Empidonax traillii, commonly known as the Willow Flycatcher, is a small bird found in North America, particularly in shrubby wetlands and riparian areas. It is known for its distinctive 'fitz-bew' song and its olive-brown plumage with a pale throat and belly. This insectivorous bird plays a crucial role in controlling insect populations.

Empidonax traillii, commonly known as the Willow Flycatcher, is native to North America. Its geographical distribution includes parts of Canada, the United States, and Mexico. In Canada, it is mainly found in southern regions such as British Columbia and Alberta. In the United States, it ranges broadly across the western and central parts, including states like California, Arizona, and New Mexico. The species is also present in northern Mexico.

The Willow Flycatcher thrives in riparian habitats, which are environments adjacent to rivers and streams. These areas are characterized by dense thickets of willow trees, shrubs, and other moist or wetland vegetation. The climate in these habitats can vary from temperate in northern regions to more arid in the southern parts of its range, but the presence of water is a consistent requirement.

As an insectivorous bird, the Willow Flycatcher plays a role in controlling insect populations. It is often found in areas with abundant insect life, which it catches on the wing. The bird is also known for its distinctive 'fitz-bew' call, which it uses to establish territory and attract mates during the breeding season. Willow Flycatchers are migratory and adapt their behaviors and habitats according to seasonal changes, wintering in Central America.