We used a bird and mammal exclosure design on plowed ground to test for the effects of granivory and herbivory by small vertebrates on early stages of tallgrass prairie succession. Seed predation by birds and browsing by rodents had major and additive impacts. In high- and low-density plantings, respectively, seed-eating birds reduced plant densities by 20% and 23% and grass biomass by 24% and 34%. Meadow voles did not affect plant numbers but reduced forb biomass by 35% in high- and 57% in low-density plantings. In high- and low-density plots, respectively, birds reduced species richness by 3% and 17% without influencing diversity; selective browsing by voles on two legumes and one coneflower left species number unaffected but reduced diversity by 4% and 25% by accentuating dominance of already-prominent species. Bird effects were more pronounced in high-density plantings, while vole effects were most pronounced in low-density plantings. Results suggest that opportunistic finches and doves that seek out high seed concentrations depress tallgrass plant densities on open ground, while voles, which selectively forage on emerging vegetation, alter community structure, especially when their home ranges include low-density plant assemblages. Both results are likely to be relevant to native prairies after burns or other disturbance, and to ecological restoration. Key words: birds, seed predation by; diversity; experimental restoration; field experiment; foraging theory; granivory; herbivory; rodent browsing; tallgrass community, revegetation: tallgrass plantings, small vertebrate effects on; tallgrass prairie, composition and diversity: vole herbivory., INTRODUCTION Do small vertebrates influence composition and diversity of tallgrass prairies? The question is important because tallgrass remnants on fertile, well-watered soils represent North America's 'most endangered' major ecosystem (Noss [...] more...