Wild and hand-reared Cape Vulture Gyps coprotheres nestlings were monitored during two breeding seasons in 1981 and 1982. Growth and behavioural development were examined, and changes in body mass were related to changes in body water and fat reserves. There was no significant difference between growth-rates of body mass and of wing length for hand-reared and wild nestlings. Body water was correlated with body mass (r2 = 0,995), and fat-free body mass was correlated with body water (r2 = 0,999) during growth, thus providing estimates of fat reserves in wild nestlings Growth followed. a sigmoid pattern determined by the consistent deposition of body constituents, with body mass at any given age proximally determined by fluctuations in body water and fat reserves, and ultimately determined by variations in food provisioning.