Summary: A 6.1-acre rectangle in ungrazed and unburned tall-grass prairie at Camp Bullis, Bexar County, Texas, was live-trapped from August 4 through 12, 1947. The home range of SIgmodon hispidus in this habitat was less than 100 feet in diameter for females, and less than 200 feet for males. Greater travels were recorded only for two males. The home range of Baiomys taylori was less than 100 feet in diameter for both sexes. None was taken in traps more than 86 feet apart. The population size was calculated by using the collection ratio to estimate the total number using the area. This total was converted to per acre figures by treating it as the population of the study area plus an area around it equal in width to one-half home range diameter. For this purpose, minimal and maximal estimates of the home range size were used. The resulting figures provide limits between which the true number per acre is believed to fall. The population of Sigmodon was found to be 10 to 12 per acre. The Baiomys population was estimated to be 6 to 8 per acre. A sudden large increase in the number of unmarked Baiomys occurred during the trapping period. Possible explanations for the increase are discussed. Runways were very poorly defined. When found, they could be traced for only a few feet. Sigmodon and Baiomys were common in unburned tall-grass prairie that had a mat of dead grass, but were rare in burned prairie that was nearly identical except for the absence of the dead grass mat. It is suggested, that the low populations of small mammals on the eastern portion of the Edwards Plateau can be explained in part by two factors: 1) elimination of the grass mat by grazing, or, as at Camp Bullis, by annual burning; 2) the firmness and toughness of the stony clay soil. This may account for the scarcity or absence of burrowing rodents, including most geomyids and heteromyids.
Additional publication details
A Sigmodon and Baiomys population in ungrazed and unburned Texas prairie