Empidonax difficilis - Baird, 1858
Pacific-slope Flycatcher
Taxonomic Status: Accepted
Related ITIS Name(s): Empidonax difficilis S. F. Baird, 1858 (TSN 178348)
French Common Names: Moucherolle côtier
Spanish Common Names: Mosquero Californiano
Unique Identifier: ELEMENT_GLOBAL.2.103795
Element Code: ABPAE33120
Informal Taxonomy: Animals, Vertebrates - Birds - Perching Birds
Image 11441

© Larry Master

 
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 difficilis
Taxonomic Comments: This species formerly was regarded as conspecific with E. occidentalis (AOU 1998). Johnson and Marten (1988) examined variation in the E. difficilis group and concluded that E. difficilis and E. occidentalis are distinct species. Phillips (1994) argued that existing information does not justify the recognition of E. occidentalis and E. difficilis as distinct species. Johnson (1994) provided additional analyses indicating that E. difficilis and E. occidentalis warrant separate-species status. Form insulicola (Channel Islands flycatcher) may be a distinct species (AOU 1998). Empidonax difficilis, E. occidentalis, and E. flavescens constitute a superspecies(AOU 1998).
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
Reasons: Large range in western North America; numerous subpopulations; large population size; relatively stable.
Nation: United States
National Status: N5B (19Mar1997)
Nation: Canada
National Status: N5B,NUM (02Jan2018)

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 Alaska (S4B), Arizona (S4M), California (SNR), Nevada (S3M), Oregon (S4B), South Dakota (S4B), Washington (S4S5B)
Canada Alberta (SUB), British Columbia (S5B)

Other Statuses

IUCN Red List Category: LC - Least concern

NatureServe Global Conservation Status Factors

Range Extent: 200,000-2,500,000 square km (about 80,000-1,000,000 square miles)
Range Extent Comments: Nesting range extends from southeastern Alaska and northwestern and central British Columbia (including Queen Charlotte and Vancouver islands) south to southwestern California (generally west of Cascades and Sierra Nevada) and mountains of northern and southern Baja California (AOU 1998, Lowther 2000). Range in southeastern British Columbia, Alberta, and north-central and northeastern Washington is uncertain and in need of further study. Winter range is mainly along Pacific coast lowlands of Mexico (0-1,500 meters elevation) from southern Baja California and northwestermn Mexico (southern Sonora) south to Oaxaca west of the Isthmus of Tehuantepec, rarely north to California and Arizona (Howell and Webb,1995, AOU 1998, Lowther 2000).

The insulicola group is resident in the Channel Islands off southern California (AOU 1989).

Coded range extent refers to nesting range.

Number of Occurrences: > 300
Number of Occurrences Comments: This species is represented by a large number of occurrences (subpopulations).

Population Size: >1,000,000 individuals
Population Size Comments: Total adult population size is unknown but likely exceeds 1,000,000. Rich et al. (2004) estimated population size at 8,300,000.

Number of Occurrences with Good Viability/Integrity: Very many (>125)

Overall Threat Impact: Low
Overall Threat Impact Comments: Certainly habitat alteration is a threat to local populations, but overall this species faces no major threats. This species often nests on buildings and does not require pristine habitat.

Short-term Trend: Relatively Stable (<=10% change)
Short-term Trend Comments: Three generations likely is about 10 years, and there is no evidence of a significant range-wide decline over the past 10 years.

Long-term Trend: Decline of <30% to increase of 25%
Long-term Trend Comments: Breeding Bird Survey (BBS) data for 1966-2007 indicate a range-wide decline of 1.0% per year, but the trend is not statistically significant.

Range of "western flycatcher" may have expanded eastward and northward in British Columbia since the mid-1940s (Campbell et al. 1997).

Other NatureServe Conservation Status Information

Distribution
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Global Range: (200,000-2,500,000 square km (about 80,000-1,000,000 square miles)) Nesting range extends from southeastern Alaska and northwestern and central British Columbia (including Queen Charlotte and Vancouver islands) south to southwestern California (generally west of Cascades and Sierra Nevada) and mountains of northern and southern Baja California (AOU 1998, Lowther 2000). Range in southeastern British Columbia, Alberta, and north-central and northeastern Washington is uncertain and in need of further study. Winter range is mainly along Pacific coast lowlands of Mexico (0-1,500 meters elevation) from southern Baja California and northwestermn Mexico (southern Sonora) south to Oaxaca west of the Isthmus of Tehuantepec, rarely north to California and Arizona (Howell and Webb,1995, AOU 1998, Lowther 2000).

The insulicola group is resident in the Channel Islands off southern California (AOU 1989).

Coded range extent refers to nesting range.

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 AK, AZ, CA, NV, OR, SD, WA
Canada AB, BC

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; WILDSPACETM 2002

Ecology & Life History
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Reproduction Comments: Clutch size is 3-4. Incubation, by female, lasts 14-15 days. Nestlings are tended by both parents, leave nest in 14-18 days, fed for 10-11 more days (Harrison 1978).
Non-Migrant: Y
Locally Migrant: Y
Long Distance Migrant: Y
Mobility and Migration Comments: Breeding populations in U.S. (except Channel Islands population) move out of U.S. for winter. Arrives in U.S. nesting areas March-May (Terres 1980).
Palustrine Habitat(s): Riparian
Terrestrial Habitat(s): Cliff, Forest - Conifer, Forest - Hardwood, Forest - Mixed, Forest/Woodland, Woodland - Conifer, Woodland - Hardwood, Woodland - Mixed
Special Habitat Factors: Standing snag/hollow tree
Habitat Comments: Nesting habitat includes humid coniferous forest (mostly coastal), pine-oak forest and other mixed coniferous-deciduous forests, broadleaf evergreen forest, dense second-growth woodland, and riparian woodlands, often where open areas exist under the canopy of large trees and favoring shady ravines in some areas (AOU 1998, Lowther 2000). In more open and drier habitats on Channel Islands, this flycatcher occurs among eucalyptus shade trees or in oak clumps in canyon bottoms, foraging over coastal scrub and opuntia cactus (Johnson 1980). Nests are placed on cliffs, earth banks, tree branch crotches, or building ledges, or in tree cavities, often along streams or near seeps or springs.

In migration, Pacific-slope flycatchers tend to associate with shady habitats. Wintering occurs in montane evergreen forest, gallery forest, tropical deciduous forest, and tropical lowland evergreen forest (AOU 1998).

Adult Food Habits: Invertivore
Immature Food Habits: Invertivore
Food Comments: Primarily insectivorous; feeds mainly on Hymenoptera, Coleoptera, Diptera, and Lepidoptera. Also feeds on some berries and seeds. Usually forages by flying out from a perch and catching insects in the air.
Adult Phenology: Diurnal
Immature Phenology: Diurnal
Length: 14 centimeters
Weight: 11 grams
Economic Attributes Not yet assessed
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Management Summary
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Preserve Selection & Design Considerations: In a study in a northwestern California Douglas-fir forest, western flycatcher (EMPIDONAX DIFFICILIS) avoided edges, yet did not respond negatively to forest fragmentation. Positive association to the proximity and length of clearcut edges and positively correlated with stands that were more insular, or contained more clearcuts and total edge (Rosenberg and Raphael 1986).
Management Requirements: Prefers old forests over younger stands (Raphael et al. 1988, Carey et al. 1991, Manuwal 1991). In an Oregon Cascades study, the species favored old stands and areas with decayed logs, fern and deciduous shrub cover, western hemlocks (TSUGA HETEROPHYLLA) and very large western redcedar (THUJA PLICATA); the authors suggested that older stands probably best meet the species need for open flying space for feeding (Gilbert and Allwine 1991). In mature, unmanaged forest stands, average abundances are slightly higher along streamsides than in upslope stands, but not significantly so (McGarigal and McComb 1992).
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 Edition Date: 06Mar2009
NatureServe Conservation Status Factors Author: Hammerson, G.
Management Information Edition Author: PAIGE, C.; REVISIONS BY D.W. MEHLMAN
Element Ecology & Life History Edition Date: 06Mar2009
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).

References
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Note: All species and ecological community data presented in NatureServe Explorer at http://explorer.natureserve.org were updated to be current with NatureServe's central databases as of March 2019.
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Citation for data on website including State Distribution, Watershed, and Reptile Range maps:
NatureServe. 2019. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia. Available http://explorer.natureserve.org. (Accessed:

Citation for Bird Range Maps of North America:
Ridgely, R.S., T.F. Allnutt, T. Brooks, D.K. McNicol, D.W. Mehlman, B.E. Young, and J.R. Zook. 2003. Digital Distribution Maps of the Birds of the Western Hemisphere, version 1.0. NatureServe, Arlington, Virginia, USA.

Acknowledgement Statement for Bird Range Maps of North America:
"Data provided by NatureServe in collaboration with Robert Ridgely, James Zook, The Nature Conservancy - Migratory Bird Program, Conservation International - CABS, World Wildlife Fund - US, and Environment Canada - WILDSPACE."

Citation for Mammal Range Maps of North America:
Patterson, B.D., G. Ceballos, W. Sechrest, M.F. Tognelli, T. Brooks, L. Luna, P. Ortega, I. Salazar, and B.E. Young. 2003. Digital Distribution Maps of the Mammals of the Western Hemisphere, version 1.0. NatureServe, Arlington, Virginia, USA.

Acknowledgement Statement for Mammal Range Maps of North America:
"Data provided by NatureServe in collaboration with Bruce Patterson, Wes Sechrest, Marcelo Tognelli, Gerardo Ceballos, The Nature Conservancy-Migratory Bird Program, Conservation International-CABS, World Wildlife Fund-US, and Environment Canada-WILDSPACE."

Citation for Amphibian Range Maps of the Western Hemisphere:
IUCN, Conservation International, and NatureServe. 2004. Global Amphibian Assessment. IUCN, Conservation International, and NatureServe, Washington, DC and Arlington, Virginia, USA.

Acknowledgement Statement for Amphibian Range Maps of the Western Hemisphere:
"Data developed as part of the Global Amphibian Assessment and provided by IUCN-World Conservation Union, Conservation International and NatureServe."

NOTE: Full metadata for the Bird Range Maps of North America is available at:
http://www.natureserve.org/library/birdDistributionmapsmetadatav1.pdf.

Full metadata for the Mammal Range Maps of North America is available at:
http://www.natureserve.org/library/mammalsDistributionmetadatav1.pdf.

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