The study of geographic variation has probably taken up a well-known place in ornithology. For decades, most of researchers interested in evolutionary trends in birds focused on the study of geographic variation (e.g. Morrison 1983, Zink 1986, Atwood 1988, Johnson and Marten 1992, Johnston 1994, Roselaar 1995, Engelmoer and Roselaar 1998, Johnson 2002).

Study of the geographic variation in birds usually focused on morphologic variation, and the insights from the morphologic variation were used to solve the taxonomic problems (Johnson and Marten 1992, Escalente-Piliego and Peterson 1992, Johnson 2002). In addition to taxonomic problems, some other researchers of geographic variation in birds have also interested in the geography of intrapopulation variability to test ecological importance of morphological variation (James 1970, Aldrich 1984, Grant and Grant 1986, 1989, 2008, Kaboli 2007).

Thus, it is plausible to say that geographic variation is one of the most famous study topics in evolutionary biology. In this mini review, I concentrate on two main topics – taxonomy, and adaptation and speciation – and their relationships with geographic variation.