Gloger's rule is an ecogeographical pattern observed in many vertebrates whereby populations in more humid environments have darker pigmentation than populations in more arid environments. The coat color for several species of temperate bats exhibits this pattern, including the Western Long-eared Bat (Myotis evotis) in coastal versus interior populations. We tested Gloger's rule by comparing the coat of M. evotis in the mountains and prairies of Alberta, areas with similar humidity. We predicted that both sets of bats would have similar pigmentation if humidity is the main factor driving variation in coat coloration. Discriminant function analysis of color attributes readily separated M. evotis in the mountains from those in the prairies. Individuals were darker in the mountains, violating Gloger's rule. Differential selection by nocturnal predators against conspicuous coat may explain the color differences we found, and perhaps in other species of temperate bats.