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Behavioral Ecology and Sociobiology

, Volume 63, Issue 1, pp 103–112 | Cite as

Helpers in colonial cooperatively breeding sociable weavers Philetairus socius contribute to buffer the effects of adverse breeding conditions

  • Rita CovasEmail author
  • Morné A. du Plessis
  • Claire Doutrelant
Original Paper

Abstract

Some studies on the effects of helpers in cooperatively breeding vertebrates show a positive effect of helper presence on reproductive output whereas others find no effect. One possibility for this discrepancy is that helpers may have a positive effect when breeding conditions are adverse, while their effect might go unnoticed under good conditions. We investigate this hypothesis on sociable weavers Philetairus socius, a colonial cooperatively breeding passerine that inhabits a semi-arid region where breeding conditions vary markedly. We used multivariate mixed models to analyse the effect of helpers on reproduction under contrasting environmental and social conditions while controlling for parental and colony identity. We found that reproductive success in sociable weavers was primarily influenced by nest predation and rainfall. In addition, colony size was negatively associated with hatching and fledging success and number of young fledged per season. Helpers had a less prominent but significant influence on feeding rates and reproductive outcome. In agreement with expectations, the presence of helpers counteracted some of the negative effects of breeding in periods of low rainfall or in large colonies and was also associated with an increased number of young fledged per season. Our results illustrate that the effect of helpers might be detectable mostly under unfavourable conditions, but can contribute to improve reproductive performance in those situations.

Keywords

Colony size Cooperative breeding Environmental stochasticity Group size Reproductive success 

Notes

Acknowledgments

This work would have not been possible without the help of our volunteer field assistants: I. Barr, A. Charmantier, G. Curti, L. Lesobre, D. Logan, M. Melo, S. Molony, M. Pieraard, T. Pontynen, J. Scholliers, B. Verbraak, M. Verzjiden and R. Visagie. We thank M. Griesser, C. Spottiswoode, S.A. West and anonymous reviewers for comments that helped improve earlier versions of the manuscript. De Beers Consolidated Mining Ltd. kindly provided access to the study site. Logistic support and help with various issues in the field was provided by M. D. Anderson and the Department of Tourism, Environment & Conservation (DTEC) of South Africa. The work was conduct under permission from the DTEC and Ethics Council from the University of Cape Town and from the Northern Cape Nature Conservation office. The study was funded by grants from the South African National Research Foundation to MduP and CD. RC was supported by Program Praxis XXI-BD11497/97 (FCT, Portugal). Additional funding during the writing-up stages was obtained from Program Alliance (France–UK).

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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • Rita Covas
    • 1
    • 2
    • 3
    Email author
  • Morné A. du Plessis
    • 1
  • Claire Doutrelant
    • 1
    • 3
  1. 1.Percy FitzPatrick InstituteUniversity of Cape TownRondeboschSouth Africa
  2. 2.CIBIOUniversity of PortoVairãoPortugal
  3. 3.CEFE–CNRSMontpellier cedex 5France

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