This thesis examines the effects that Pleistocene glaciation had on the population structure and contemporary genetic patterns of the hairy woodpecker (Picoides villosus). A combination of molecular markers, revealed reduced levels of gene flow among groups of hairy woodpeckers. Microsatellite analyses suggest barriers to gene flow have influenced contemporary population structure, with higher structure found in western North America where barriers to gene flow are more prevalent. MtDNA analyses revealed three distinct genetic lineages, two in North America and a third in Central America. Results indicate these lineages separated prior to the Wisconsin glaciation (~100 kya) and that contemporary population structure is the result of post-glacial expansion from multiple refugia following deglaciation. Current taxonomy recognizes 17 subspecies (Jackson et al., 2002), but molecular analyses in this study do not support current subspecies designations. / xii, 117 leaves ; 29 cm