We assessed the utility of cranial measurements to discriminate between the western harvest mouse (Reithrodontomys megalotis) and plains harvest mouse (R. montanus). We tested four combinations of measurements using discriminant function analysis to determine if several measurements could be used together to identify individuals of the two species regardless of age. Individual cranial measurements could not be used to correctly identify all individuals of the two species when relative age was disregarded. When age was considered, adults and old adults, but not subadults, could be identified correctly based on univariate statistical data from cranial characters. All specimens of the two species, regardless of age, were identified correctly by discriminant function analysis using three of the four combinations of measurements
