Too close and too far: quantifying black rhino displacement and location error during research

Observer impacts on animal behaviour concern conservation managers and researchers of critically endangered species, like black rhino (Diceros bicornis). Repeated observations are sometimes necessary, but may distress and displace animals. Information from more remote observations using radio-triangulation is limited and includes larger measurement errors. We investigated the influence of observer visits on average daily displacement by 14 black rhinos in Hluhluwe-iMfolozi Park, South Africa, and the accuracy of triangulated locations with increasing observer distance and the time to complete bearing sets. Fortnightly observer visits for 34 months that often disturbed rhino (52% of visits) had an insignificant impact on daily movements. However, increasing observer distance from rhino, and the time taken to triangulate, were both significant explanations of rhino location error. We recommend that measures to quantify and minimize observer influence become standard monitoring protocol and that bearings for radio-triangulation of black rhino locations occur from <1 km (not >2 km), and be completed within 30 minutes. Reporting measures for spatial error and observer influence permit the development of objective thresholds for data inclusion to improve radio-telemetry data and inter-study comparisons of black rhino range studies.