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