Sedgwick, James A. 2000. “Willow Flycatcher (Empidonax traillii).” The Birds of North America, edited by Paul G. Rodewald. Ithaca: Cornell Lab of Ornithology. Retrieved from the Birds of North America: https://birdsna.org/Species-Account/bna/species/wilfly doi: 10.2173/bna.533