title: Variation in helper effort among cooperatively breeding bird species is consistent with Hamilton's Rule.
abstract: Investment by helpers in cooperative breeding systems is extremely variable among species, but this variation is currently unexplained. Inclusive fitness theory predicts that, all else being equal, cooperative investment should correlate positively with the relatedness of helpers to the recipients of their care. We test this prediction in a comparative analysis of helper investment in 36 cooperatively breeding bird species. We show that species-specific helper contributions to cooperative brood care increase as the mean relatedness between helpers and recipients increases. Helper contributions are also related to the sex ratio of helpers, but neither group size nor the proportion of nests with helpers influence helper effort. Our findings support the hypothesis that variation in helping behaviour among cooperatively breeding birds is consistent with Hamilton's rule, indicating a key role for kin selection in the evolution of cooperative investment in social birds.
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.
authors.forename: Jonathan P
authors.identifier: 0000-0001-8728-2810
authors.initials: JP
authors.lastname: Green
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.
authors.forename: Robert P
authors.identifier: 0000-0002-8338-864X
authors.initials: RP
authors.lastname: Freckleton
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Hatchwell
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D005075:Biological Evolution; D001717:Birds / Q000502:physiology*; D001947:Breeding; D003299:Cooperative Behavior; D017753:Ecosystem; D005260:Female; D006379:Helping Behavior; D008297:Male; D008954:Models, Biological; D010802:Phylogeny; D012744:Sex Ratio; D012919:Social Behavior; D013045:Species Specificity