Dietary habits of the common rodents in an agroecosystem in Argentina

Dietary habits of five common rodents in agroecosystems on the central Arge ntine Pampa were studied for 15 months using microhistological analysis of stomach contents. All five rodent species were omnivorous, but proportions of major dietary items (arthropods, dicot leaves and seeds, monocot leaves and seeds) varied among species and seasons. Akodon azarae largely was ento mophagous; arthropods formed 41-62% of the diet in all seasons. The other f our species (Calomys musculinus, Calomys laucha, Bolomys obscurus, and Olig oryzomys flavescens) consumed most diet items throughout the year, but rela tive proportions varied among seasons. Leaves formed a relatively minor pro portion of the diet (12-16% overall for all species) throughout the year. A ll species except A. azarae consumed higher quantities of seeds (50-73% of stomach volume) than arthropods (15-35%) during autumn and winter but switc hed to higher quantities of arthropods (30-53%) in spring and summer. Diet breadth was narrower and overlap generally highest during winter when all s pecies were forced to subsist on a reduced set of available resources. Of 2 8 plant species with >2% cover in the environment, 25 were identified in st omachs of one or more of the five rodent species. The most important plant species in the diet were corn and soybeans (mostly grain), seed of Johnson grass (Sorghum halepense), chickweed (Stellaria media), and Amaranthus. Hig h consumption of arthropods, especially by A. azarae, contraindicates the b road-scale use of rodenticides until the role of that rodent species in the control of pest insects can be ascertained.