Factors affecting offspring survival and development in a cooperative bird: social, maternal and environmental effects

Authors


and present address: Percy Fitzpatrick Institute, DST/NRF Centre of Excellence, University of Cape Town, Rondebosch 7701, South Africa. Tel.: +27 216503634/3291. Fax: +27 216503295. E-mail: aridley@botzoo.uct.ac.za

Summary

  • 1In many noncooperative vertebrates, maternal effects commonly influence offspring survival and development. In cooperative vertebrates, where multiple adults help to raise young from a single brood, social effects may reduce or replace maternal effects on offspring.
  • 2Factors affecting offspring survival and development at different stages (fledging, nutritional independence and adulthood) were tested in the cooperatively breeding Arabian babbler to determine the relative importance of social, maternal and environmental factors at each stage. An influence of maternal effects was found during the nestling stage only.
  • 3Social factors affected the survival and development of young at all stages. The amount of food received from helpers influenced post-fledging weight gain, development of foraging skills, and survival to reproductive age. Environmental effects were also important, with groups occupying high-quality territories more likely to produce young that survived to maturity.
  • 4The strong influence of helper contributions on the survival and development of young at all stages from hatching to maturity suggests social factors may have important long-term effects on offspring fitness in cooperative societies. Traditional measures of offspring survival in cooperative birds, which commonly measure survival to fledging age only, may underestimate the significant benefit of helper contributions on the survival and development of young.

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