Brown, Charles R., Mary B. Brown, Peter Pyle, and Michael A. Patten. 2017. ā€œCliff Swallow (Petrochelidon pyrrhonota).ā€ 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/cliswa