The effect of variation in the spatial arrangement of plant tissues on the functional response of mammalian herbivores is one of the key parts of the foraging theory. In this study, 4 models for the intake rate of root voles (Microtus oeconomus) foraging in the pathes of fresh alfalfa (Medicago satival) leaves were evaluated. Each trial included observations of root voles in a single patch type, characterized by a different arrangement of leaf size and leaf density which represented spatially heterogeneous leaf patches. The size of the leaf offered to root voles was varied to control their bite mass, and plant spacing was varied to control leaf density within the patches. The composite model depicting the combined effects of bite mass and plant density fitted the data more properly than the other models. The maximal likelihood estimate of the parameters, Rmax, h and Vmax from the combined model represented the independent and direct estimates more closely than the other models. Although significantly linear regressive relationships existed between observed and predicted intake rates of root voles by the 4 models (P < 0.01), the composite model fitted best to the observations, indicating that the composite model described the dynamics of intake rates regulated by competing between foraging and walking of root voles. The composite model predicted a distance threshold (d*) distinguishing the mechanisms for functional responses: the vole′s intake rate was regulated by bite size when the leaf spacing was lower than the threshold, but once the leaf spacing exceeded the threshold, the vole′s intake rate was then regulated by the leaf density. The validating tests of these models provided a strong support to the hypotheses about intake rates to be regulated by dual mechanisms in small mammalian herbivores: the plant size regulated the intake rate of root voles in plant-abundant patches, while the plant density regulated their intake rates in plant-sparse patches.