Spatially explicit poisoning risk affects survival rates of an obligate scavenger

A Monadjem,A Kane,C Murn,C Kelly,A Botha

doi:10.1038/s41598-018-22632-y

Abstract

Obligate scavengers such as vultures provide critical ecosystem services and their populations have undergone severe declines in Asia and Africa. Intentional poisoning is a major threat to vultures in Africa, yet the impact on vulture populations of where poisoned carcasses are positioned is not known. We used re-sightings of 183 African white-backed vultures captured and tagged in two regions of South Africa, some 200 km apart, to estimate spatial differences in relative survival rates across life stages. Juvenile survival rates were similar in the two regions, whilst subadult and adult survival rates differed significantly. Using agent-based modelling, we show that this pattern of relative survival rates is consistent between regions that differ in intensity of poisoning, despite the proximity of the two regions. This may have important consequences for vulture conservation and the targeting of conservation efforts, particularly with regard to the efficacy of “vulture safe zones” around vulture breeding populations.

Highlights

As the only obligate avian scavengers, vultures are important for ecosystem health and functioning[1,2,3], yet their populations have been severely depleted by a variety of factors that include poisoning, electrocution by power infrastructure, and large-scale modifications to the landscape[1,4,5,6]
This study reported that in six of seven scenarios the population declined and in two cases the population was extirpated in 50–60 years[21], highlighting that vulture populations are extremely susceptible to poisoning-induced mortality
183 African white-backed vultures were fitted with patagial tags, of which 104 birds were captured in KwaZulu-Natal and 79 in the Greater Kruger National Park

Summary

Introduction

As the only obligate avian scavengers, vultures are important for ecosystem health and functioning[1,2,3], yet their populations have been severely depleted by a variety of factors that include poisoning (toxicosis), electrocution by power infrastructure, and large-scale modifications to the landscape[1,4,5,6]. Green et al developed a demographic model to show that even a small proportion of carcasses contaminated with nonsteroidal anti-inflammatory drugs was sufficient to explain the catastrophic decline of vultures on the Indian sub-continent[8] This model was not spatially explicit, in that the authors did not include “location” (of poisoned carcasses) as a feature in the model but rather assumed that the distribution of these carcasses would be spatially homogenous. Understanding spatially variable impact of poisoning is important because areas that are vital for vulture conservation (such as breeding colonies, for example) might be at a higher risk; identifying these spatially explicit risks is a priority

Methods

Results

Conclusion