We compared the grass height grazed by white rhino, wildebeest, zebra and impala through the dry season months in the Hluhluwe–iMfolozi Park in South Africa. We expected that the grass height grazed would increase with the body size of the herbivore species, as suggested from past studies of resource partitioning among large mammalian herbivores. Instead we found that the largest of these species, white rhino, concentrated on the shortest grass, while the smallest species, impala, grazed heights intermediate between those grazed by wildebeest and zebra. Results suggest that the scaling of mouth width relative to body size, and hence to metabolic demands, may be the primary factor governing grass height selection, rather than body size alone. This calls into question the widespread assumption that smaller herbivores are superior competitors through being able to persist on sparser vegetation. Furthermore, there was considerable overlap in grass height grazed among these four species, indicating that niche separation by grass height is inadequate alone to explain their coexistence.