How Predictability of Feeding Patches Affects Home Range and Foraging Habitat Selection in Avian Social Scavengers?

Sophie Monsarrat,Carmen Bessa-Gomes,Willem Bouten,François Sarrazin,Olivier Duriez,Simon Benhamou,Dustin Rubenstein

doi:10.1371/journal.pone.0053077

Abstract

Feeding stations are commonly used to sustain conservation programs of scavengers but their impact on behaviour is still debated. They increase the temporal and spatial predictability of food resources while scavengers have supposedly evolved to search for unpredictable resources. In the Grands Causses (France), a reintroduced population of Griffon vultures Gyps fulvus can find carcasses at three types of sites: 1. “light feeding stations”, where farmers can drop carcasses at their farm (spatially predictable), 2. “heavy feeding stations”, where carcasses from nearby farms are concentrated (spatially and temporally predictable) and 3. open grasslands, where resources are randomly distributed (unpredictable). The impact of feeding stations on vulture’s foraging behaviour was investigated using 28 GPS-tracked vultures. The average home range size was maximal in spring (1272±752 km2) and minimal in winter (473±237 km2) and was highly variable among individuals. Analyses of home range characteristics and feeding habitat selection via compositional analysis showed that feeding stations were always preferred compared to the rest of the habitat where vultures can find unpredictable resources. Feeding stations were particularly used when resources were scarce (summer) or when flight conditions were poor (winter), limiting long-ranging movements. However, when flight conditions were optimal, home ranges also encompassed large areas of grassland where vultures could find unpredictable resources, suggesting that vultures did not lose their natural ability to forage on unpredictable resources, even when feeding stations were available. However during seasons when food abundance and flight conditions were not limited, vultures seemed to favour light over heavy feeding stations, probably because of the reduced intraspecific competition and a pattern closer to the natural dispersion of resources in the landscape. Light feeding stations are interesting tools for managing food resources, but don’t prevent vultures to feed at other places with possibly high risk of intoxication (poison).

Highlights

Human intervention on wildlife through conservation programs raises many questions about its impacts on populations and individual behaviour
We considered the following four basic variables: 1. home range area; 2. core areas, 3. number of feeding stations (HFS and Light Feeding Stations’’ (LFS) pooled) encompassed in the home range, and 4. mean distance covered per day
A general gross home range estimated with Minimum Convex Polygon (MCP) method pooling all individual covered .10000 km2 and encompassed all the feeding sites

Summary

Introduction

Human intervention on wildlife through conservation programs raises many questions about its impacts on populations and individual behaviour. In India, feeding stations are supposed to provide a safe food source after millions of vultures were decimated by the contamination of carrion by a veterinary drug in the 1990s [8,9]. This conservation measure is used to provide carcasses in areas with insufficient food [10], to increase survival [11], to facilitate the recolonization of abandoned breeding sites [7] and to support reintroduction programs [12,13]

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Conclusion