title: The anti-predator role of within-nest emergence synchrony in sea turtle hatchlings.
abstract: Group formation is a common behaviour among prey species. In egg-laying animals, despite the various factors that promote intra-clutch variation leading to asynchronous hatching and emergence from nests, synchronous hatching and emergence occurs in many taxa. This synchrony may be adaptive by reducing predation risk, but few data are available in any natural system, even for iconic examples of the anti-predator function of group formation. Here, we show for the first time that increased group size (number of hatchlings emerging together from a nest) reduces green turtle (Chelonia mydas) hatchling predation. This effect was only observed earlier in the night when predation pressure was greatest, indicated by the greatest predator abundance and a small proportion of predators preoccupied with consuming captured prey. Further analysis revealed that the effect of time of day was due to the number of hatchlings already killed in an evening; this, along with the apparent lack of other anti-predatory mechanisms for grouping, suggests that synchronous emergence from a nest appears to swamp predators, resulting in an attack abatement effect. Using a system with relatively pristine conditions for turtle hatchlings and their predators provides a more realistic environmental context within which intra-nest synchronous emergence has evolved.
authors.affiliation: Instituto de Ciências Biológicas e da Saúde, Universidade Federal de Alagoas, Maceió, Alagoas, Brazil robsongsantos@gmail.com.
authors.forename: Robson G
authors.identifier: 0000-0001-5240-6799
authors.initials: RG
authors.lastname: Santos
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California Santa Cruz, Santa Cruz, CA, USA California Academy of Sciences, San Francisco, CA, USA.
authors.forename: Hudson Tercio
authors.initials: HT
authors.lastname: Pinheiro
authors.affiliation: Departamento de Oceanografia e Ecologia, Universidade Federal do Espírito Santo, Vitória, Espirito Santo, Brazil.
authors.forename: Agnaldo Silva
authors.initials: AS
authors.lastname: Martins
authors.affiliation: Departamento de Engenharia e Meio Ambiente, CCAE, Universidade Federal da Paraíba, Rio Tinto, Paraíba, Brazil.
authors.forename: Pablo
authors.initials: P
authors.lastname: Riul
authors.affiliation: Fundação Pró-Tamar, Escritório Regional de Vitória, Vitória, Espirito Santo, Brazil.
authors.forename: Soraya Christina
authors.initials: SC
authors.lastname: Bruno
authors.affiliation: Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA, USA.
authors.forename: Fredric J
authors.initials: FJ
authors.lastname: Janzen
authors.affiliation: School of Biological Sciences, University of Bristol, Bristol BS8 1TQ, UK.
authors.forename: Christos C
authors.identifier: 0000-0002-9739-889X
authors.initials: CC
authors.lastname: Ioannou
mesh_terms: D000818:Animals; D001683:Biological Clocks; D011235:Predatory Behavior; D014426:Turtles / Q000502:physiology*
keywords: anti-predator behaviour; attack abatement; dilution effect; predation risk; sea turtles; synchronous hatching