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"Please observe the scientific name, difficilis, that is, "difficult". There is a delicate irony about the use of this term as a distinctive appellation for one of the "gnat kings*", for, surely, the plural, Empidonaces difficiles, would comprehend them all." -Dawson

*The name Empidonax means "gnat king" in Latin.

Identification
The Pacific-slope Flycatcher is one of several very similar-looking birds called Empidonax flycatchers. It has an olive head and back, lemony and white underparts and a light almond-shaped eyeing thicker behind the eye. Its broad, insect-snarfing bill has a blackish upper mandible and bright orange lower mandible.

Subspecies
According to Pyle (1997) there are three subspecies of Pacific-slope Flycatcher, identified by their breeding ranges. Ours in Andrew Molera State Park is Empidonax difficilis difficilis. It is quite difficult to tell different species of Empidonax flycatchers apart: in fact the Pacific-slope Flycatcher used to be known as the Western Flycatcher until that species was split in two. The other species, the Cordilleran Flycatcher (E. occidentalis) can only be distinguished by listening to the male's song and by the breeding ranges during the summer. Such sibling species as these truly deserve the nickname of "the bane of birdwatchers".

Range
Pacific-slope Flycatchers are neotropical migrants that breed within North America and winter from Mexico to northern South America. Within North America they breed along the Pacific Coast from southernmost Alaska to Baja California, in California's Sierra Nevada, and inland Oregon, western Washington and southern British Columbia.

Song
The song is a series of notes that includes its call note, a sharp seet and an ascending see-yeet note by the male.

Banding History
This species arrives at Andrew Molera State Park in late March and stays over the summer until mid-October. The Big Sur Ornithology Lab has banded 1837 of 2122 birds captured.

Habits
Pacific-slopes have been well studied in Monterey County. The nest is a cup of moss, dry grass, strips of bark, dead leaves and lichens lined with hair and other fine materials. It may be mostly moss but sometimes a lot of human materials are incorporated. Nests can be situated on horizontal limbs low over water, in crevices in rocks, among roots, under bridges, and in buildings. There are usually 4 eggs, incubated by only the female for 14 to 15 days. Both parents tend the nestlings for 15 to 18 days, and fledglings for 13 to 15 more days.

Status
Pacific-slopes aren't a threatened or endangered species. They have probably declined in areas where their forest understory habitat has been removed by humans. They are subject to brood parasitism by Brown-headed Cowbirds and may be declining. A subspecies of a related species, the Southwestern Willow Flycatcher (E. trailli extimus) is endangered due to habitat loss and brood parasitism.

- Lionel Leston

References

VWS Featured Birds:
Townsend's Warbler
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Flycatcher
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