Natural History and Karyology of the Yucatán Vesper Mouse, Otonyctomys hatti

eventeen specimens of the rare Yucatan vesper mouse, Otonyctomys hatti, are now known from Belize, Guatemala, and the Mexican states of Campeche, Quintana Roo, and Yucatan. We herein report a second specimen of O.hatti, from Belize, extending the known geographic range of the species 95 km te the southeast in the country. This is the first location at which O. hatti has been taken sympatrically with the Central American vesper mouse, Nyctomys sumichrasti. We also report data on three additional specimens of 0. haui from Campeche. yctomys and Otonyctomys share similar habits and habitat requirements, and might compete where they overlap. However, the distribution of 0. haui corresponds closely to that of other Yucatan endemic, and the distinct distributions of the two genera probably reflects biogeographic history and different habitat requirements, rather than result from direct competition. The karyotype of 0. haui is 2n=50, F =58. Although superficially similar, it differs in important respects with the karyotypes reported for N. sumichrasti.