The stable carbon isotope ratios in ostrich eggshell on known dirts or on natural vegetation in different parts of Cape Province, South Africa, are investigated. Results suggest that ostrich eggshell may be a more reliable material for radiocarbon dating than has been expected, more so than the inorganic fraction of bone. Measurement of the average ₁₃C/₁₂C ratio of the bird's plant diet can be used under defined circumstances to reconstruct the plant environment the bird lived in, particularly the nature and extent of the shrub cover. -- AATA