Pacific-slope Flycatcher

Pacific-slope Flycatcher

By Andrew McCormick

PC: Mick Thompson (Pacific-slope Flycatcher)

PC: Mick Thompson (Pacific-slope Flycatcher)

Scientific Name: Empidonax difficilis

Length 5.5 in

Wingspan 8 in

Weight 0.39 oz

AOU Band code PSFL

The Pacific-slope Flycatcher was formerly considered the same species as the Cordilleran Flycatcher Empidonax occidentalis and known as the Western Flycatcher. It is slightly smaller than the Cordilleran and is generally found west of the divide along the Cascade and Sierra Nevada mountain ranges. It is one of 11 North American flycatchers in the genus Empidonax, from the Greek for gnat master combining empid, a mosquito or gnat, and anax, lord or master, in reference to its feeding habit of hawking insects. The differences among the empids are slight and this bird is very difficult to identify by sight alone.  Hence the species name difficilis.   

Identification of male empids is accomplished primarily from their vocalizations and most reliably on the breeding grounds. Females do not sing. The Pacific-slope Flycatcher’s signature position note is an upward slurred tsweep.  This is very similar to the Cordilleran’s.  This note distinquishes both species from other empids. The location west of the Cascades will separate the Pacific-slope from the Cordilleran most of the time. Further study is needed in the area where both species are present to determine if this separation of species will remain permanent.

The Pacific-slope Flycatcher is a medium-size empid with a somewhat large head and a teardrop eye ring pointed behind the eye and broken at the top. Its wings are relatively shorter than other empids and the primary feathers have a short projection when folded giving the tail a longer look. Its upperparts are olive green but turn grayer as the feathers age in summer. Its legs are gray and its bill is bicolored with the lower mandible being yellow-orange to pinkish (Louther).  Although difficult to see in the moist woodlands the bird favors, the bill color can be a very good field mark.

The breeding range of the Pacific-slope Flycatcher is along the Pacific coast of California, the northwestern United States and British Columbia. The species is a medium-distance migrant which arrives on the breeding grounds in May and early June. Opportunistic in finding nesting sites these flycatchers will not only build in the fork of a tree, but also on a ledge in a stream bank, a stump, the upturned roots of a fallen tree, or shed rafters.  Generally all of these sites will be within 10 feet of the ground. Three to four whitish eggs with brown blotches will be deposited in the nest made of moss, grass, rootlets, strips of bark, lichens and leaves. Only the female incubates the eggs but both parents will bring food to the nestlings (Kaufman). Incubation lasts about two weeks and first flight occurs in another two weeks. There are many instances of a second brood in a season.

The population of Pacific-slope Flycatchers seems stable.  However, the species is at risk from human intervention. Care should be taken in “cleaning up” woodland areas.  Clearing downed trees and brush in Pt Lobos Reserve in Monterey Co., CA resulted in extirpation of the species as nesting sites were lost (Louther).