Using high-resolution remote-sensing to quantify nest site characteristics of white-backed vulture (Gyps africanus) in Karingani Game Reserve, Mozambique

Abstract

he decline of White-backed Vultures (WbVs), a critically endangered species, in southern Africa calls for urgent intervention and an increased understanding of their nesting requirements to improve conservation of suitable nesting trees. There is currently little research on the nesting preferences of WbVs, and few measurements on how variation in individual tree architectures or the surrounding area influences WbV nest site selection. Moreover, current methods of tree measurement are time-consuming, susceptible to inaccuracy due to human error, and potentially dangerous. This study aimed to fill these critical knowledge gaps by combining remotely sensed Light Detection and Ranging (LiDAR) data and Red-Green-Blue (RGB) imagery with helicopter surveys of nest locations (n=30) to explore nest site selection of WbVs in Karingani Game Reserve (KGR), Mozambique. The LiDAR and RGB orthomosaics allowed for precise and accurate measurement of various tree-level characteristics: canopy height, canopy area, canopy roughness, nest orientation and peripheral position, and distance to water. Surrounding vegetation cover was also measured, along with surrounding canopy height, and vegetation roughness within 100 m of nesting trees. A Resource Selection Function (RSF) analysis was used to determine which variables WbVs favoured when selecting a nesting tree. This study found that WbVs in KGR prefer nesting in trees with an average height of 14 m (10.58 m - 16.34 m), with large variation and roughness within their canopy (4.04s), and large canopy area, averaging 161.58m². White-backed Vultures in KGR were found to position their nests on the northern side of the tree, but with no preference for nest position in relation to canopy edge. The approach of using LiDAR and RGB imagery was found to be effective for measuring tree-level variables in a time-effective and accurate manner, while revealing more information on the nesting ecology of WbVs in KGR. This approach allowed us to gain a better understanding of the specific requirements of WbVs when selecting a tree to nest in, and thus aid protected area management by providing valuable information regarding the need to conserve specific habitats within protected areas to ensure the survival of this species. This novel approach could become the new standard for measuring trees for large raptor studies, allowing researchers to collect data from much larger areas and increased sample sizes with ease.