title: Functional traits determine heterospecific use of risk-related social information in forest birds of tropical South-East Asia.
abstract: In birds and mammals, mobbing calls constitute an important form of social information that can attract numerous sympatric species to localized mobbing aggregations. While such a response is thought to reduce the future predation risk for responding species, there is surprisingly little empirical evidence to support this hypothesis. One way to test the link between predation risk reduction and mobbing attraction involves testing the relationship between species' attraction to mobbing calls and the functional traits that define their vulnerability to predation risk. Two important traits known to influence prey vulnerability include relative prey-to-predator body size ratio and the overlap in space use between predator and prey; in combination, these measures strongly influence prey accessibility, and therefore their vulnerability, to predators. Here, we combine community surveys with behavioral experiments of a diverse bird assemblage in the lowland rainforest of Sumatra to test whether the functional traits of body mass (representing body size) and foraging height (representing space use) can predict species' attraction to heterospecific mobbing calls. At four forest sites along a gradient of forest degradation, we characterized the resident bird communities using point count and mist-netting surveys, and determined the species groups attracted to standardized playbacks of mobbing calls produced by five resident bird species of roughly similar body size and foraging height. We found that (1) a large, diverse subcommunity of bird species was attracted to the mobbing calls and (2) responding species (especially the most vigorous respondents) tended to be (a) small (b) mid-storey foragers (c) with similar trait values as the species producing the mobbing calls. Our findings from the relatively lesser known bird assemblages of tropical Asia add to the growing evidence for the ubiquity of heterospecific information networks in animal communities, and provide empirical support for the long-standing hypothesis that predation risk reduction is a major benefit of mobbing information networks.
authors.affiliation: State Key Laboratory of BioControl College of Ecology and Evolution/School of Life Sciences Sun Yat-sen University Guangzhou Guangdong China; Program in Science, Technology, and Environmental Policy Woodrow Wilson School of Public and International Affairs Princeton University Princeton NJ USA.
authors.forename: Fangyuan
authors.initials: F
authors.lastname: Hua
authors.affiliation: Fenner School of Environment and Society the Australian National University Canberra ACT Australia.
authors.forename: Ding Li
authors.initials: DL
authors.lastname: Yong
authors.affiliation: Biology Department Faculty of Mathematics and Natural Science Andalas University Padang West Sumatra Indonesia.
authors.forename: Muhammad Nazri
authors.initials: MN
authors.lastname: Janra
authors.affiliation: Biology Department Faculty of Mathematics and Natural Science Andalas University Padang West Sumatra Indonesia.
authors.forename: Liza M
authors.initials: LM
authors.lastname: Fitri
authors.affiliation: Indonesian Institute of Technology (LIPI) Cibinong West Java Indonesia.
authors.forename: Dewi
authors.initials: D
authors.lastname: Prawiradilaga
authors.affiliation: Department of Wildlife Ecology and Conservation College of Agriculture and Life Sciences University of Florida Gainesville FL USA.
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Sieving
keywords: functional traits; mobbing; predation risk; social information; tropical rainforest