Abstract
Bird wings exhibit a broad degree of functional and shape variation, though the exact nature of the form-function relationship is uncertain. Recent analysis suggests that functional variability is explained by linear non-shape-based traits and that shape variation is largely explained by phylogeny. We assay the relationship between wing planform shape and functional performance using a theoretical morphospace approach that eschews assumptions of the functional optimality of empirical morphologies. Hypothesised empirical properties are considered post hoc relative to their positions in performance surfaces. We produce a theoretical morphospace of wing planform shape and deduce the functional performance and optimality of 1139 extant taxa. Functional tests cover metrics and combinations with a hypothesised link to 7 flight niches. Metrics pertaining to agile flight strongly constrain shape, with hovering, diving and hawking birds developing optimal planforms. Marine soarers are suboptimal for metrics linked with low cost of transport and manoeuvrable flight. Many taxa, principally passerines, are suboptimal for all studied metrics and combinations demonstrating uneven constraint on flight performace across birds. Phylomorphospace analysis suggests planform shape is only weakly influenced by phylogeny and functional optimality correlates closely with flight styles. This suggests wing shape remains a determining factor in how birds fly.
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Data availability
All data used in and generated by this study have been deposited and are accessible on Figshare at https://doi.org/10.6084/m9.figshare.31353850. Additionally, the previously unpublished Rayner dataset of birds has been made available as Supplementary Data 5. All data uploaded are freely available without restrictions. The original location and institution of all wing data collected for this study are available in the ‘Taxa Set’ file, located in Supplementary Data 1.
Code availability
The base code used in this study both for analysis and for the generation of all figure elements is available on Github, accessible at Deakin, W. J., Rayfield, E. J., & Donoghue, P. C. theofun (Version 0.0.1) [Computer software]. https://github.com/Bristol-Palaeobiology/theofun). All executable files and modifications of the base code have been made available in Supplementary Code 1, accessible on Figshare at https://doi.org/10.6084/m9.figshare.31353850. All code files uploaded are freely available without restrictions.
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Acknowledgements
The authors would like to thank Jeremy Rayner for providing access to his original bird data and taxa set; Will Deakin for guidance and support in the application of the theofun pipeline; Mark Adams at the Natural History Museum, Tring, and Chris Wood and Kevin Epperly at the Burke Museum of Natural History and Culture for allowing access to their collections and facilitating data collection. We also thank artists Andy Wilson, Alexandre Vong, Ferran Sayol, and Sharon Wegner-Larsen for making available their bird silhouettes on Phylopic and the editor and reviewers of this article for their insightful feedback. The authors would also like to acknowledge the following funding sources: the John Templeton Foundation (JTF62574 E.J.R. and P.C.J.D.), the Leverhulme Trust (RF-2022-167 P.C.J.D.), the Biotechnology and Biological Sciences Research Council (BB/W00867X/1 E.J.R.). The opinions within this article are those of the authors and do not necessarily reflect those of the John Templeton Foundation.
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Conceptualisation: B.W., E.J.R., P.C.J.D. Methodology: B.W., Y.L., E.J.R., P.C.J.D. Software: Y.L., E.J.R., P.C.J.D. Investigation: B.W. Visualisation: B.W. Supervision: E.J.R., P.C.J.D. Writing – original draft: B.W. Writing – review and editing: B.W., Y.L., E.J.R., P.C.J.D.
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Walters, B., Liu, Y., Rayfield, E.J. et al. Theoretical morphospace reveals mixed optimisation of the avian wing planform for flight style. Nat Commun (2026). https://doi.org/10.1038/s41467-026-70692-w
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DOI: https://doi.org/10.1038/s41467-026-70692-w
