title: Parental effort and reproductive skew in coalitions of brood rearing female common eiders.
abstract: Members of breeding groups face conflicts over parental effort when balancing antipredatory vigilance and feeding. Empirical evidence has shown disparate responses to manipulations of parental effort. We develop a model in which we determine the evolutionarily stable effort of partners given their body conditions, allowing the benefits of shared care to be unevenly divided, and we test this model's predictions with data on common eiders (Somateria mollissima). Eiders show uniparental female care; females may share brood rearing, or they may tend alone, and their body condition at hatching of the young shows large environmentally induced variation. The model predicts that parental effort (vigilance) in a coalition is lower than when tending alone, controlling for parental condition; this prediction is supported by the data. The parental effort in a coalition should be positively correlated with body condition, and this prediction is also supported. Finally, parental effort should increase when partner condition decreases and vice versa; this prediction is partially supported. The Nash bargaining game may provide promising avenues by which to determine the precise settlement of reproductive skew and effort between coalition partners in the future.
authors.affiliation: Bird Ecology Unit, Department of Biological and Environmental Sciences, University of Helsinki, P.O. Box 65 (Biocenter 3, Viikinkaari 1), FI-00014 Helsinki, Finland. markus.ost@helsinki.fi
authors.forename: Markus
authors.initials: M
authors.lastname: Ost
authors.forename: Colin W
authors.initials: CW
authors.lastname: Clark
authors.forename: Mikael
authors.initials: M
authors.lastname: Kilpi
authors.forename: Ron
authors.initials: R
authors.lastname: Ydenberg
mesh_terms: D000818:Animals; D004372:Ducks / Q000502:physiology*; D005260:Female; D008954:Models, Biological; D009425:Nesting Behavior / Q000502:physiology*; D012098:Reproduction