Standardising Home Range Studies for Improved Management of the Critically Endangered Black Rhinoceros

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.

Too Close and Too Far: Quantifying Black Rhino Displacement and Location Error During Research

“…When locating rhinos, we selected individuals at random without replacement until each of the 14 study animals had been located before selecting again from our rhino cohort (e.g. Plotz et al, 2016). For a direct sighting, we first determined the direction of each rhino's unique radio-transmitter signal from high elevations.…”

“…The subtropical vegetation varies from grasslands to Acacia spp. woodlands and denser thickets dominated by broadleaf genera like Euclea and Maytenus (Balfour & Howison, 2001;Plotz, 2014;Plotz et al, 2016).…”

“…Black Rhino Range Expansion Project, BRREP; Emslie, 2001;Linklater et al, 2012;Plotz, 2014;Hayward et al, 2017). Our experimental population consisted of 14 adult (>7 years; Law & Linklater, 2015) female rhinos who received horn-implanted radio transmitters (VHF) from March 2007 to October 2008 as part of a larger study of black rhino population dynamics (see Plotz & Linklater, 2009;Linklater et al, 2010a;Plotz, 2014;Plotz et al, 2016).…”

“…Descriptions of horn implant techniques and equipment are provided in Plotz et al (2016 Although the procedure to immobilize and insert horn-implant radio-transmitters could increase the sensitivity that rhinos may have towards humans, this is less likely in HiP because almost all individuals in the population are immobilized several times over their lives for reasons other than inserting horn-implant radio-transmitters (e.g. ear notches where ear tissue is removed to create unique patterns for identification purposes and the insertion of short-range transponders under the skin; Hitchins, 1990).…”

“…Researchers, therefore, continue to rely on hornimplant VHF radio transmitters (Pienaar & HallMartin, 1991;Shrader & Beauchamp, 2001) for regular monitoring of black rhinos as they have proved to be robust to the challenges of rhinos and their habitat (e.g. Morgan, Mackey & Slotow 2009;Göttert, Schöne, Zinner, Hodges & Böer, 2010;Odendaal-Holmes, Marshall & Parrini, 2014;Plotz, Grecian, Kerley & Linklater, 2016).…”