Small Mammals of a Dry-Land Cropland in Western Kansas

Small mammal populations in cropland in Ellis County, Kansas, were studied throughout the three year dry-land farming rotation of winter wheat, grain sorghum, and summer fallow commonly practiced in that area. Small mammal populations in the cropland were compared with those in a nearby, relict mixed-grass prairie. Seven species of small mammals were captured in the cropland, but only P. maniculatus was resident year-round; the population of P. maniculatus in the cropland was stable and was larger than that in the relict area. Small mammal populations were compared among four crop phases--wheat stubble, grain sorghum, sorghum stubble, and wheat-- and were found to be similar in diversity of mammals and almost identical in species composition and relative abundance. In only two instances did farming practices seem to influence the sizes of populations present: the grain sorghum and sorghum stubble phases might have been less stable than the other phases as shown by a higher turnover rate of mammals in those phases. Relatively few ecological studies of small mammals have dealt with croplands as habitat, and most of those have focused on the effects of the small mammals on crops and the best methods to control those responsible for crop damage (see Fleharty and Navo, 1983, and Navo and Fleharty, 1983, for literature summary). However, Fleharty and Navo (1983) asserted that questions about the effect of the cropland on small mammal populations are equally important. Do certain crops proscribe particular species of small mammals? Do particular species prefer one crop over another? Do certain farming practices favor some species or affect all in the same manner? Is colonization of a cropland dependent on the availability of a reservoir of species that are generalists, or can more specialized species establish populations? In west-central Kansas, a common regimen of dry land farming is to plant winter wheat in autumn, harvest it the next summer, plant grain sorghum the following spring, and harvest that in the autumn. The field then is left fallow through the following spring and summer and again is planted to winter wheat in autumn, thus completing a three- year rotation. Navo and Fleharty (1983) simultaneously trapped animals in a wheat field and a grain sorghum field for approximately 1 year and compared the results to a nearby, ungrazed grassland. No trapping was done for any length of time when the fields lay fallow in either wheat or sorghum stubble. The purpose of this study was to trap small mammals from a cropland as it progressed through the three-year rotation of wheat, grain sorghum, and stubble phases to estimate (1) which species of small mammal utilize the site, (2) the relative sizes and demographic structure of populations present, and (3) the effects that change in crop phase and agricultural perturbations have on the species that utilize the site.