An Overlooked External Character to Differentiate Myotis californicus and Myotis ciliolabrum (Vespertilionidae)

The observation of a perceived 4-mm tail extension beyond the border of the interfemoral membrane of the western small-footed myotis, Myotis ciliolabrum, and the absence of the free tail in the California myotis, Myotis californicus, stimulated a quantitative study to determine if the tail character could be verified as a consistent external criterion to differentiate these similar species. Existing study skins were unsuitable for this purpose, because the tail character had been destroyed or distorted by replacement of the tail vertebrae with wire. Twenty-three ciliolabrum and 22 californicus were collected in the Mojave Desert of California and prepared as study skins with tail vertebrae in situ. Examination of these specimens, identified by conventional methods, confirmed that the exserted tail was characteristic of ciliolabrum. Original descriptions, usually based on specimens preserved in alcohol, indicated that the tail character was recognized in ciliolabrum over a century ago.