Monitoring survival probabilities of Cape Vultures Gyps coprotheres in South Africa, using GPS tracking data

Abstract

The Cape Vulture Gyps coprotheres is a species of Old-World vulture endemic to southern Africa. Currently listed as ‘Vulnerable’ by the IUCN, they face increasing threats from anthropogenic hazards, such as collisions with man-made infrastructure and poisoning events, leading to ongoing population declines. This study aimed to investigate the survival probabilities of a sample of 20 Cape Vultures, fitted with GPS tracking devices whilst fledglings at the Skeerpoort breeding colony, in the Northwest province of South Africa. These individuals were then monitored for a period of 1 683 days, with a known fate index created to track any deaths or removal from the population, allowing for both cumulative and annual estimated survival rates to be calculated. Cumulative survival probability decreased from 0.512 at one year to 0.171 by year four, with 64% of all confirmed mortalities occurring within the first year and electrocution and collisions with power lines being the most prevalent causes (accounting for 20% and 15% of all outcomes respectively). Whilst annual survival probabilities appeared more stable, 0.512 in the first year and 0.540 in the fourth, these survival rates are markedly lower in comparison to those of other studies on Cape Vultures, as well as other vulture species and, furthermore, an extrapolated model for future survival predicted a survival probability of just 0.014 ten years after the GPS device was fitted. These findings highlight the need for targeted conservation measures, such as improved power line management and supplementary feeding stations to reduce mortality during the juvenile and subadult life stages of Cape Vultures.