African Vultures Don’t Follow Migratory Herds: Scavenger Habitat Use Is Not Mediated by Prey Abundance

Corinne J Kendall,Daniel I Rubenstein,Munir Z Virani,Keith L Bildstein,J Grant C Hopcraft,Matt Hayward

doi:10.1371/journal.pone.0083470

Corinne J Kendall, Daniel I Rubenstein + Show 4 more

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https://doi.org/10.1371/journal.pone.0083470

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Abstract

The ongoing global decline in vulture populations raises major conservation concerns, but little is known about the factors that mediate scavenger habitat use, in particular the importance of abundance of live prey versus prey mortality. We test this using data from the Serengeti-Mara ecosystem in East Africa. The two hypotheses that prey abundance or prey mortality are the main drivers of vulture habitat use provide alternative predictions. If vultures select areas based only on prey abundance, we expect tracked vultures to remain close to herds of migratory wildebeest regardless of season. However, if vultures select areas where mortality rates are greatest then we expect vultures to select the driest regions, where animals are more likely to die of starvation, and to be attracted to migratory wildebeest only during the dry season when wildebeest mortality is greatest. We used data from GSM-GPS transmitters to assess the relationship between three vulture species and migratory wildebeest in the Mara-Serengeti ecosystem. Results indicate that vultures preferentially cluster around migratory herds only during the dry season, when herds experience their highest mortality. Additionally during the wet season, Ruppell’s and Lappet-faced vultures select relatively dry areas, based on Normalized Difference Vegetation Index, whereas White-backed vultures preferred wetter areas during the wet season. Differences in habitat use among species may mediate coexistence in this scavenger guild. In general, our results suggest that prey abundance is not the primary driver of avian scavenger habitat use. The apparent reliance of vultures on non-migratory ungulates during the wet season has important conservation implications for vultures in light of on-going declines in non-migratory ungulate species and use of poisons in unprotected areas.

Highlights

The study of animal ecology has focused on herbivores, predators and parasites, and has largely overlooked scavengers [1]
Unlike herbivores, whose ecology is often governed by the interplay of predation risk and forage availability [2], [3], [4], or predators whose habitat use may be determined more by prey accessibility than abundance [5], [6], scavengers face a different set of challenges and their ecology is likely to be mediated by other ecological factors
Vulture habitat use is not driven by prey abundance Carcass availability is mediated by both prey abundance and prey mortality

Summary

Introduction

The study of animal ecology has focused on herbivores, predators and parasites, and has largely overlooked scavengers [1]. Foraging success for scavengers depends on their ability to search across large areas and rapidly detect carrion before it is decomposed by microbes or consumed by invertebrate and vertebrate competitors [9]. Because they generally experience limited predation, food availability, its predictability, and its accessibility have generally been found to be the key factors determining scavenger habitat use and distribution [10], [11], [12]. The relative importance of prey abundance and mortality and the interactions between these two factors, likely to shape habitat use in scavengers, have not been explored

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