Beak of the pinch: anti-parasite traits are similar among Darwin’s finch species
Darwin’s finches are an iconic example of adaptive radiation. The size and shape of the beaks of different finch species are diversified for feeding on different size seeds and other food resources. However, beaks also serve other functions, such as preening for the control of ectoparasites. In diverse groups of birds, the effectiveness of preening is governed by the length of the overhanging tip of the upper mandible of the beak. This overhang functions as a template against which the tip of the lower mandible generates a pinching force sufficient to damage or kill ectoparasites. Here we compare feeding versus preening components of the beak morphology of small, medium, and large ground finches that share a single parasite community. Despite adaptive divergence in beak morphology related to feeding, the three species have nearly identical relative mandibular overhang lengths. Moreover, birds with intermediate length overhangs have the lowest feather mite loads. These results suggest that Darwin’s finches maintain an optimal beak morphology to effectively control their ectoparasites.
KeywordsPreening Feather mites Geospiza Principal component analysis Overhang
We thank S. Bush, D. Feener, E. Diblasi, J. Ruff, S. McNew, T. White, and the two anonymous reviewers for comments that greatly strengthened the manuscript. We also thank J. Podos and K. Gotanda for use of their photographs. All procedures were approved by University of Utah Institutional Animal Care and Use Committee (protocol #07-08004) and with permission from the Galapagos National Park (PC-04-10: #0054411). This work was funded by the National Science Foundation DEB-0816877 to DHC and Sigma Xi Grants-in-aid of Research to JAHK.
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Conflict of interest
The authors declare that they have no conflict of interest.
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