Populations of Small Mammals in North-Central Oklahoma

Abstract

Populations of small mammals were assessed in six major habitat types (moderately and heavily grazed grasslands, lowland and upland forests, cropland, and prairie relic) in north-central Oklahoma using four grids of live traps and 26 traplines. Animals were sampled during March, May, and August of 1975, with a total of 23,280 trap-nights in the grid analysis and 1,699 on the lines. Five to eight species were captured in both the grassland and woodland habitats. Population densities were higher in March than in May or August. For the moderately grazed grassland, total small mammal density in March was 8.4 animals/ha, with deer mice (Peromyscus maniculatus) predominant (3.2/ha); total density in May was 4.2/ha (deer mice, 0.7); and 0.9 (no deer mice) in August. Comparable values for the heavily grazed grassland were: March, 8.8/ha (6.4); May, 4.8 (1.2); and August, 5.9 (1.5). Densities in the lowland forest were considerably higher and white-footed mice (P. leucopus) were most abundant. Total densities (and those for white-footed mice) were: March, 35.4/ha (34.5); May, 20.6 (18.1); and August, 20.8 (13.6). Estimates for the upland forest were: March, 24.3/ha (23.4); May, 14.8 (9.7); and August, 13.7 (18.9). Species composition in the prairie relic was similar to that for the other grasslands. White-footed mice and hispid cotton rats (Sigmodon hispidus) were the most common forms in croplands. Survivorship, as indicated by recapture in subsequent sampling periods, was higher for white-footed mice than for deer mice. Apparently prairie voles (Microtus ochrogaster), which were found in relatively low numbers, do not exhibit marked population cycles on the site, while white- footed and deer mice undergo substantial population fluctuations. Species with western continental distributions were restricted to grasslands, while eastern forms were found primarily in the wooded areas of the study site. The mammalian fauna of Oklahoma has received attention from biologists for the past four decades, although no recent comprehensive treatment is available. Blair and Hubbell (1938) and Blair (1939) described faunal relationships of biotic districts in the state, and various investigators have conducted ecological studies involving single species. A few areas have been studied in detail. Blair (1938)