References

Brown, C.R. and M. Bomberger Brown. 1995. Cliff Swallow (Hirundo [Petrochelidon] pyrrhonota). In: The Birds of North America, No 149 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia and The American Ornithologists’ Union, Washington, D.C.

Brown, C.R. and M. Bomberger Brown. 1996. Coloniality in the Cliff Swallow: the Effect of Group Size on Social Behavior. University of Chicago Press, Chicago, IL

Cliff Swallow (Petrochelidon pyrrhonota). Cornell Lab of Ornithology, http://www.allaboutbirds.org/guide/Cliff_Swallow/id