Vultures acquire information on carcass location from scavenging eagles

Adam Kane,Darcy L Ogada,Ara Monadjem,Andrew L Jackson,Luke Mcnally

doi:10.1098/rspb.2014.1072

Abstract

Vultures are recognized as the scroungers of the natural world, owing to their ecological role as obligate scavengers. While it is well known that vultures use intraspecific social information as they forage, the possibility of inter-guild social information transfer and the resulting multi-species social dilemmas has not been explored. Here, we use data on arrival times at carcasses to show that such social information transfer occurs, with raptors acting as producers of information and vultures acting as scroungers of information. We develop a game-theoretic model to show that competitive asymmetry, whereby vultures dominate raptors at carcasses, predicts this evolutionary outcome. We support this theoretical prediction using empirical data from competitive interactions at carcasses. Finally, we use an individual-based model to show that these producer–scrounger dynamics lead to vultures being vulnerable to declines in raptor populations. Our results show that social information transfer can lead to important non-trophic interactions among species and highlight important potential links among social evolution, community ecology and conservation biology. With vulture populations suffering global declines, our study underscores the importance of ecosystem-based management for these endangered keystone species.

Highlights

Animals base their decisions on both personal and public information [1,2,3,4]
The results of our model demonstrate the potential importance of competitive asymmetry in the evolutionary outcome of inter-guild producer–scrounger dynamics
Our results suggest that there is a producer –scrounger game occurring between Gyps vultures and scavenging raptors, with the competitive dominance of vultures favouring a scrounging strategy on their part

Summary

Introduction

Animals base their decisions on both personal and public information [1,2,3,4]. This is applicable to every facet of an animal’s life, be it feeding, movement, mating, etc., with high fidelity information allowing an individual to make decisions conducive to its survival [1,5,6]. Consider the social Gyps vultures, a group that is known to forage collectively for carrion. Once one vulture discovers and descends to a carcass, the information is conveyed to others in the area; this activity can create a local enhancement effect [14] Such social behaviour renders vultures’ foraging efficiency susceptible to population declines; with every individual lost, the network is less effective at detecting carrion [14]. The African white-backed vulture has been noted in using many other scavengers as a means of local enhancement while foraging [9] These heterospecific interactions and their potential for information transfer have not been explored in any detail [17]. We conclude by outlining the consequences of this system’s properties for vulture conservation

Test for producer–scrounger dynamics

Producer–scrounger model

Test of competitive ability

Effects of raptor density on vulture foraging efficiency

Findings

Discussion