Multiple GPS fix intervals show variations in the manner African White-backed Vultures Gyps africanus utilise space

Abstract

ABSTRACT Application of spatial data is becoming increasingly important as a tool for mapping and understanding space utilisation patterns especially for critically endangered species. In this study, we tested how variation in the GPS fix interval may influence space utilisation patterns by African White-backed Vultures in Hwange National Park and the surrounding areas. In order to test our objectives, we collected data from six African White-backed Vultures using solar powered GPS-GSM units. The data were collected for periods ranging from five months to nineteen months (28 June 2016 to 30 January 2018), resulting in 89 809 total GPS fixes. We tested whether home range and core areas estimated at different fix interval differ significantly. We also tested whether African White-backed Vultures show significant site fidelity and at what sampling frequency the estimated home ranges tend to reach an asymptote. We used total individual data and seasonal data to test these hypotheses. In order to estimate home range size at different fix intervals, we used the Brownian Bridge Movement Model, because unlike other traditional estimators, it explicitly incorporates temporal sequence in GPS fixes, accounts for autocorrelation in movement data, as well as missing GPS data. Home range estimates differed significantly at different GPS fix intervals. Home range and core areas for five vultures were concentrated within conservation areas. African White-backed Vultures also showed significant site fidelity across seasons except for vulture three, which demonstrated nomadic tendencies. Results on home range asymptote were not conclusive, because of unique individual vulture space use patterns at different fix intervals. Our study was the first to track and monitor space utilisation patterns by mature African White-backed Vultures in the Hwange ecosystem. Accordingly, our results have critical conservation implications for the wide-ranging, critically endangered species.