For those not familiar with conventions of scientific citation, here's how it works. Any time a statement is made that is not based on the original research of the author, the person responsible who did make that particular discovery or offer that particular opinion must be credited, by means of a scientific citation. In some forms of scholarship, this is done with footnotes. Scientific publications, however, use a different convention, which is followed throughout this work. After the statement in the text, the name(s) of the author(s) and year of publication of the information are enclosed in parentheses. If the name(s) of the author(s) is mentioned in the text, then only the year of publication is enclosed in parentheses. The full reference is given in the "Literature Cited" section, which includes only references cited in the text, and is therefore not the same as a bibliography. Cited references are arranged alphabetically by author (s) and year of publication. When a publication has more than two authors, it is typically cited in the text as First Author "et al." All authors' names are given in the Literated Cited section. I follow the conventions of The Auk, flagship publication of the American Ornithologists' Union, except that I spell out the names of the scientific serials (journals and monograph series) in which articles are published, instead of using standard abbreviations.

American Ornithologists' Union. 1989. Thirty-seventh supplement to the American Ornithologists' Union Check-list of North American birds. Auk 106:532-538.

American Ornithologists' Union. 1998. Check-list of North American birds. 7th ed. American Ornithologists' Union, Washington, D. C.

Bailey, S. F. 1983. Western Flycatcher Empidonax difficilis. Pp. 268-269 in The Audubon Society master guide to birding. Vol. 2. Gulls to dippers.(J. Farrand, Jr. Ed.) Alfred A. Knopf, New York.

Davis, J., G.F. Fisler, and B.S. Davis. 1963. The breeding biology of the Western Flycatcher. Condor 65:337-382.

Johnson, N.K. 1980. Character variation and evolution of sibling species in the Empidonax difficilis-flavescens complex (Aves: Tyrannidae). University of California Publications in Zoology. 112:1-151.

Johnson, N.K. 1994. Old-school taxonomy versus modern biosystematics: Species-level decisions in Stelgidopteryx and Empidonax. Auk 111: 773-780.

Johnson, N.K. and J.A. Marten. 1988. Evolutionary genetics of flycatchers. II. Differentiation in the Empidonax dificilis complex. Auk 105: 177-191.

Kaufman, K. 1990. A field guide to advanced birding. Houghton Mifflin Co., Boston, MA.

Whitney, B. and K. Kaufman. 1985. The Empidonax challenge, part 2. Least, Hammond's, and Dusky flycatchers. Birding 17: 277-287.

Whitney, B. and K. Kaufman. 1986a. The Empidonax challenge: looking at Empidonax. Part III: the Alder/Willow problem (Empidonax traillii and E. alnorum). Birding 28:153-159.

Whitney, B. and K. Kaufman. 1986b. The Empidonax challenge: looking at Empidonax. Part IV. Acadian, Yellow-bellied, and Western flycatchers (Empidonax virescens, E. flaviventris, and E. dificilis, respectively). Birding 18: 315-327.

Whitney, B. and K. Kaufman. 1987. The Empidonax challenge. Part 5. Birding 19:7-15.