Variable fledging age according to group size

Trade-offs in a cooperatively breeding bird

N. J. Raihani*, A. R. Ridley

*Corresponding author for this work

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

Group living can provide individuals with several benefits, including cooperative vigilance and lower predation rates. Individuals in larger groups may be less vulnerable to predation due to dilution effects, efficient detection or greater ability to repel predators. Individuals in smaller groups may consequently employ alternative behavioural tactics to compensate for their greater vulnerability to predators. Here, we describe how pied babbler (Turdoides bicolor) fledging age varies with group size and the associated risk of nestling predation. Nestling predation is highest in smaller groups, but there is no effect of group size on fledgling predation. Consequently, small groups fledge young earlier, thereby reducing the risk of predation. However, there is a cost to this behaviour as younger fledglings are less mobile than older fledglings: they move shorter distances and are less likely to successfully reach the communal roost tree. The optimal age to fledge young appears to depend on the trade-off between reduced nestling predation and increased fledgling mobility. We suggest that such trade-offs may be common in species where group size critically affects individual survival and reproductive success.

Original languageEnglish
Pages (from-to)624-627
Number of pages4
JournalBiology Letters
Volume3
Issue number6
DOIs
Publication statusPublished - 22 Dec 2007

Keywords

  • Fledging age
  • Group size
  • Nestling development
  • Pied babbler
  • Predation
  • Trade-off

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