Abstract
Phenotypic trait data play a central role in ecology and evolutionary research. The quality of trait data, and the findings of subsequent analyses, depend on the quality of measurement. However, most studies overlook measurement accuracy in their study designs. We investigated the repeatability of five frequently used linear measurements of avian traits: wing length, tarsus length, bill length, bill depth and bill width and the validity of proxies for three traits: bill surface area, structural body size and tarsus size, using species from the infra-order Meliphagides (honeyeaters, fairy wrens and their allies). Repeatability varied between traits and across species for a given trait: traits larger than 13 mm showed high repeatability compared with smaller traits. By incorporating microCT technology, we showed that the formula for the surface area of a cone, a widely used proxy of bill surface area, accurately describes bill surface area within species. Surface measurement of tarsus and wing lengths were valid proxies for underlying osteology. We recommend preliminary estimation of repeatability should be undertaken for individual traits prior to data collection, in order to design suitable protocols that improve data quality, while optimizing costs involved, particularly for traits < 13 mm.
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(“Illustrations by Peter Marsack, reproduced from Menkhorst et al. (2017), The Australian Bird Guide, with permission from CSIRO Publishing”)
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Acknowledgements
We thank Jesse Smith and Roellen Little for undertaking all wing measurements, and the staff at The Australian National Wildlife Collection, Australian Museum, Museum Victoria, Queensland Museum, Queen Victoria Museum and Art Gallery, South Australian Museum, Western Australian Museum, Tasmanian Museum and Art gallery for providing access to specimens. We also thank Emma Sherratt for general advice on 3D imaging and analysis, Terry Neeman at ANU, for advice on statistical analyses, and Cathy Gillespie at the John Curtin School of Medical Research, ANU, for technical assistance in 3D imaging and Peter Marsack for allowing us to use his bird illustrations. We are also grateful to an anonymous reviewer, Lynda Sharpe and Heather McGinness for helpful comments on the draft manuscript.
Funding
This work was partly funded by The Commonwealth Scientific and Industrial Research Organisation (PHD17-27) and the Recent Ecological Change in Australia project through the Department of Agriculture, Water and Environment (DAWE). KS was supported by ANU HDR Fee Merit Scholarship, University Research Scholarship and CSIRO research plus top-up scholarship (PHD17-27). MVG is supported by the University of Calgary's Banting Research Allowance and an ACHRI Postdoctoral Fellowship.
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KS and JG conceived the idea; KS, JG and MVG developed the methods; KS, TB and MRES designed the analyses; KS collected and analysed the data and wrote the manuscript; all authors read the manuscript and provided feedback.
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Subasinghe, K., Symonds, M.R.E., Vidal-García, M. et al. Repeatability and Validity of Phenotypic Trait Measurements in Birds. Evol Biol 48, 100–114 (2021). https://doi.org/10.1007/s11692-020-09527-5
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DOI: https://doi.org/10.1007/s11692-020-09527-5