In Mesa Verde, _P. maniculatus_ inhabits the more arid, open areas. When the population is dense, individuals of this species are found also in pinyon-juniper woodland. Apparently _P. maniculatus_ prefers the grassy areas and the thickets of oak brush. Although such habitats have harsh climatic conditions, they offer innumerable hiding places, and thus have great advantage for a species confined to the ground. The low requirements of water per gram of body weight, the ability to eat diversified foods, the use of varied habitats, the high fecundity, and the ability to use any nook for retreat or nesting make _P. maniculatus_ a successful inhabitant of most parts of Mesa Verde, and indeed, of most of North America. LITERATURE CITED ANDERSON, S. 1961. Mammals of Mesa Verde National Park, Colorado. Univ. Kansas Publ., Mus. Nat. Hist., 14:29-67, 2 pls., 3 figs. ARRHENIUS, G., and E. BONATTI 1965. The Mesa Verde loess, pp. 92-100, _in_ Contributions of the Wetherill Mesa Archeological Project, Memoirs Soc. Amer. Archeol., 19; American Antiquity, 31, No. 2, Pt. 2. ASDELL, S. A. 1964. Patterns of mammalian reproduction. Comstock Publ. Co., Ithaca, viii + 1-670 pp. BAILEY, V. 1931. Mammals of New Mexico. N. Amer. Fauna, 53:1-412, 22 pls., 58 figs. BEIDLEMAN, R. G. 1954. October breeding of _Peromyscus_ in north central Colorado. Jour. Mamm., 35:118. BRUSVEN, M. A., and G. B. MULKERN 1960. The use of epidermal characteristics for the identification of plants recovered in fragmentary condition from the crops of grasshoppers. North Dakota Agricultural Exp. Sta., Fargo, Research Rept., 3:3-11. BURT, W. H. 1940. Territorial behavior and populations of some small mammals in southern Michigan. Misc. Publ. Mus. Zool., Univ. Michigan, 45: 1-58, 2 pls. CALHOUN, J. B., ed. 1948-1956. Annual reports of the North American census of small mammals. Distributed by the editor, National Institutes of Health, Bethesda 14, Maryland. 1959. Population dynamics of vertebrates release No. 10, Revised sampling procedure for the North American census of small mammals (NACSM). pp. 1-12, Distributed by the editor, Nat. Inst. Health, Bethesda 14, Maryland. CHEW, R. M. 1951. The water exchanges of some small mammals. Ecological Monographs, 21:215-225. 1965. Water metabolism of mammals, pp. 43-178, _in_ Physiological Mammology Vol. II Mammalian reactions to stressful environments, Mayer, W. V., and R. G. Van Gelder, eds., Academic Press, New York, xii + 1-326 pp. COGSHALL, A. S. 1928. Food habits of deer mice of the genus _Peromyscus_ in captivity. Jour. Mamm., 9:217-221. COLLINS, H. H.