Microhabitat use for five rodent species (Calomys musculinus, Calomys laucha, Akodon azarae, Oligoryzomys flavescens and Bolomys obscurus) inhabiting agroecosystems of the central Argentine pampa was investigated for 17 months at six mark-recapture grids. Thirteen vegetation variables were measured along 748 transects at trap stations where rodents were captured and 252 stations where no captures were made. Principal components analysis was used to describe physiognomic differences among crop and post-harvest habitats, as well as the less-disturbed borders of crop fields. Multiple logistic regression was used to assess the significance of principal components in predicting the presence of rodent species. Associations of rodents with plant species in border habitats were explored with Two-Way-Indicator-Species Analysis and correspondence analysis.

Aerial coverage by vegetation, as well as ground cover by litter, and graminoid species richness, were important variables in predicting the presence of all rodent species, except C. laucha. Vertical vegetation density and maximum height were also important in determining the presence of C. musculinus in soybean fields. Within border habitats, C. laucha was found in lower quality microhabitats (increased bare ground, decreased vegetative cover, and decreased vertical vegetation density) and was associated with the invasive, introduced grass, Cynodon dactylon. C. laucha was restricted to apparently sub-optimal areas within border habitats during periods of high rodent density. These data indicate subtle differences in rodent-plant associations among the members of the rodent assemblage and possible competitive exclusion of C. laucha from stable habitats.

Calomys musculinus is the principal reservoir for Junin virus, aetiological agent of Argentine haemorrhagic fever. These results have practical implications in helping define the risk of human disease on a fine scale and provide a theoretical basis for reservoir control and risk reduction.