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 Sea of Cortez, 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 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 insects, particularly mosquito's population in check.