We compared the external morphology of western long-eared myotis (Myotis evotis) living in mountain (cool, wet) and prairie (warm, dry) environments in southern Alberta to test whether flight permits genetic exchange between populations thereby limiting divergence in morphological traits. We measured size of the body (forearm length and mass), ears, and wings for males and females. Ears and wings were significantly larger for bats in the mountains, suggesting that there is limited gene flow between populations despite their geographic proximity, and adaptation to differences in aridity or foraging habitat. However, body size was similar between environments, suggesting that either M. evotis possesses an ecologically flexible body type or that differences in extremity size are the result of environmentally induced phenotypic plasticity. Within environments, females were larger than males for all morphometrics. However, the degree of dimorphism was similar for mountain and prairie populations, indicating that dimorphism is not the result of different thermoregulatory needs in these populations.