Obtaining longitudinal data about the feeding ecology of long-lived iteroparous mammals is rare, but enhances our understanding of how the environment influences niche breadth and dietary diversity within a species. We analysed forty years of feeding records obtained from a population of Thornicroft’s giraffes (Giraffa camelopardalis thornicrofti) living in the Luangwa Valley, Zambia. Giraffes are browsers that have been reported to feed primarily upon Acacia leaves, but their feeding ecology in some locations conflict with this interpretation. Giraffes in the