Appearance
Adults have brown-olive upperparts, darker on the wings and tail, with whitish underparts; they have an indistinct white eye ring, white wing bars and a small bill. The breast is washed with olive-gray. The upper part of the bill is gray; the lower part is orangish. At one time, this bird and the alder flycatcher were considered to be a single species, Traill's flycatcher. The willow and alder flycatchers were considered the same species until the 1970s. Their song is the only reliable method to tell them apart in the field .Their breeding habitat is deciduous thickets, especially willows and often near water, across the United States and southern Canada. They make a cup nest in a vertical fork in a shrub or tree.
These neotropical birds migrate to Mexico and Central America, and in small numbers as far south as Ecuador in South America, often selecting winter habitat near water. Willow flycatchers travel approximately 1,500–8,000 km each way between wintering and breeding areas.
They wait on a perch near the top of a shrub and fly out to catch insects in flight, also sometimes picking insects from foliage while hovering. They may eat some berries.
This bird's song is a sneezed ''fitz-bew''. The call is a dry ''whit''.
This bird competes for habitat with the alder flycatcher where their ranges overlap.

Naming
The subspecies are best distinguished from each other by their songs. In addition, the four subspecies have significant genetic differences based on mitochondrial DNA analysis. Their winter ranges have been elucidated using mitochondrial DNA genetic studies of 172 birds sampled in winter combined with plumage coloration and morphological differences.The four subspecies of the willow flycatcher are:
Habitat
Adults have brown-olive upperparts, darker on the wings and tail, with whitish underparts; they have an indistinct white eye ring, white wing bars and a small bill. The breast is washed with olive-gray. The upper part of the bill is gray; the lower part is orangish. At one time, this bird and the alder flycatcher were considered to be a single species, Traill's flycatcher. The willow and alder flycatchers were considered the same species until the 1970s. Their song is the only reliable method to tell them apart in the field .Their breeding habitat is deciduous thickets, especially willows and often near water, across the United States and southern Canada. They make a cup nest in a vertical fork in a shrub or tree.
These neotropical birds migrate to Mexico and Central America, and in small numbers as far south as Ecuador in South America, often selecting winter habitat near water. Willow flycatchers travel approximately 1,500–8,000 km each way between wintering and breeding areas.
They wait on a perch near the top of a shrub and fly out to catch insects in flight, also sometimes picking insects from foliage while hovering. They may eat some berries.
This bird's song is a sneezed ''fitz-bew''. The call is a dry ''whit''.
This bird competes for habitat with the alder flycatcher where their ranges overlap.
References:
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