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Philornis downsi parasitism is the primary cause of nestling mortality in the critically endangered Darwin’s medium tree finch (Camarhynchus pauper)

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Abstract

Darwin’s medium tree finch (Camarhynchus pauper) meets the 2009 International Union for Conservation of Nature Red List criteria for a critically endangered species because it has “a very small range on a single island” and is “declining rapidly owing to the effects of the parasite Philornis downsi”, habitat degradation, and introduced predators. The medium tree finch is only found in patches of remnant highland forest on Floreana Island, where it co-exists with breeding populations of small and large tree finches (C. parvulus and C. psittacula). Here, we examine the intensity of P. downsi in nests of small, medium, and large tree finches on Floreana. We expected that parasite intensity would increase with finch body size, and with greater rainfall, and would also correlate with increased nestling mortality. We found a trend in the expected direction for parasite intensity and rainfall. Combined meta-analytically with data from a previous study, the overall trend for the two studies was significant. We also found a significant linear trend in parasite intensity with finch body size. In addition, the medium tree finch exhibited a somewhat higher parasite intensity than would be expected based on body mass alone. Of 63 active medium tree finch nests, 17 nests had nestlings: all of which were infested with P. downsi. Only 25% of medium tree finch nestlings fledged, 28% were depredated, 41% died due to P. downsi parasitism, and 6% died for other reasons.

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Acknowledgments

This paper is contribution number 2003 of the Charles Darwin Foundation for the Galápagos Islands. We are grateful to the Charles Darwin Research Station and Galápagos National Park Service for the opportunity to work on the Galápagos, and for logistical support. This work was generously supported by Flinders University (Research Establishment Grant to SK), Conservation International, the Winifred Violet Scott Trust, and the American Bird Conservancy with awards to SK and also the Royal Zoological Society of South Australia, and the Australian Federation of University Women (SA) with awards to JO’C. TAME airlines provided reduced airfares. We thank Rebekah Christensen and Santos Humberto for field assistance, and Rachael Dudaniec for field assistance and comments on the manuscript. We extend special thanks to the community of Floreana Island, and the local National Parks team for their invaluable assistance and support.

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Authors and Affiliations

  1. School of Biological Sciences, Flinders University, GPO Box 2100, Adelaide, SA, 5001, Australia

    Jody A. O’Connor, Jeremy Robertson & Sonia Kleindorfer

  2. Institute of Personality and Social Research, University of California, 4125 Tolman Hall, Berkeley, CA, 94720, USA

    Frank J. Sulloway

Authors
  1. Jody A. O’Connor
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  2. Frank J. Sulloway
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  3. Jeremy Robertson
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  4. Sonia Kleindorfer
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Correspondence to Sonia Kleindorfer.

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O’Connor, J.A., Sulloway, F.J., Robertson, J. et al. Philornis downsi parasitism is the primary cause of nestling mortality in the critically endangered Darwin’s medium tree finch (Camarhynchus pauper). Biodivers Conserv 19, 853–866 (2010). https://doi.org/10.1007/s10531-009-9740-1

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  • DOI: https://doi.org/10.1007/s10531-009-9740-1

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