Densities and Habitat Preferences Exhibited by Peromyscus Maniculated and Sigmodon Hispidus in a Mixed Grassland

The population densities, habitat preferences, and importance values of Peromyscus maniculatus nebrascensis (Coues) and Sigmodon hispidus texianus (Audubon and Bachman) in a 13.57 acre relict grassland 1.5 miles southwest of Hays, Ellis County, Kansas were studied from April, 1965 to March, 1967. Calculations were made utilizing electronic data processing with a 20K 1620 IBM computer. The calculations of population densities for the study area were compared using four methods: Lincoln, Schnabel, Schumacher-Eschmeyer, and actual numbers. Ecological densities, the density per acre per habitat, were used as a measure of the species' habitat preferences. Importance values, relative density plus relative frequency, were calculated and compared. A comparison of methods used to estimate population densities indicated that: the actual number of mammals marked during the 14-day trapping periods was the most reliable; the Lincoln index, the least conservative method, was erratic on a day to day basis but more reliable when used over a longer period, and the Schnabel and the Schumacher-Eschmeyer estimates, conservative in nature, allowed for accumulation of captures and recaptures over the trapping periods, thus making the daily and final estimates smooth . The densities of Peromyscus for the entire study area ranged from 7.3 per acre to 1.2 per acre, while densities of Sigmodon ranged from 6.4 per acre to 0.07 per acre. A larger number of males than females was indicated for both species. The ecological density indicated that the most preferred habitats were mixed grass for Peromyscus and weed for Sigmodon. Other preferences were ranked. The magnitude of the importance values served as an indicator of the relative importance of a species when compared to all other species within or between communities. This was most functional on a month to month basis.