Empidonax traillii extimus is one of several recognized subspecies of the Willow Flycatcher (Unitt 1987; Browning 1993), a neotropical migrant that breeds across much of North America. This southwestern race is a riparian obligate, nesting in dense patches of willow (Salix spp.), willow–cottonwood(Populus spp.), or other similarly structured habitats.