Abstract
Comparisons of recent estimations of home range sizes for the critically endangered black rhinoceros in Hluhluwe-iMfolozi Park (HiP), South Africa, with historical estimates led reports of a substantial (54%) increase, attributed to over-stocking and habitat deterioration that has far-reaching implications for rhino conservation. Other reports, however, suggest the increase is more likely an artefact caused by applying various home range estimators to non-standardised datasets. We collected 1939 locations of 25 black rhino over six years (2004–2009) to estimate annual home ranges and evaluate the hypothesis that they have increased in size. A minimum of 30 and 25 locations were required for accurate 95% MCP estimation of home range of adult rhinos, during the dry and wet seasons respectively. Forty and 55 locations were required for adult female and male annual MCP home ranges, respectively, and 30 locations were necessary for estimating 90% bivariate kernel home ranges accurately. Average annual 95% bivariate kernel home ranges were 20.4 ± 1.2 km2, 53 ±1.9% larger than 95% MCP ranges (9.8 km2 ± 0.9). When home range techniques used during the late-1960s in HiP were applied to our dataset, estimates were similar, indicating that ranges have not changed substantially in 50 years. Inaccurate, non-standardised, home range estimates and their comparison have the potential to mislead black rhino population management. We recommend that more care be taken to collect adequate numbers of rhino locations within standardized time periods (i.e., season or year) and that the comparison of home ranges estimated using dissimilar procedures be avoided. Home range studies of black rhino have been data deficient and procedurally inconsistent. Standardisation of methods is required.
Highlights
Accurate home range estimates are important because they provide insight into the ecological needs of an organism and the spatial structure of populations [1]
In Hluhluwe-iMfolozi Park (HiP), an alleged 54% increase in black rhino home range estimates in different studies from 1991 to 2001 ([7]cf. [8]) was used as evidence for deteriorating habitat quality and over-population [8]; but the home ranges in each study were calculated using different methods, with differing number of rhino locations collected over varying periods of time
The historical sequence of home range size estimates for black rhino in HiP have been used to conclude that their habitat is deteriorating and the reserve over-populated because home ranges sizes have increased [8, 47]
Summary
Accurate home range estimates are important because they provide insight into the ecological needs of an organism and the spatial structure of populations [1]. The reliability of home range size estimates and their usefulness as a conservation tool has been eroded by the tendency for studies to ignore minimal data requirements and use dissimilar techniques that prevent meaningful inter-study comparisons [2, 3]. Home range size has been an important part of management decision-making for the critically endangered black rhinoceros [5], but studies (n = 24) have been plagued by data deficiencies, undescribed methodological detail and inconsistent estimations of home ranges (S1 Table, [3, 6]). The historical home range estimates for black rhino in Hluhluwe-iMfolozi Park (HiP), South Africa (Table 1), illustrates these procedural inconsistencies and the potential for home range studies to mislead conservation management [3]. Standardisation guidelines for black rhino home range studies are required
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