For assistance in our own Cliff Swallow research, we thank the 77 research assistants who did field work in western Nebraska from 1982-2016, Amy Moore and Catherine Page for data management, and Erin Roche for collaboration on analyses. For providing facilities during field work, we thank the Cedar Point Biological Station of the University of Nebraska-Lincoln. For financial support we thank the National Science Foundation, the National Institutes of Health, the Erna and Victor Hasselblad Foundation, the National Geographic Society, the American Philosophical Society, Yale and Princeton universities, the Cedar Point Biological Station, the Chapman Fund of the American Museum of Natural History, the National Academy of Sciences, Sigma Xi, Alpha Chi, and the University of Tulsa. For allowing use of unpublished information, we thank Veronica Bowers, Cas Bridge, Peter Burke, Peter Goldman, Cluff Hopla, Alvaro Jaramillo, Allison Johnson, Lloyd Kiff and the Western Foundation of Vertebrate Zoology, Carroll D. Littlefield, Jenella Loye, Eugene Morton, Michael Patten, Peter Pyle, Letitia Reichart, Carlos Rengifo, Mara Silver, Steven Speich, Philip Stoddard, Bill Summerour, and Jakob Unger.