The nest is built of shredded bark, cattail tufts, and grasses, and lined with fine grasses and feathers. Usually it is placed in a branch fork in a willow, near water. The eggs are buff with dark spots at one end. Extensive population reductions since the 1800s have been inferred from comparison of historical to current occurrences. It is also considered endangered in California and New Mexico.
Much smaller populations exist in Nevada, Utah, Colorado, and Texas.
The southwestern willow flycatcher is federally listed as endangered.