Black rhinoceros demography should be stage, not age, based.

Biologically meaningful and standardized definitions of life stages are essential for demographic studies, especially for endangered and intensively managed species such as rhinoceros. Focusing on the black rhinoceros Diceros bicornis, we argue that standardized biological definitions of calf, subadult, and adult, rather than age classes, provide the appropriate basis for black rhinoceros demography. Age classes do not correlate well with the risks of mortality nor characterize, at least for females, the attainment of reproductive maturity. Black rhinoceros demography based on age classes, typical of existing literature, obscures the significance of studies of mortality and fecundity. Compar