Systematics of the Northern Grasshopper Mouse (Onychomys Leucogaster) on the Central Great Plains

Systematic relationships of populations of the northern grasshopper mouse, Onychomys leucogaster, on the central Great Plains are assessed based on study of molts and pelages and on morphometric analyses. Variation in color of any one population of Onychomys on the central plains reflects differences in three developmental pelages, with two intervening, maturational molts, and one annual molt and pelage. Geographic variation in color of pelage is clinal, the dorsum gradually changing from pale in the west to darker in the east, whereas variation in mensural characters is slight and not entirely coincident with that of pelage. Two nominal subspecies of O. leucogaster, O. 1. arcticeps Rhoads to the west and O. 1. breviauritus Hollister to the east, have been recognized on the central Great Plains. These two taxa herein are regarded as synonymous, with the name O. 1. arcticeps having priority. Populations in Moffat and Jackson counties in the intermontane region of northwestern Colorado, currently recognized as pertaining to the plains taxon O. 1. arcticeps, are reassigned to the Great Basin subspecies, O. 1. Brevicaudus Merriam. Populations inhabiting the Missouri lowlands of northeastern Nebraska (herein referred to O. 1. arcticepts possibly should be reassigned to O. 1. leucogaster (Wied-Neuwied), but additional data are needed to substantiate this hypothesis.