Productivity of herbivores depends on their success in attaining protein and fat stores above survival and reproductive thresholds. Populations in semi-arid regions depend on mobility to access resources that are spatiotemporally heterogeneous. The potentially isolated wildebeest (Connochaetes taurinus), gemsbok (Oryx gazelle) and springbok (Antidorcus marsupialis) populations in the Central Kalahari Game Reserve (CKGR) depend on high-quality grasslands, a limited and important vegetation type. We used microhistological analyses of dung samples from these ungulates to estimate their seasonal diet composition. Results showed that forage quality and availability drive wet season diet composition. Protein-rich short grasses on pans were important for all ungulates in the wet season. Wildebeest, gemsbok and springbok diets overlapped in the wet season. The favoured grasses were depleted during the dry season and the ungulates shifted their diet likely as an adaptive mechanism to maintain intake rates. Wildebeest fed on lower-quality grasses while springbok and gemsbok fed on dicotyledons when more preferred forage was scarce. Our findings demonstrate the importance of access to heterogeneity of vegetation types that provide high-quality resources in the wet season (saline pan grassland habitats) and dry season reserves of forage (woodland habitats).