicollet, Otter Tail, and Stearns Counties. The most remarkable report was from northern Kittson County on June 19, 2012. The record was from an outstanding field ornithologist, Karl Bardon, of the MBS. A male was singing and calling in an aspen grove while Karl was conducting a point count survey. Given the unusual nature of the record, an audio recording was made as well (per Steve Stucker, pers. comm., Minnesota Biological Survey).

The Acadian Flycatcher remains a very rare species in Minnesota, confined primarily to the far east-central and southeastern counties. It also seems fairly well established along the lower Minnesota River valley in Brown and Nicollet Counties. Three localities where the species has been consistently reported include Beaver Creek Valley State Park in Houston County, Murphy Hanrehan Regional Park Reserve in Scott and Dakota Counties, and Seven Mile Creek Park in Nicollet County. Reports beyond these locations are rare and inconsistent from year to year.

Coincident with the species’ appearance and range expansion in Minnesota, the Acadian Flycatcher has been expanding its breeding range throughout the northeastern United States since the 1960s and 1970s. Records from the late 1800s and early 1900s documented that it is reoccupying portions of its former breeding range. For example, the Acadian Flycatcher was known to breed in Massachusetts in 1888 but then disappeared until the 1960s. The species was present in southern New York in the early 1900s but then disappeared until the early 1970s (Whitehead and Taylor 2002). Although the reasons for the range contraction and subsequent expansion are unknown, biologists believe the initial loss in forest cover, followed by an increase in forest cover and forest age in the latter half of the twentieth century in New England may be responsible (Whitehead and Taylor 2002).

The Acadian Flycatcher was even documented in South Dakota between the years 1918 and 1922 (Whitehead and Taylor 2002). Recent atlas work in the state, however, has failed to document the species’ presence (Drilling et al. 2016). To the east, in Wisconsin, the state’s first breeding bird atlas documented the Acadian Flycatcher in 12 counties in the central region of the state where they had not previously been reported. The species’ range appears to have expanded to the north and northwest in the state since at least the 1990s (Cutright et al. 2006).

*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 Acadian Flycatcher in Minnesota based on the Breeding Bird Atlas (2009 – 2013).

Print Map
Figure 3.

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

Breeding statusBlocks (%)Priority Blocks (%)
Confirmed4 (0.1%)2 (0.1%)
Probable14 (0.3%)6 (0.3%)
Possible6 (0.1%)0 (0.0%)
Observed1 (0.0%)0 (0.0%)
Total25 (0.5%)8 (0.3%)
Table 1.

Summary statistics for the Acadian Flycatcher 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).

Breeding Habitat

The Acadian Flycatcher’s breeding habitat has been broadly characterized as large, mature forest tracts associated with water. In the southern portion of its range, the species is commonly found in large Bald Cypress swamps, but as it moves further north into the central and northern portion of its range, deciduous hardwood stands are more common habitats. The latter include a diversity of forest communities such as deep forest ravines, lowland hardwoods, and mesic uplands. A dense canopy and a well-developed understory are key features of nearly all sites (Whitehead and Taylor 2002; Rodewald et al. 2016; Klubertanz 2013).

In Wisconsin, the species occurs in three major landscapes: mesic woodlands located along ravines or stream gorges, drier oak forests located along glacial moraines dotted with small kettles and valleys, and in upland conifer plantations (Cutright et al. 2006). The description of the first two landscapes is similar to the habitats occupied by the Acadian Flycatcher in Minnesota. In the southeastern Driftless region, the species was frequently found along steep, streamside ravines (Figure 4), which typify one of its most regular breeding sites at Beaver Creek Valley State Park. Field biologists have noted most stream valleys occupied by Acadian Flycatchers are narrow and forested on both sides of the valley, from the bottom of the valley to the top of the slope (Minnesota Department of Natural Resources 2016b).

Further north, in east-central Minnesota, drier oak forests, with scattered wetlands, are more typical of occupied sites such as Murphy Hanrehan and Elm Creek Park Reserves (Fall 1987; Johnson 1994). The atlas observation in Otter Tail County occurred in Maplewood State Park, a transitional landscape dominated by upland forests of sugar maple, basswood, and oaks. Further west, the 1992 observation in Clay County was in a woodland grove along the Rice River (Backstrom 1992), and the Kittson County Biological Survey record (2012) was in a woodland grove embedded within an extensive wetland complex on the Caribou Wildlife Management Area.

Fall (1987) provided a detailed description of the breeding habitat at Murphy Hanrehan Park Reserve. The birds occupied a large (3 km2), continuous stand of red oak, white oak, bur oak, American elm, and aspen with a dense, closed canopy (90%). Small wetland ponds were scattered throughout and the understory, which was not particularly dense, had thickets of prickly ash, hazel, and blackberry.

Several studies have demonstrated the species’ dependence on large, unfragmented forest tracts; in general the abundance of flycatchers increases with an increase in tract size. In Wisconsin, Temple (1988) estimated that the minimum area requirement was 100 ha; further south, in the mid-Atlantic region, Robbins (1980) estimated the requirement to be a minimum of 32 to 50 ha. The species is particularly vulnerable to parasitism by the Brown-headed Cowbird and to nest predation in highly fragmented landscapes (Robinson et al. 1995; Whitehead and Taylor 2002).

On the other hand, a study in Illinois suggested that the flycatcher might not be as sensitive to habitat fragmentation as other studies have suggested, at least within narrow floodplain corridors. As long as the corridors were at least 80 meters in width, with natural edges created by other vegetative communities (i.e., not anthropomorphic edges), nest survival was relatively high (Chapa-Vargas and Robinson 2007). The authors pointed out that the Acadian Flycatcher is one of the only forest-nesting, Neotropical migrants that nest in narrow corridors.

Figure 4.

Typical breeding habitat of the Acadian Flycatcher in Minnesota (© Lee A. Pfannmuller).

Population Abundance

Using long-term monitoring data gathered by the federal Breeding Bird Survey (BBS), biologists have estimated the North American population of the Acadian Flycatcher at 5 million breeding adults (Rosenberg et al. 2016). Nearly a decade earlier, the statewide estimate for this rare species in Minnesota was estimated at approximately 300 adults (Rosenberg 2004).

Density estimates for the species are generally low. Even in the heart of its breeding range in the southeastern United States, local breeding densities were usually less than one breeding pair per hectare (Whitehead and Taylor 2002). Along BBS routes, the average number of birds per route per year across the entire BBS survey area was 2, and the average ranges from fewer than 1 bird per route per year in the northern regions of its breeding range to as high as 12 per route per year in West Virginia (Sauer et al. 2017).

Since 1966, the North American population of the Acadian Flycatcher has been relatively stable. Its numbers slowly declined in the latter half of the twentieth century, but they have stabilized and begun a slow increase since 2005 (Figure 5). Given the species’ rarity, it is not possible to predict its statewide population trend in Minnesota. Only one bird has ever been reported on a BBS route in Minnesota (in 1993; Pardieck et al. 2016). Regionally, Acadian Flycatcher populations vary considerably, which likely reflects local changes in suitable habitat conditions. Overall, biologists estimated the species’ populations have declined 10% since 1970 (Rosenberg et al. 2016).

Figure 5.

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

Conservation

Concerns regarding the relatively small area the Acadian Flycatcher occupies during the winter and its dependence on intact, mature forests year-round have led to a moderate Continental Concern Score of 11/20 by Partners in Flight (Rosenberg et al. 2016). The loss of mature forests in the tropics more than two decades ago prompted biologists to predict that the species would decline in the coming years (Rappole et al. 1983). In 2004 it was listed as a Species of Stewardship Priority in the Eastern Deciduous Forest Biome (Rich et al. 2004).

In Minnesota the flycatcher was added to the official state list of Species of Special Concern in 1996 in light of its rarity and its dependence on large blocks of mature forest (Minnesota Department of Natural Resources 2016b). It is also designated a Species in Greatest Conservation Need by the Minnesota Department of Natural Resources (2015).

The future of the Acadian Flycatcher is clearly tied to the protection and management of mature deciduous forests on both the wintering and breeding grounds. Warming temperatures and their impact on suitable habitat may also be a concern. Although the potential response of the species to climate change has not been intensively studied, a preliminary assessment in 2010 rated it as moderately vulnerable (North American Bird Conservation Initiative 2010).

Management recommendations focus primarily on identifying, protecting, and managing large, unfragmented tracts of mature deciduous forest. Whitehead and Taylor (2002) recommended that such sites should be at least 10,000 ha in size, with as little internal disturbance as possible.

The state and regional park systems in southern Minnesota provide key habitat for the Acadian Flycatcher. Further opportunities to protect and manage forested, dissected river valleys and large upland forest tracts are critical not only for the future of the Acadian Flycatcher but also for many other area-sensitive songbirds in the southern and southeastern regions of the state.

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