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Journal of Ornithology

, Volume 150, Issue 2, pp 383–391 | Cite as

Jack-of-all-trades or master of one? Variation in foraging specialisation across years in Darwin’s Tree Finches (Camarhynchus spp.)

  • Rebekah Christensen
  • Sonia KleindorferEmail author
Original Article

Abstract

Theory predicts that species should have wider foraging niches during conditions of resource scarcity. However, empirical evidence to date has shown mixed patterns, including studies of Darwin’s finches that have found narrower foraging niches during conditions of resource scarcity. Here, we compare foraging behaviour in three species of Darwin’s Tree Finches (Camarhynchus spp.) in a dry versus wet year on Floreana Island to examine the change in foraging breadth under conditions of resource scarcity. We provide descriptive data on diet, foraging substrate, technique, height, and foraging time across the Small Tree Finch (C. parvulus), Medium Tree Finch (C. pauper), and Large Tree Finch (C. psittacula). During dry versus wet years, we made the following predictions: (1) lower intraspecific niche breadth (that is, a higher level of specialisation), (2) lower interspecific overlap in all foraging parameters, and (3) longer foraging times due to relative resource scarcity. Our findings showed that the Small and Medium Tree Finches were generalist foragers, while the Large Tree Finch was a specialist. Resource specialisation varied across years of differing rainfall: both generalist species were less specialised (higher Shannon diversity index) during the dry year, while the specialist species was more specialised (lower Shannon diversity index).

Keywords

Annual variation Extinction risk Foraging Rainfall Specialisation 

Notes

Acknowledgments

We are grateful to the Charles Darwin Research Station and Galapagos National Park Service for the opportunity to work on the Galapagos Archipelago and for invaluable logistical support in the field. This study was generously funded by Flinders University (Research Establishment Grant to SK, Overseas Field Trip Grant to R.C.), Conservation International and the American Bird Conservancy with awards to S.K., and the Australian Federation of University Women SA with a Barbara Crase Bursary to R.C.; TAME airlines provided reduced airfares. Many thanks to Jody O’Connor and Jeremy Robertson for their invaluable assistance in the field, and to Dolph Schluter for stimulating discussion about this manuscript. We are especially grateful to the Cruz and Wittmer families, and the community of Puerto Velasco Ibarra, Floreana Island, for their hospitality, transport assistance, and support. All work followed the Guidelines for the Use of Animals in Research (Flinders University, Charles Darwin Research Station, Galapagos National Parks Service), met the legal requirements of Ecuador, and was approved by the Animal Welfare Committee of Flinders University (Permit E129).

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Copyright information

© Dt. Ornithologen-Gesellschaft e.V. 2008

Authors and Affiliations

  1. 1.School of Biological SciencesFlinders UniversityAdelaideAustralia

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