Empidonax virescens - (Vieillot, 1818)
Acadian Flycatcher
Other English Common Names: Acadian flycatcher
Taxonomic Status: Accepted
Related ITIS Name(s): Empidonax virescens (Vieillot, 1818) (TSN 178339)
French Common Names: Moucherolle vert
Spanish Common Names: Mosquero Verdoso
Unique Identifier: ELEMENT_GLOBAL.2.103712
Element Code: ABPAE33020
Informal Taxonomy: Animals, Vertebrates - Birds - Perching Birds
 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Aves Passeriformes Tyrannidae Empidonax
Genus Size: C - Small genus (6-20 species)
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Concept Reference
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Concept Reference: American Ornithologists' Union (AOU). 1998. Check-list of North American birds. Seventh edition. American Ornithologists' Union, Washington, D.C. [as modified by subsequent supplements and corrections published in The Auk]. Also available online: http://www.aou.org/.
Concept Reference Code: B98AOU01NAUS
Name Used in Concept Reference: Empidonax virescens
Conservation Status
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NatureServe Status

Global Status: G5
Global Status Last Reviewed: 07Apr2016
Global Status Last Changed: 02Dec1996
Ranking Methodology Used: Ranked by inspection
Rounded Global Status: G5 - Secure
Nation: United States
National Status: N5B (19Mar1997)
Nation: Canada
National Status: N2N3B,NNRM (05Jan2018)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Alabama (S5B), Arkansas (S4B), Connecticut (S4B), Delaware (S5B), Florida (SNRB), Georgia (S5), Illinois (S5), Indiana (S4B), Iowa (S3B,S3N), Kansas (S3B), Kentucky (S5B), Louisiana (S5B), Maryland (S5B), Massachusetts (S2B), Michigan (S4), Minnesota (S3B), Mississippi (S5B), Missouri (SNRB), Nebraska (S2?), New Jersey (S4B), New York (S3B), North Carolina (S5B), Ohio (S5), Oklahoma (S4B), Pennsylvania (S5B), Rhode Island (S1B,S1N), South Carolina (S4B), South Dakota (SH), Tennessee (S5), Texas (S4S5B), Virginia (S5), West Virginia (S5B), Wisconsin (S3B)
Canada Ontario (S2S3B)

Other Statuses

Canadian Species at Risk Act (SARA) Schedule 1/Annexe 1 Status: E (05Jun2003)
Committee on the Status of Endangered Wildlife in Canada (COSEWIC): Endangered (25Apr2010)
Comments on COSEWIC: Reason for designation: In Canada, this species is restricted to certain types of mature forest in southern Ontario. Only small numbers breed in Canada. Although the population appears to have been relatively stable over the past 10-20 years, this is most likely due to immigration from U.S. populations. The species is threatened by forestry practices, particularly those that target removal of large trees. Serious conservation concerns, both in Canada and the adjacent U.S. also stem from increasingly widespread losses of a variety of favoured nest tree species owing to the spread of an array of exotic forest insects and pathogens. Collectively, these threats to habitat greatly reduce potential for rescue from adjacent U.S. populations.

Status history: Designated Endangered in April 1994. Status re-examined and confirmed in November 2000 and April 2010.

IUCN Red List Category: LC - Least concern

NatureServe Global Conservation Status Factors

Range Extent: >2,500,000 square km (greater than 1,000,000 square miles)
Range Extent Comments: BREEDING: southeastern South Dakota east across southern Great Lakes region to southern New England, south to southern Texas, Gulf Coast, and central Florida, west to central Kansas (AOU 1983); in Canada, restricted to southwestern Ontario. The highest nesting densities were in the Cumberland Plateau and in Virginia and West Virginia (Robbins et al. 1986). NON-BREEDING: Caribbean slope of Nicaragua, both slopes of Costa Rica and Panama, and in northern and western Colombia, northern Venezuela, and western Ecuador (AOU 1983).

Overall Threat Impact Comments: The primary threat to this species, as with other neotropical migrants, is habitat degradation and fragmentation (and therefore indirectly, cowbird parasitism and nest predation). Habitat loss and fragmentation due to conversion of natural forest to pine plantations, as well as residential development, strip mining, and road construction are also contributing to habitat loss in Alabama (Bailey, pers. comm.), Delaware (Heckscher, pers. comm.), Kansas (Busby, pers. comm.), and Mississippi (Mann, pers. comm.). Cowbird parasitism is cited as the primary threat in Illinois (Kleen, pers. comm.) and Kansas (Mann, pers. comm.). Flycatchers are impacted by the Brown-headed Cowbird (MOLOTHRUS ATER), although the general consensus seems to be that they are not as heavily parasitized upon by cowbirds as many other open-nesting forest species (Bent 1942, Walkinshaw 1961, 1966, Robinson 1992, Whitehead 1992). Nest predators also significantly impact this species and nest predation has the greatest effect on nest success.

Short-term Trend: Increase of >10%
Short-term Trend Comments: North American Breeding Bird Survey (BBS) data show a consistent increase survey-wide of 0.5% per year from 1966 to 1996, though this is not statistically significant (Sauer et al. 1997). Trends by state and physiographic stratum vary throughout the range, with some states (e.g. Maryland) showing significant increases and other states (e.g. Arkansas, Florida) showing significant decreases.

Other NatureServe Conservation Status Information

Distribution
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Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) BREEDING: southeastern South Dakota east across southern Great Lakes region to southern New England, south to southern Texas, Gulf Coast, and central Florida, west to central Kansas (AOU 1983); in Canada, restricted to southwestern Ontario. The highest nesting densities were in the Cumberland Plateau and in Virginia and West Virginia (Robbins et al. 1986). NON-BREEDING: Caribbean slope of Nicaragua, both slopes of Costa Rica and Panama, and in northern and western Colombia, northern Venezuela, and western Ecuador (AOU 1983).

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
NOTE: The maps for birds represent the breeding status by state and province. In some jurisdictions, the subnational statuses for common species have not been assessed and the status is shown as not-assessed (SNR). In some jurisdictions, the subnational status refers to the status as a non-breeder; these errors will be corrected in future versions of these maps. A species is not shown in a jurisdiction if it is not known to breed in the jurisdiction or if it occurs only accidentally or casually in the jurisdiction. Thus, the species may occur in a jurisdiction as a seasonal non-breeding resident or as a migratory transient but this will not be indicated on these maps. See other maps on this web site that depict the Western Hemisphere ranges of these species at all seasons of the year.
Endemism: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
United States AL, AR, CT, DE, FL, GA, IA, IL, IN, KS, KY, LA, MA, MD, MI, MN, MO, MS, NC, NE, NJ, NY, OH, OK, PA, RI, SC, SD, TN, TX, VA, WI, WV
Canada ON

Range Map
Note: Range depicted for New World only. The scale of the maps may cause narrow coastal ranges or ranges on small islands not to appear. Not all vagrant or small disjunct occurrences are depicted. For migratory birds, some individuals occur outside of the passage migrant range depicted. For information on how to obtain shapefiles of species ranges see our Species Mapping pages at www.natureserve.org/conservation-tools/data-maps-tools.

Range Map Compilers: NatureServe, 2002; NatureServe, 2005; WILDSPACETM 2002


U.S. Distribution by County Help
State County Name (FIPS Code)
CT Fairfield (09001)*, Litchfield (09005)*, Middlesex (09007), New Haven (09009)*, Tolland (09013)*, Windham (09015)*
MN Anoka (27003), Carver (27019), Chisago (27025)*, Dakota (27037), Douglas (27041), Fillmore (27045), Goodhue (27049), Hennepin (27053), Houston (27055), Kittson (27069), Le Sueur (27079), Lincoln (27081), Lyon (27083), Nicollet (27103), Olmsted (27109), Ramsey (27123), Rice (27131), Scott (27139), Stearns (27145), Wabasha (27157), Winona (27169), Wright (27171)
NE Nemaha (31127), Richardson (31147)
NJ Atlantic (34001), Cape May (34009), Cumberland (34011), Mercer (34021), Monmouth (34025), Sussex (34037)
RI Kent (44003), Newport (44005), Providence (44007)
WI Columbia (55021), Crawford (55023), Dane (55025), Dunn (55033), Fond Du Lac (55039), Grant (55043), Green (55045), Green Lake (55047), Iowa (55049), Jackson (55053), Jefferson (55055), Juneau (55057), La Crosse (55063), Lafayette (55065), Langlade (55067), Manitowoc (55071), Monroe (55081), Outagamie (55087), Ozaukee (55089), Richland (55103), Rock (55105), Sauk (55111), Sheboygan (55117), Vernon (55123), Walworth (55127), Washington (55131), Waukesha (55133)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
01 Lower Connecticut (01080205)+, Narragansett (01090004)+, Pawcatuck-Wood (01090005)+, Quinebaug (01100001)+, Shetucket (01100002)+*, Quinnipiac (01100004)+*, Housatonic (01100005)+*, Saugatuck (01100006)+*
02 Rondout (02020007)+, Hackensack-Passaic (02030103)+, Long Island Sound (02030203)+*, Middle Delaware-Musconetcong (02040105)+, Cohansey-Maurice (02040206)+, Great Egg Harbor (02040302)+
04 Manitowoc-Sheboygan (04030101)+, Upper Fox (04030201)+, Wolf (04030202)+, Milwaukee (04040003)+
07 Clearwater-Elk (07010203)+, Twin Cities (07010206)+, Lac Qui Parle (07020003)+, Chippewa (07020005)+, Redwood (07020006)+, Middle Minnesota (07020007)+, Lower Minnesota (07020012)+, Lower St. Croix (07030005)+, Rush-Vermillion (07040001)+, Cannon (07040002)+, Buffalo-Whitewater (07040003)+, Zumbro (07040004)+, La Crosse-Pine (07040006)+, Black (07040007)+, Root (07040008)+, Red Cedar (07050007)+, Coon-Yellow (07060001)+, Grant-Little Maquoketa (07060003)+, Castle Rock (07070003)+, Baraboo (07070004)+, Lower Wisconsin (07070005)+, Kickapoo (07070006)+, Upper Rock (07090001)+, Crawfish (07090002)+, Pecatonica (07090003)+, Sugar (07090004)+, Upper Fox (07120006)+
09 Roseau (09020314)+
10 Tarkio-Wolf (10240005)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A small bird (flycatcher).
General Description: Length 5.75 in (15 cm). Sexes similar. Olive above, with yellow eye ring, two buffy or whitish wing bars; very long primaries. Bill proportionately long and broad-based, with mostly yellowish lower mandible. Underparts vary; most birds show pale grayish throat, pale olive wash across upper breast, white lower breast, and yellow belly and undertail coverts. Worn late-summer birds show almost no yellow below. Molts before migration; fall birds have buffy wing bars. Juvenile is brownish-olive above, edged with buff; wing bars buffy; underparts whitish with olive wash on breast. The only Empidonax in the southeastern lowlands in summer (NGS 1987).

VOICE: Call is a loud but soft "peek", extended in song to an emphatic "peet-sah", usually accented on first syllable, but sometimes with equal accent on both syllables (Kaufman 1990). On breeding grounds, this species also gives a flicker-like "ti ti ti ti ti" (NGS 1987). Usually gives an impression of lethargy, doing very little flicking of the wings or tail except when excited. Often perches with the wings drooped somewhat (Kaufman 1990).

NEST: Frail, saucer-shaped, shallow basket swung hammocklike between horizontal twigs of a slender limb. Built of fine, dry plant stems, plant fibers, tendrils, catkins, Spanish moss (in south). Slight lining of grass stems, fine rootlets, plant down, spider webs. Invariably long streamers of dried grass, grapevine, fibrous material hang below nest 1-2 ft (0.3-0.6 m), giving it misleading trashy appearance from below. Outside diameter 3.5 in (8.9 cm); inside diameter 1.5 in (3.8 cm), depth 7/8 in (2.2 cm).

EGGS: average size 18.4 x 13.8 mm. Oval to long-oval. Shell smooth, very little or no gloss. Creamy to buffy white, sparingly marked with small brown spots or dots, mainly near large end. Life history accounts are provided by Bent (1942), Mumford (1964), and Walkinshaw (1966).

Diagnostic Characteristics: Adults share similar light eye ring and two whitish wing bars with four other eastern Empidonax flycatchers: Yellow-bellied Flycatcher, Least Flycatcher, Willow Flycatcher, and Alder Flycatcher. When breeding, they are readily distinguishable by voice, habitat, and way of nesting; the nest is unique and unmistakable from other species (refer to Harrison 1975). In late summer and fall, most easily confused with the Yellow-bellied Flycatcher. Both are very green-backed and can have conspicuous yellow wash on the underparts (including the throat). Acadians with yellow throats may also be seen in early spring (before the arrival of the Yellow-bellied, which is typically a late migrant). Despite these similarities, the two species differ in structure: the Acadian is a larger bird, with a larger bill. The Acadian's primary extension is usually conspicuously longer, and the Acadian also has a longer and broader tail. When the Acadian does have yellow on the throat it is usually a clear pale yellow, slightly different from the grayish yellow tones of the Yellow-bellied. Also similar in structure to Alder and Willow Flycatchers, the Acadian usually has a longer primary extension. Its face is paler than that of Willow or Alder, usually contrasting much less with the white throat, and on the Acadian the lower part of the face is usually washed with a fairly bright pale green. The Acadian's call, a loud flat "peek", is very different from the "whit" of Willow Flycatcher, and recognizably different from the "kep" of Alder Flycatcher (Kaufman 1990).
Reproduction Comments: Pair-bonds tend to be long-term (multi-year). Nests late May to mid-August (peak early June to early July) in the mid-Atlantic region (Bushman and Therres 1988). Nests built by female alone. Occasionally nests from previous years are re-used (Whitehead and Greenberg, pers. comms.). Clutch size is 2-4 (usually 3). Incubation, by female, lasts 13-15 days. Young are tended by both parents, leave nest at 13-15 days, fed by parents for about 12 days more. In Ohio, recently fledged young occur from late June through early September, are most abundant in July (Peterjohn and Zimmerman 1989). Individual females produce one or two broods each year. In Maryland, six breeding pairs were found in a 4-ha sample plot (see Bushman and Therres 1988).

NESTING SUCCESS: Walkinshaw (1966) found 319 nests in mixed coniferous-deciduous forests in Michigan: nest success (as a fraction of the number of eggs) was estimated as 57%, 28% of eggs were lost to predation, 4% of eggs were lost to Brown-headed Cowbird (MOLOTHRUS ATER) parasitism, 68% of eggs survived incubation, and 85% survived the nestling stage. Robinson (1992) found only two nests in Illinois: using the Mayfield (1975) Index, daily probability of survival was estimated to be 0.972, with an overall probability of survival of 0.46 (this was the highest survival rate of all open cup-nesting forest birds documented); one nest was parasitized by cowbirds with two cowbird eggs being laid.

Ongoing research by Whitehead (1992) found lower rates of brood parasitism and nest predation in south-central Indiana than found by Robinson (1992) in central Illinois. Whitehead (1992) found only 8.2% of nests to be parasitized by cowbirds overall. Landscape context may explain these lower rates of parasitism and predation: Whitehead (1992) studied interior forest sites (>6 km from fields where cowbirds feed), exterior forest edge sites (forests adjacent to agricultural fields), and forest sites adjacent to young clear cuts, and found both parasitism and predation to be lower in the interior sites. For 257 nests, parasitism was higher in forest adjacent to clearcuts (18.3%) than in either the exterior (4.2%) or the interior (zero) sites. Daily survival rate of nests was highest in the interior sites, intermediate in the exterior sites, and lowest in the clearcut sites. This pattern of daily survival of nests appeared to result almost entirely from differences in predation rate during the nestling stage, and not during either the egg-laying or incubation stages; flycatchers therefore suffered heavy predation during the nestling stage in both of the edge contexts (Whitehead et al., unpubl. data). Whitehead's (1992) preliminary data (1991 and 1992) indicate significant annual variation in demography. In 1991, 11% of nests in interior sites were parasitized, whereas none were parasitized in 1992. In 1991, 33% of nests fledged, whereas 50% fledged in 1992. In 1991, an estimated 54 pairs fledged 55 young, whereas 60 pairs fledged 91 young in 1992.

Ecology Comments: POPULATION DENSITY: Published information on densities from breeding bird censuses in the southeastern U.S. between 1947 and 1979 are summarized by Hamel et al. (1982): mean density was 14.5 pairs/40 ha with a range of 1-43 pairs/40 ha. Two studies of bottomland hardwood forests provide data from similar censusing techniques: Mitchell and Lancia (1990) found densities to be highest within the interior of forests (an average 0.57 birds per 25 m radius 10 minute point count) in South Carolina; on the Roanoke River National Wildlife Refuge in North Carolina, R. Sallabanks (unpubl. data), found highest densities in the interior of small swamp patches (an average 1.48 birds per unlimited radius 10-minute point count) and flycatchers were the second most abundant species detected along the Roanoke River floodplain, after Prothonotary Warblers (PROTONOTARIA CITREA). High numbers were also detected in levee forest patches, an average of 1.37 and 1.32 birds per 10 minute point count being detected in wide and narrow levee patches, respectively. Whitcomb et al. (1981) summarized census data from several studies in Maryland, and found that density decreased from 82 males/square kilometer in mature forest in 1947, to only 48 males/square kilometer in 1976. Stewart and Robbins (1958; cited in Bushman and Therres 1988) reported a density of six breeding pairs on a 13 acre (4 ha) sample plot in an extensive lowland seepage swamp in Maryland. 4.9 territories/40 ha were recorded by Robinson (1992) in Illinois, but numbers have declined to zero in recent years.

TERRITORY SIZE: Quantitative accounts of territory size are rare, although several studies document numbers of males per area (see above). Nesting territory size generally is 0.5-1.7 ha (see Page and Cadman, 1994 COSEWIC report). Bent (1942) cites anecdotal observations which suggest that flycatchers may confine themselves to a narrow territory during the nesting season. Mean territory size in Indiana was found to be 1.63 ha for 15 pairs (Whitehead and Greenberg, pers. comms.). Males apparently maintain their summer territories during their lifetime; Walkinshaw (1966) found eight of 12 males to return to their same identical territories the year after banding. Five returned the next year, two the next, and one the next. Of 19 banded females, six came back the next year to the same territory, all mating with their original mates; five returned the next year, and four the next. Territory size for 80 pairs averaged across all of Walkinshaw's (1966) study areas in Michigan was 2.97 acres. D. R. Whitehead and G. M. Greenberg (pers. comms.) found 100% site fidelity of successful banded males and females in Indiana in 1991 and 1992. Apparently territorial in winter (Stiles and Skutch 1989).

Non-Migrant: N
Locally Migrant: N
Long Distance Migrant: Y
Mobility and Migration Comments: Arrives in nesting area in U.S usually in April-May. Arrives in northern part of nesting range in mid- to late May. Migrates through Costa Rica mid-September to late November and early March to mid-May (Stiles and Skutch 1989). Arrives in Colombia late August, departs by end of April (Hilty and Brown 1986).
Palustrine Habitat(s): FORESTED WETLAND, Riparian
Terrestrial Habitat(s): Forest - Hardwood, Woodland - Hardwood
Habitat Comments: BREEDING: Key habitat requirements are moist deciduous forests with a moderate understory, generally near a stream (Hamel et al. 1982). Humid deciduous forest (primarily mature), woodland, shaded ravines, floodplain forest, river swamps, hammocks and cypress bays of south, thickets, second growth, plantations. Requires a high dense canopy and an open understory (Bushman and Therres 1988). Tends to be scarce or absent in small forest tracts, unless the tract is near a larger forested area (see Bushman and Therres 1988). Floodplain forests must be more than 400-500 feet wide before they become suitable for nesting (Peterjohn and Rice 1991).

Nests in tree in horizontal twig fork toward end of lower branch, often over water, ravine, or other clearing, usually at a height of about 2-9 m. Usually nests on a lower branch, far out from trunk; usually shaded by leafy branches. Average nest characteristics have been measured by D. R. Whitehead and G. M. Greenberg (pers. comms.) for forest interior sites in Indiana: dbh of nest tree - 12.46 cm; nest height - 5.67 m; nest tree height - 14.96 m; distance from bole - 4.37 m; distance to watercourse - 20.74 m; and slope - 18.80 degrees. Bent (1942) describes it as a bird of the forest: it is found in cypress swamps, in heavily wooded bottomlands, and in the depths of wooded ravines. Of Wisconsin, Bent (1942) writes "The essential requirement of the Acadian Flycatcher appears to be a large tract of undisturbed timber. The typical habitat is a deep, well-wooded ravine having a rocky stream bed, which is usually dry. It may also be looked for in the heavy timber of the river bottoms and in tamarack swamps in the southern portion of the state." Conner and Adkisson (1975) found it in mature forest with a basal area of 90 ft squared/acre (21 m squared/ha) (Bushman and Therres 1988).

Vegetation types for the southeastern U.S. from Hanel et al. (1982), in order of suitability, are: oak-gum-cypress and elm-ash-cottonwood are listed as optimal habitat at both the sapling-poletimber, and sawtimber stages; cove hardwoods are listed as suitable at the sapling-poletimber stage and optimal at the sawtimber stage; southern mixed mesic hardwoods are listed as only marginal at the sapling-poletimber stage and optimal at the sawtimber stage; bay swamp-pocosin, oak-hickory, and white pine-hemlock are all listed as only marginal at the sapling-poletimber stage and suitable at the sawtimber stage; mixed pine-hardwood is listed as only marginal at both the sapling-poletimber and sawtimber stages. In all cases, midstory and overstory canopy are used for all activities (feeding/foraging, nesting, perching, roosting, and singing) and dead trees or limbs are used for feeding/foraging and singing. Requires snags for foraging with a minimum dbh of 6 in (15 cm) and exposed perches in the midstory (Hamel et al. 1982). D. R. Whitehead and G. M. Greenberg (pers. comms.) have observed foraging on all types of trees, but usually not snags because they sometimes pick insects off leaves. Data on habitat selection are also given by Hespenheide (1971); where Acadian Flycatchers overlap with Least Flycatchers (EMPIDONAX MINIMUS), the preferred habitat of Acadians has apparently changed in accordance with predictions of competitive effect based on overlap data alone.

MIGRATION: Open scrub and young second growth to primary and secondary forest.

NON-BREEDING: Little is known about this species' wintering habitat. Prefers thickets and gaps in forest understory and edge (Stiles and Skutch 1989). Common resident in understory of humid forest and second growth or cut-over woodland in Colombia (Hilty and Brown 1986). Recorded exclusively in forest in Atlantic lowlands of Costa Rica (Hagan and Johnston 1992). Blake and Loiselle (1992) found them to be most common in old (30-35 year) second-growth forest habitats in Costa Rica. Here, small to medium sized trees (< 25 cm dbh) were most common, as were small vines and lianas; canopy was measured as being 13% open. Also common in young (approximately 5 yr post-abandonment pasture in 1985) second- growth forest habitats; here, the canopy was 26% open and shrubs were the dominant vegetation type. Few were found in primary forest (Blake and Loiselle 1992).

Adult Food Habits: Invertivore
Immature Food Habits: Invertivore
Food Comments: Eats mainly insects obtained by flycatching from perches beneath tree canopy; also gleans insects and eats fruits.
Adult Phenology: Diurnal
Immature Phenology: Diurnal
Length: 15 centimeters
Weight: 14 grams
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: Common throughout much of the eastern U.S. and most often found in deciduous forests near streams, in bottomland hardwoods, and cypress swamps. Key habitat requirements are tall closed canopies and relatively open understories. Being most common in Maryland, North Carolina, and West Virginia, there currently is little conservation concern although Breeding Bird Survey data show signs of gradual decline. The major threat is loss of suitable habitat as natural forests become fragmented, favorable conditions become less common, and cowbird parasitism increases. Few states rank the Acadian Flycatcher with high conservation priority. Studies in Indiana indicate a preference for nesting in areas with high tree density and fairly dense mid- and understory. Stewardship needs are to determine the minimum area requirements for stable breeding populations and long-term monitoring of breeding productivity.
Restoration Potential: Not considered to be degraded in any state; restoration/recovery potential is therefore not applicable at this time. Where the species is of concern (e.g., New Hampshire and Rhode Island), it is on the periphery of its range and has never been a common breeder. Should the species become degraded, restoration seems highly plausible if the correct habitat can be managed for.
Preserve Selection & Design Considerations: Essential features of a preserve designed around this species are that it should primarily consist of moist deciduous forests with a moderate understory, and generally be close to a stream; bottomland hardwood forests are preferred. Reserves should be relatively large (95-300 acres (38-120 ha)), canopies should be high and dense, and the understories open. Snags are required for foraging and should have a minimum dbh of 6 in (15 cm); there should be exposed perches in the midstory. Forest edges, roads, and/or power line corridors that bisect contiguous forest tracts should be avoided since nesting may not occur near edges (e.g., Kroodsma 1982) and flycatchers are generally regarded as forest interior species susceptible to fragmentation (e.g., Whitcomb et al. 1981).

A large contiguous forest much larger than the territory size is required for breeding (Ambuel and Temple 1983). Robbins (1979, 1980) estimated the minimum forest area needed to sustain a viable breeding population at 80 to 125 acres (30-50 ha), and Anderson and Robbins (1981) found the largest percentage in woods of 95 to 300 acres (38-120 ha). Blake and Karr (1984) reported breeding birds in woods as small as 60 acres (24 ha) in Illinois. Whitcomb et al. (1981) found territorial males in forest islands of only 2.5 to 12 acres (1-5 ha) in Maryland, although these were probably in close approximation to larger tracts (Bushman and Therres 1988). Restricted to the interior of forest islands less than 37 acres (15 ha), and populations were only at 44% of maximum in woods less than 173 acres (70 ha) (Whitcomb et al. 1981). According to Bushman and Therres (1988), Kroodsma (1982) found the highest nesting density beyond 200 ft (61 m) from the edge of a power-line corridor, and Chasko and Gates (1982) reported an average nest distance of 149 ft (45 m) from corridors.

Management Requirements: Forest management practices that produce large mature forests with tall closed canopies and high tree density will be favorable for Acadian Flycatchers (Bushman and Therres 1988). Apparently, will tolerate light selection cutting, although any cutting that opens up the canopy would be detrimental (Crawford et al. 1981). R. James (in Page and Cadman, 1994 COSEWIC report) reported that selective logging could be detrimental. Management practices that result in an increase in the understory should also be avoided since this will also cause population decline (Whitcomb et al. 1977). However, in Indiana, Acadian Flycatchers were found to concentrate in sites with dense understories (Whitehead and Greenberg, pers. comms.). Although flycatchers were not found in 1-12 yr old clearcuts by Conner and Adkisson (1977), large clearcuts with long rotations may eventually produce acceptable habitat conditions (Hooper 1978, Bushman and Therres 1988).
Monitoring Requirements: Annual surveys of suitable habitat and known populations using point count censusing techniques are probably the best way to monitor this species. Studies that monitor breeding productivity (e.g., Whitehead 1992, Whitehead et al., unpubl. data) will provide critical information on factors affecting population recruitment and dynamics; it is imperative that we determine why breeding productivity may be low, as well as why numbers of birds may be low.
Management Research Needs: Minimum area requirements seem to be the least well understood aspect of this species' management. Better estimates of minimum viable population size and impacts of habitat fragmentation should also be addressed.
Additional topics: Some research has also been done on the function of singing by females (Kellner and Ritchinson 1988) and song differences and map distances (Payne and Budde 1979).
Population/Occurrence Delineation
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Group Name: Passerines

Use Class: Breeding
Subtype(s): Foraging Area, Nest Site, Nesting Colony
Minimum Criteria for an Occurrence: Evidence of historical breeding, or current and likely recurring breeding, at a given location, minimally a reliable observation of one or more breeding pairs in appropriate habitat. Be cautious about creating EOs for observations that may represent single breeding events outside the normal breeding distribution.

Mapping Guidance: Breeding occurrences include nesting areas as well as foraging areas.

For swallows and other species that have separate nesting and foraging areas, separations are based on nest sites or nesting areas, not to locations of foraging individuals. For example, nesting areas separated by a gap larger than the separation distance are different occurrences, regardless of the foraging locations of individuals from those nesting areas. This separation procedure is appropriate because nesting areas are the critical aspect of swallow breeding occurrences, tend to be relatively stable or at least somwhat predictable in general location, and so are the basis for effective conservation; foraging areas are much more flexible and not necessarily static.

Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: Significant dispersal and associated high potential for gene flow among populations of birds separated by tens of kilometers (e.g., Moore and Dolbeer 1989), and increasing evidence that individuals leave their usual home range to engage in extrapair copulations, as well as long foraging excursions of some species, make it difficult to circumscribe occurrences on the basis of meaningful population units without occurrences becoming too large. Hence, a moderate, standardized separation distance has been adopted for songbirds and flycatchers; it should yield occurrences that are not too spatially expansive while also accounting for the likelihood of gene flow among populations within a few kilometers of each other.

Be careful not to separate a population's nesting areas and foraging areas as different occurrences; include them in the same occurrence even if they are more than 5 km apart. Mean foraging radius (from nesting area) of Brown-headed Cowbird females was 4.0 kilometers in California, 1.2 kilometers in Illinois-Missouri (Thompson 1994). Yellow-headed Blackbirds, Brewer's Blackbirds, and probably Red-winged Blackbirds all forage up to 1.6 kilometers away from breeding colony (Willson 1966, Horn 1968). In one study, Brewer's Blackbirds were found as far as 10 kilometers from nesting area (Williams 1952), but this may be unusual.

For swallows and other parrerines with similar behavioral ecology, separation distance pertains to nest sites or nesting colonies, not to locations of foraging individuals. For example, nesting areas separated by a gap of more than 5 km are different occurrences, regardless of the foraging locations of individuals from those nesting areas. This separation procedure is appropriate because nesting areas are the critical aspect of swallow breeding occurrences, tend to be relatively stable or at least somwhat predictable in general location, and so are the basis for effective conservation; foraging areas are much more flexible and not necessarily static.

Be cautious about creating EOs for observations that may represent single breeding events outside the normal breeding distribution.

Unsuitable habitat: Habitat not normally used for breeding/feeding by a particular species. For example, unsuitable habitat for grassland and shrubland birds includes forest/woodland, urban/suburban, and aquatic habitats. Most habitats would be suitable for birds with versatile foraging habits (e.g., most corvids).

Date: 10Sep2004
Author: Hammerson, G.

Use Class: Migratory stopover
Subtype(s): Foraging Area, Roost Site
Minimum Criteria for an Occurrence: For most passerines: Evidence of recurring presence of migrating individuals (including historical) and potential recurring presence at a given location; minimally a reliable observation of 25 birds in appropriate habitat.

For swallows: Evidence of recurring presence of migrating flocks (including historical) and potential recurring presence at a given location; minimally a reliable observation of 100 birds in appropriate habitat (e.g., traditional roost sites).

Occurrences should be locations where the species is resident for some time during the appropriate season; it is preferable to have observations documenting presence over at least 7 days annually.

EOs should not be described for species that are nomadic during nonbreeding season: e.g., Lark Bunting.

Be cautious about creating EOs for observations that may represent single events.

Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: Separation distance somewhat arbitrary but intended to define occurrences of managable size for conservation purposes. Occurrences defined primarily on the basis of areas supporting concentrations of birds, rather than on the basis of distinct populations.

For swallows and other species with similar behavioral ecology, the separation distance pertains to communal roost sites rather than to foraging areas; the former tend to be more stable and specific over time than the latter.

Date: 03Sep2004
Author: Hammerson, G., and S. Cannings

Use Class: Nonbreeding
Subtype(s): Foraging Area, Roost Site
Minimum Criteria for an Occurrence: Any area used traditionally in the nonbreeding season (used for populations that are not resident in a location year-round). Minimally, reliable observations of 10 or more individuals in appropriate habitat for 20 or more days at a time. For G1-G3 species, observations of fewer individuals could constitute an occurrence of conservation value. Sites used during migration should be documented under the 'migratory stopover' location use class.

Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: Separation distance is necessarily arbitrary but attempts to balance the high mobility of birds with the need for occurrences of reasonable spatial scope. Note that a population's roost sites and foraging areas are parts of the same occurrence, even if they are more than 5 km apart.

For swallows and other species with similar behavioral ecology, the separation distance pertains to communal roost sites rather than to foraging areas; the former tend to be more stable and specific over time than the latter.

Date: 03Sep2004
Author: Hammerson, G.

Use Class: Nonmigratory
Minimum Criteria for an Occurrence: Occurrences are based on evidence of historical presence, or current and likely recurring presence, at a particular location. Such evidence minimally includes collection or reliable observation and documentation of one or more individuals in or near appropriate habitat.

These occurrence specifications are used for nonmigratory populations of passerine birds.

Separation Barriers: None.
Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: Significant dispersal and associated high potential for gene flow among populations of birds separated by tens of kilometers (e.g., Moore and Dolbeer 1989), and increasing evidence that individuals leave their usual home range to engage in extrapair copulations, as well as long foraging excursions of some species, make it difficult to circumscribe occurrences on the basis of meaningful population units without occurrences becoming too large. Hence, a moderate, standardized separation distance has been adopted for songbirds and flycatchers; it should yield occurrences that are not too spatially expansive while also accounting for the likelihood of gene flow among populations within a few kilometers of each other.

Be careful not to separate a population's nesting areas and breeding-season foraging areas as different occurrences; include them in the same occurrence even if they are more than 5 km apart. Blue jays have small summer home ranges but fly up to 4 kilometers to harvest mast (Tarvin and Woolfenden 1999). Flocks of pinyon jays range over 21-29 square kilometers (Ligon 1971, Balda and Bateman 1971); nesting and foraging areas may be widely separated. Tricolored blackbirds forage in flocks that range widely to more than 15 kilometers from the nesting colony (Beedy and Hamilton 1999).

Unsuitable habitat: Habitat not normally used for breeding/feeding by a particular species. For example, unsuitable habitat for grassland and shrubland birds includes forest/woodland, urban/suburban, and aquatic habitats. Most habitats would be suitable for birds with versatile foraging habits (e.g., most corvids).

Date: 10Sep2004
Author: Hammerson, G.
Notes: These specs pertain to nonmigratory species.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Author: Mehlman, D.W.
Management Information Edition Date: 14Sep1993
Management Information Edition Author: SALLABANKS, R.; REVISIONS BY D.W. MEHLMAN
Management Information Acknowledgments: An earlier version of this ESA was improved by the careful reviews of Donald Whitehead, Grant Greenberg and Harry LeGrand, Jr. I also thank Donald Whitehead for kindly providing unpublished reports and data, and Grant Greenberg for providing selected references and notes on Acadian Flycatchers. Thanks also go to all Heritage biologists who responded to the ESA questionnaire: Alabama - Mark Bailey; Arizona - Cindy Osborne; Connecticut - Dawn McKay; Delaware - Christopher Heckcher; Florida - Steve Jones; Georgia - Jon Ambrose; Iowa - Daryl Howell; Illinois - Vernon Kleen; Indiana - John Castrale and Michelle Martin; Kansas - Bill Busby; Kentucky - Brainard Palmer-Ball; Louisiana - Steve Schively; Massachusetts - Brad Blodget; Maryland - Lynn Davidson; Michigan - Mary Rabe; MN - Mary Miller; Missouri - Brad Jacobs; Mississippi - Tom Mann; North Carolina - Harry LeGrand, Jr.; Nebraska - Mary Clausen; New Jersey - Rick Dutko; New York - Kathy Schneider; Ohio - Daniel Rice; Pennsylvania - Barb Barton; Rhode Island - Rick Enser; South Carolina - John Cely; Tennessee - Andrea Shea and Paul Hamel; Virginia - Sarah Mabey; and West Virginia - Barbara Sargent. Judith Soule of the Michigan Natural Features Inventory provided valuable advice on writing the ESA, Bruce Peterjohn of the U.S. Fish and Wildlife Service Office of Migratory Bird Management, Patuxent Research Station sent Breeding Bird Survey data, and Melissa Morrison of The Nature Conservancy's Eastern Regional Office sent ELLINK reports.
Element Ecology & Life History Edition Date: 28Jul1995
Element Ecology & Life History Author(s): Hammerson, G.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

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  • Zammit, A.E., and D.A. Sutherland. 2000. COSSARO Candidate V, T, E Species Evaluation Form for Acadian Flycatcher (Empidonax virescens). Unpublished report prepared by Natural Heritage Information Centre for Committee on the Status of Species at Risk in Ontario (COSSARO), Ontario Ministry of Natural Resources, Peterborough, Ontario. 8 + 4 appendices pp.

  • Zook, J. L. 2002. Distribution maps of the birds of Nicaragua, Costa Rica, and Panama. Unpublished.

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