Pacific-slope flycatchers winter in southern Mexico from the southern end of Baja California, along the coastal lowlands of the Pacific coast, to Oaxaca. They breed along the Pacific coast, from northern Baja California to southeastern Alaska. Their range stretches east to the Rocky Mountains in British Columbia, the Cascades in Oregon, and the Sierra Nevada mountains in California.
Biogeographic Regions: nearctic (Native ); neotropical (Native )
occurs (regularly, as a native taxon) in multiple nations
Regularity: Regularly occurring
Type of Residency: Breeding
Regularity: Regularly occurring
Type of Residency: Breeding
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.
Pacific-slope flycatchers are small perching birds around 14 to 17 cm in length and with a mass of 9 to 12 g. They have a relatively large head in comparison to their body, with a faint white to yellow teardrop-shaped patch around each eye. They have broad bills with a lower mandible that varies from yellow to light pink, distinguishing them from other flycatchers. Dull olive or brown feathers comprise the upperparts and back, with more pale and yellow feathers beneath. These flycatchers have relatively short wings (60 to 70 mm), longer tails, gray legs, and faint yellow wing bars.
Western flycatcher species (Pacific-slope and Cordilleran flycatcers) are difficult to distinguish from other flycatchers and each other. The olive-green back, almond-shaped pale eye patch, and gray legs differentiate Pacific-slope flycatchers from yellow-bellied flycatchers (Empidonax flaviventris), Acadian flycatchers (Empidonax virescens) and pine flycatchers (Empidonax affinis). The species are further differentiated by song. Pacific-slope flycatchers are indistinguishable from Cordilleran flycatchers (Empidonax occidentalis) in the field and almost impossible in the hand. However, Pacific-slope flycatchers are more often found in lower elevation, humid forests while Cordilleran flycatchers are often found in higher elevations, in dry coniferous forests.
Range mass: 9 to 12 g.
Range length: 140 to 170 mm.
Range wingspan: 60 to 70 mm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: sexes alike
Length: 14 cm
Weight: 11 grams
Pacific-slope flycatchers breed in humid coniferous, dense second-growth, and mixed deciduous-conifer woodlands. They have been found throughout British Columbia, Washington and Oregon in old-growth Douglas fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla), sugar pine (Pinus lam-bertiana), and incense cedar (Calocedrus decurrens) forests. They are associated with shady, riparian habitats. They are primarily found at elevations from 0 to 1500 m. In British Columbia they have been found in red cedar (Thuja plicata) forests, primarily along dense creek vegetation and ravines, often near lakes and ponds. In Mexico, they winter in mountainous conifer forests, tropical deciduous forests, and tropical lowland evergreen forests.
Range elevation: 0 to 1500 m.
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: taiga ; forest
Other Habitat Features: riparian
Habitat and Ecology
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).
Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.
Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.
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).
Pacific-slope flycatchers feed almost entirely on insects caught in the air or on tree and bush leaves. They prefer to forage in the middle and lower canopy of forests. They use a hawking method of prey capture; sallying forth from a perch to catch insects on the wing, then returning to the perch. Their main foods are bees, wasps, moths, spiders, flies, and other insects, though they occasionally consume vegetation like blackberry and elderberry leaves.
Animal Foods: insects
Plant Foods: leaves
Primary Diet: carnivore (Insectivore )
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.
Pacific-slope flycatchers are predators to many insects and spiders and in turn are consumed by hawks, squirrels, snakes, jays, and other predatory birds. They are parasitized by brown-headed cowbirds (Molothrus ater). Aside from this, little else is known about the role of these flycatchers in their ecosystem.
Little is known about predation on Pacific-slope flycatchers. However it is likely that they are vulnerable to the main predators of other small, forest birds, including hawks, squirrels, snakes, and jays. Records exist of both Steller's jays (Cyanocitta stelleri) and scrub jays (Aphelocoma californica) preying on Pacific-slope flycatcher nests.
- Steller's jays (Cyanocitta stelleri)
- scrub jays (Aphelocoma californica)
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: > 300
Comments: This species is represented by a large number of occurrences (subpopulations).
Comments: Total adult population size is unknown but likely exceeds 1,000,000. Rich et al. (2004) estimated population size at 8,300,000.
Life History and Behavior
Only males sing and the song primarily seems to serve to attract mates and delineate territories. Males sing extensively during the breeding season, but both males and females can give alarm calls in the presence of danger or predators.
Communication Channels: visual ; acoustic
Perception Channels: visual ; tactile ; acoustic ; chemical
Longest lifespan in the wild is recorded at 6 years based on museum specimens. Longevity in captivity and expected lifespan is unknown
Status: wild: 6 (high) years.
Status: wild: 6.0 years.
Lifespan, longevity, and ageing
Pacific-slope flycatchers are mostly monogamous. A single study done on mating Pacific-slope flycatchers in British Columbia reported that 1 in 7 males partnered with 2 females.
Mating System: monogamous ; polygynous
Pacific-slope flycatchers usually hatch several broods in a given breeding season from mid April to mid July. In Monterey County, California they have been found to build nests from April 15 to May 1 for first broods and June 1 to July 15 for second broods and re-nesting. Mean clutch size is four eggs per brood. Incubation time lasts between 13 and 16 days and fledging time is around 14 to 17 days after hatching. Age is presumed to be one year at first breeding and they breed annually afterwards.
Breeding interval: Pacific-slope flycatchers breed once annually.
Breeding season: Pacific-slope flycatchers breed from mid-April through mid-July.
Average eggs per season: 4.
Range time to hatching: 13 to 16 days.
Range fledging age: 14 to 17 days.
Range time to independence: 14 to 17 days.
Average age at sexual or reproductive maturity (female): 1 years.
Average age at sexual or reproductive maturity (male): 1 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous
The female alone incubates the eggs but both sexes bring food to the fledgling young and remove fecal sacs.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female, Protecting: Male, Female)
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).
Molecular Biology and Genetics
Barcode data: Empidonax difficilis
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Empidonax difficilis
Public Records: 5
Specimens with Barcodes: 11
Species With Barcodes: 1
While long term population trends have not been quantified, Pacific-slope flycatchers are a species of Least Concern by the IUCN Redlist. They are not listed under the U.S. Endangered Species act or the Convention on International Trade in Endangered Species. They are listed and protected under the U.S. Migratory Bird Treaty Act. Breeding Bird Survey data show no significant declines of this species between 1966 and 1996.
US Migratory Bird Act: protected
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
IUCN Red List Assessment
Red List Category
Red List Criteria
National NatureServe Conservation Status
Rounded National Status Rank: N5B - Secure
Rounded National Status Rank: N5B - Secure
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Reasons: Large range in western North America; numerous subpopulations; large population size; relatively stable.
Global Short Term Trend: Relatively stable (=10% change)
Comments: Three generations likely is about 10 years, and there is no evidence of a significant range-wide decline over the past 10 years.
Global Long Term Trend: Increase of 10-25% to decline of 30%
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).
Degree of Threat: Low
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.
Preserve Selection and 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).
Global Protection: Very many (>40) occurrences appropriately protected and managed
Relevance to Humans and Ecosystems
There are no known adverse effects of Pacific-slope flycatchers on humans.
Aside from controlling insect populations, there are few other documented benefits to humans.
Positive Impacts: controls pest population
The Pacific-slope flycatcher (Empidonax difficilis) is a small insectivorous bird of the family Tyrannidae. It is native to coastal regions of western North America, including the Pacific Ocean and the southern Gulf of California, as far north as British Columbia and southern Alaska, but is replaced in the inland regions by the Cordilleran flycatcher. These two species were formerly considered a single species known as the western flycatcher. In winter, both species migrate south to Mexico, where they are virtually indistinguishable from one another.
In plumage, the Pacific-slope flycatcher is virtually identical to the Cordilleran flycatcher, and differs only subtly from most Empidonax flycatchers in North America, but its breeding habitat and call are different. Its call can vary slightly by different regions and the bird itself.
The Pacific-slope flycatcher inhabits either coniferous or deciduous forests. In its range it enters mixed woods, Douglas fir forests, redwood forests, and many other wooded environments including riparian woodlands.
As a flycatcher it will wait on a perch and when it sees a flying insect it will chase it without any apparent effort. They also enter swarms of gnats, mosquitos and wherever such insects congregate. They fulfill an important role in keeping insect populations in check, particularly mosquitoes. and they also eat caterpillars and spiders.
Names and Taxonomy
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).