Behavioral Ecology Advance Access originally published online on February 16, 2009
Behavioral Ecology 2009 20(3):469-477; doi:10.1093/beheco/arp019
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The effect of social facilitation on vigilance in the eastern gray kangaroo, Macropus giganteus
a Laboratoire Paysages & Biodiversité, Université d'Angers, Campus Belle Beille, 2 bd Lavoisier, 49045 Angers Cedex, France b School of Integrative Biology, University of Queensland, St. Lucia, Brisbane, QLD 4072, Australia c Institut National de Recherche Agronomique Toulouse, Unité Mixte de Recherche 1201 Dynafor, Castanet-Tolosan, France d Faculty of Biological and Chemical Sciences, University of Queensland, St. Lucia, Brisbane, QLD 4072, Australia e Laboratoire Ecobio, Unité Mixte de Recherche Centre National de Recherche Scientifique 6553, Université de Rennes 1, Campus de Beaulieu, Rennes, France f Ecosystem Management, University of New England, Armidale, NSW 2351, Australia
Address correspondence to O. Pays. E-mail: olivier.pays{at}univ-angers.fr.
| Abstract |
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The relevance of vigilance activity to predator detection has been demonstrated in numerous studies. However, few studies have investigated the effect of one group member being vigilant on the probability of others being vigilant in group-forming prey species. Thus, we studied vigilance activity of eastern gray kangaroos Macropus giganteus that still experience occasional predation. We video recorded the behavior of all group members simultaneously and investigated the probability of a focal group member being vigilant (or nonvigilant) in relation to other individuals' vigilant and nonvigilant behaviors. Our results show that the decision of an individual to exhibit a vigilant posture depended on what it and other group members had been doing (scanning or foraging) at the preceding second and on group size. The probability of an individual being vigilant was positively affected by the proportion of companions that were vigilant at the previous second, confirming the existence in this species of a tendency for synchronization of individual vigilance. Group size affected individuals' vigilance in 3 ways. First, individuals were more likely to be vigilant if the proportion of their group mates that was vigilant was high, and this was strengthened with increasing group size. Second, the effect of the individual's own vigilance state (vigilant or not) at the previous second also increased with group size. Third, the probability of an individual being vigilant decreased with group size. These findings increase our understanding of the much-studied relationship between vigilance and group size.
Key words: allelomimesis, group size, kangaroos, neighbor effect, probability of being vigilant, social facilitation, vigilance.
Received 3 October 2008; revised 5 December 2008; accepted 5 December 2008.