The Cordilleran flycatcher (Empidonax occidentalis), with its seasonal territories extending from the U.S.-Canadian border to southern Mexico, is found primarily in the Rocky Mountains. It belongs to the order Passeriformes and the family Tyrannidae (Lowther et al 2016). The preferred habitat for E. occidentalis is mainly deciduous or mixed deciduous-coniferous forests and shady canyons, but while breeding they are found in mountainous regions and they forage in conifers like Douglas Fir and various pines. They tend to inhabit slightly drier and more open areas than the almost identical Pacific-slope flycatcher (E. difficilis), which is found in the coast mountain ranges of the West, rather than in the Rockies (Kaufman 2018).
The adult Cordilleran flycatcher has yellow-olive to olive coloration on its back with a yellow underside, the yellow extending up to the throat under its broad bill (Lowther et al 2016). It has prominent olive and white wing-bars and pale yellow eye rings which form into a teardrop shape. It also typically has four long, olive-brown tail feathers. Both males and females are approximately 5.5-6.7 inches in length, weigh about 0.4-0.5 ounces, and have a wingspan of roughly 8.7 inches. The juveniles look very similar to the adults, but they have distinct buffy wing-bars that transition to white and olive as they mature (All About Birds 2018). This bird is difficult to spot since it is small in size but can be identified by the male’s call, a thin, high-pitched, distinctly two-part tii-seet, which differs somewhat from the upslurred tseeweep of E. difficilis (Sibley 2003).
The Cordilleran flycatcher has a distinctive feeding behavior, as it watches from a perch and then flies out to catch insects in the air or from trees and shrubs. Its diet consists mostly of insects, including wasps, bees, flies, caterpillars, moths, and beetles. The parents deliver the food to the nestlings until they take their first flight, which occurs between 14-18 days. Since the Cordilleran flycatcher is rarely spotted, it is apparently a relatively solitary bird that spends most of its maintenance time alone (Kaufman 2018).
E. occidentalis usually lays three to four white eggs with brown blotches concentrated near the larger end, which are incubated for about 14-15 days. Nest sites are either in a small tree, in a cleft in a vertical streambank, on a stump, or in the upturned roots of a fallen tree. The nests are built by the female and are made up of moss, grass, roots, leaves, and feathers. When the Cordilleran flycatcher migrates, it usually arrives at breeding grounds in May and leaves in September (All About Birds 2018).
Data from the Breeding Bird Survey for E. occidentalis is combined with that for E. difficilis and shows that the estimated population for both species in the United States and Canada is 8.3 million individuals (Lowther et al 2016).
