Although fire is often incorporated into tallgrass prairie reconstructions, grazing by large, native herbivores typically is not. Little is known about how native grazers interact with plant communities during the reconstruction process, i.e. selection of plant communities in different stages of reconstruction, representation of exotic plant species in the diet, and the effect of abiotic features on habitat selection. We conducted a two-year (2006-07) diet and habitat selection study on reintroduced populations of elk (Cervus elaphus) and bison (Bos bison) at the Neal Smith National Wildlife Refuge near Prairie City, Iowa. This observational study included intensive surveys of native ungulate group locations throughout the summer seasons, estimation of percent cover of plant species in habitat patches, and collection of fecal samples for diet analysis. Bison and elk use of the reconstructed tallgrass prairie habitat was spatially nonrandom. Available cover, i.e. trees and reed canary grass (Phalaris arundinacea) patches, and farthest distance to fence influenced use of space by elk. Bison segregated into a bull group consisting of older bulls and a mixed sex/age group that included cows, yearlings, calves, and young bulls. The bison bull group appeared to avoid recently burned areas and selected for areas with a high grass:forb ratio and west-facing slopes. The mixed sex/age group was strongly attracted to the most recently burned patches and areas with a higher proportion of native plants. Bison diets consisted of >90% graminoids and elk used mostly forbs, >65%. Bison did not consume significantly different proportions of native species compared to exotic species, but elk diets consisted of > 80% exotic species in this ongoing tallgrass prairie reconstruction. Findings from this study illustrate the interactions of reconstruction activities and native grazers during the tallgrass prairie reconstruction process and should aid in future management plans in this greatly reduced ecosystem.