Empidonax difficilis
Pacific-slope flycatcher

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. (American Ornithologists’ Union, 1998; Lowther, 2005)

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. (American Ornithologists’ Union, 1998; Campbell, et al., 1997)

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. (Lowther, 2005)

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. (Ainsley, 1992)

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. (Lowther, 2005)

The female alone incubates the eggs but both sexes bring food to the fledgling young and remove fecal sacs. (Lowther, 2005)

Longest lifespan in the wild is recorded at 6 years based on museum specimens. Longevity in captivity and expected lifespan is unknown (Lowther, 2005)

Like other flycatchers, Pacific-slope flycatchers feed by sitting on an exposed perch and sallying forth to catch insects from the air and from leaves. Pacific-slope flycatchers migrate annually between wintering and breeding ranges. They are mainly solitary outside of the breeding season. (Davis, et al., 1963; Lowther, 2005)

They are territorial and typical territory size is between 1.5 and 3.5 hectares. They typically defend their territory from conspecifics by giving chase, chirping, buzzing, snapping their bills and occasionally locking feet with a rival and fluttering to the ground. (Davis, et al., 1963; Lowther, 2005)

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. (Ainsley, 1992; Davis, et al., 1963; Lowther, 2005)

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. (Lowther, 2005)

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. (Lowther, 2005)

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. (Lowther, 2005)

Aside from controlling insect populations, there are few other documented benefits to humans. (Lowther, 2005)

There are no known adverse effects of Pacific-slope flycatchers on humans.

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. (Lowther, 2005)