Black rhino Diceros bicornis michaeli in Ngorongoro Crater, Tanzania were reduced by poaching from c. 110 animals in the mid 1960s to c. 20 by the mid 1970s. Despite little subsequent poaching the rhino population has not increased. This paper builds on a stakeholder workshop held in September 2003 to consider the problems facing these rhino and make recommendations for management. Research and monitoring is required as conservation decisions are, through necessity, being taken based on expert opinion. Genetic constraints may arise in the future given the small population size. We hypothesize, however, that the rhino population is currently limited by ecological factors including: neonatal predation by hyaena Crocuta crocuta, loss of calving refuges because of a reduction in Acacia xanthophloea, competition for browse with elephant Loxodonta africana and buffalo Syncerus caffer, tick-borne disease, and disturbance from tourism. These factors are exacerbated by an institutional philosophy of non-intervention. We suggest using adaptive inference to assess this hypothesis and to provide managers with appropriate information for rhino conservation.

An objective, non-invasive technique was developed for identifying individual black rhino from their footprints (spoor). Digital images were taken of left hind spoor from tracks (spoor pathways) of 15 known black rhino in Hwange National Park, Zimbabwe. Thirteen landmark points were manually placed on the spoor image and from them, using customized software, a total of 77 measurements (lengths and angles) were generated. These were subjected to discriminant and canonical analyses. Discriminant analysis of spoor measurements from all 15 known animals, employing the 30 measurements with the highest F-ratio values, gave very close agreement between assigned and predicted classification of spoor. For individual spoor, the accuracy of being assigned to the correct group varied from 87% to 95%. For individual tracks, the accuracy level was 88%. Canonical analyses were based on the centroid plot method, which does not require pre-assigned grouping of spoor or tracks. The first two canonical variables were used to generate a centroid plot with 95% confidence ellipses in the test space. The presence or absence of overlap between the ellipses of track pairs allowed the classification of the tracks. Using a new ‘reference centroid value’ technique, the level of accuracy was high (94%) when individual tracks were compared against whole sets (total number of spoor for each rhino) but low (35%) when tracks were compared against each other. Since tracks with fewer spoor were more likely to be misclassified, track sizes were then artificially increased by summing smaller tracks for the same rhino. The modified tracks in a pairwise comparison gave an accuracy of 93%. The advantages, limitations and practical applications of the spoor identification technique are discussed in relation to censusing and monitoring black rhino populations.

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.