Estimating population parameters of African elephants: a photographic mark-recapture application in a South African protected area

Accurate estimates of demographic parameters are instrumental in effective management of animal populations. For species with individually distinctive features, photo-identification (photo-ID) provides a reliable means to gather capture–recapture data for population parameter estimation with considerable precision and accuracy. We use a 3-year photo-ID mark-recapture dataset of African savannah elephants (Loxodontaafricana) in Pilanesberg National Park (PNP), South Africa, to model their population size and estimate survival rates. All photographed elephants, irrespective of age, were individually identified based on their unique pattern of facial wrinkles. The population currently numbers 385 elephants (95% CI = 380–401), of which nearly half are grown individuals in a sex ratio of 1 male: 1.23 female. Considerable heterogeneity in capture and recapture probabilities, both within and between sex-age classes suggests some form of individual-specific or herd-specific variability, perhaps behavioural or spatio-behavioural dissimilarity within the PNP population. Estimated annual survival rates are high (0.967–0.996) and do not differ between sex-age classes, a likely expression of an extended parental care, low predation pressure, access to rich food and water resources, and absence of targeted killing/poaching. The lack of detectable difference between sexes in adult survival/mortality sets PNP elephants apart from other known African elephant populations and warrants further research attention. Given previous estimates (aerial counts in the early 2000s), the PNP elephant population has grown ~ 5.7% per annum over a 16-year period. This is similar to what is reported in other conservation areas in South Africa, but considerably lower than previously projected. Natural mortality, even if low as 0.4–3.3%, is not negligible and plays a role in moderating population growth. This realisation must be recognised when considering population management measures. It is, therefore, important to obtain and apply the most up-to-date population-specific demographic parameters when making management decisions. Periodic photo-ID surveys with mark-recapture analyses can generate such demographic indicators with a considerable accuracy and should be adopted as a useful tool to inform management decisions, complimentary to direct aerial counts, especially in small-to-medium size fenced conservation areas.