Power-line related mortalities of the Cape Vulture (Gyps coprotheres) within the Eastern Cape, South Africa: modelling terrain characteristics in hotspot areas using GIS

Abstract

This study examines and correlates basic terrain and topographic characteristics at power line incident hotspots of Cape Vulture (Gyps coprotheres) within the Eastern Cape, South Africa. The Cape Vulture (G. coprotheres) is a threatened endemic Southern African Vulture. Each year, its population is further threatened by collisions and electrocutions on power line infrastructure that crisscross across South Africa. Each documented collision and electrocution incident is recorded into a national database and recommended mitigation measures are implemented to prevent further loss at these various problematic sites in a reactionary manner. Every day vulture flight patterns overlap the extensive power line network, and yet collisions and electrocutions are only recorded in certain areas.

This study uses the spatial frequency distribution of Cape Vulture power line incident data from the Eastern Cape in South Africa to identify areas of higher frequency, also known as hotspots, across the province. Exploratory Spatial Data Analysis (ESDA) revealed that the majority of the vultures are electrocuted and that the number of birds affected in a single electrocution incident is higher than those affected in a single collision incident. Larger transmission power lines are intrinsically associated with collision incidents and smaller distribution lines with electrocution incidents.

Avian power line risks are a combination of biological, technical and topographical and climatic factors. This study focuses on the GIS modelling of terrain and topographical factors at each collision and electrocution hotspot, which were then compared across hotspots to check for correlation. Unfortunately, distinct terrain characteristics signatures for elevation, slope and aspect and curvatures were not identified but instead displayed similar quantifiable characteristics. Other attributes such as vegetation cover, water, roost and restaurant proximities, line orientation to wind directions and visibility at each hotspot were more distinct and could be correlated across hotspots. These characteristics were organised into a set of rules that would guide the further development of a predictive model, which can be used to assess the remainder of the Eastern Cape where there is an under-representation of the incident data. It is anticipated that this study’s results will be valuable to the Cape Vulture non-governmental organisations (NGO’s) and Eskom to inform proactive mitigation action to reduce or avoid further collision and electrocution of these endangered birds.