Effects of immobilization on fertility in female black rhino (Diceros bicornis)

Forty-six female black rhino were immobilized 113 times in the Sinamatella Intensive Protection Zone, Zimbabwe, from August 1992 to October 1997. The effects of immobilization on inter-calving interval (ICI), calving rate (calves/female/year), conception and calves born/year were assessed. The mean ICI (n=17) was 40.24+/-4.96 months. There was a significant linear relationship between the number and interval of immobilizations in the preconception interval (PCI) and duration of ICI; further investigations were made to overcome possible effects of temporal autocorrelation. Both a non-linear model and a general linear model (with five independent effects) showed a significant relationship only between the ICI and mean immobilization interval in the pre-conception interval (PCI), but not the mean immobilization interval in the whole ICI (including gestation immobilizations). Both suggested that the relationship between immobilization and inter-calving interval was not the result of temporal autocorrelation and that the immobilization regime significantly affected the ICI. Using the calving rate as a response variable, five effects were tested in a general linear model. Only the immobilization rate in the PCI was significant. For conceptions per calendar month, we examined two effects in a general linear model: the number of mature females immobilized each month, and rainfall in the month of conception plus 2 previous months. Both effects were significant. For the number of calves born/year, the effect of the immobilization regime (the number of mature females immobilized/year) and rainfall were examined. Only immobilization was significant. We suggest that the unusually intensive immobilization regime undertaken at Sinamatella has negatively impacted on female fertility, and discuss possible mechanisms. We also suggest the need to adopt guidelines to minimize the impact of immobilization on fertility in female black rhino.