Flexural stiffness of feather shafts: geometry rules over material properties
Abstract
Flight feathers of birds interact with the flow field during flight. They bend and twist under aerodynamic loads. Two parameters are mainly responsible for flexibility in feathers: the elastic modulus (Young's modulus, E) of the material (keratin) and the geometry of the rachises, more precisely the second moment of area (I). Two independent methods were employed to determine Young's modulus of feather rachis keratin. Moreover, the second moment of area and the bending stiffness of feather shafts from fifth primaries of barn owls (Tyto alba) and pigeons (Columba livia) were calculated. These species of birds are of comparable body mass but differ in wing size and flight style. Whether their feather material (keratin) underwent an adaptation in stiffness was previously unknown. This study shows that no significant variation in Young's modulus between the two species exists. However, differences in Young's modulus between proximal and distal feather regions were found in both species. Cross-sections of pigeon rachises were particularly well developed and rich in structural elements, exemplified by dorsal ridges and a well-pronounced transversal septum. In contrast, cross-sections of barn owl rachises were less profiled but had a higher second moment of area. Consequently, the calculated bending stiffness (EI) was higher in barn owls as well. The results show that flexural stiffness is predominantly influenced by the geometry of the feathers rather than by local material properties.
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The position dependence of bending stiffness in the lateral direction for the eyespot feathers is similar to that found for flight and tail feathers in other bird species.
“The position dependence of bending stiffness in the lateral direction for the eyespot feathers (as shown by I in Fig 8D) is similar to that found for flight and tail feathers in other bird species [38, 43].”
From Biomechanics of the Peacock’s Display: How Feather Structure and Resonance Influence Multimodal Signaling (2016) · cites this paper as [38]
The magnitude of the second moment of area, I, for short eyespot feathers is only 28% of that of owl and pigeon flight feathers of similar length.
“the magnitude of the second moment of area, I, for short eyespot feathers is only 28% of that of owl and pigeon flight feathers of similar length [38].”
From Biomechanics of the Peacock’s Display: How Feather Structure and Resonance Influence Multimodal Signaling (2016) · cites this paper as [38]
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- Authors
- Bachmann, T., Emmerlich, J., Baumgartner, W., Schneider, J. M., & Wagner, H.
- Affiliations
- Technische Universität Darmstadt (DE)
- RWTH Aachen University (DE)
- Institute for Biology II, RWTH Aachen University, Mies-van-der-Rohe-Strasse 15, 52074 Aachen, Germany
- Corresponding author
- Bachmann, Thomas
- Venue
- Journal of Experimental Biology
- Publisher
- The Company of Biologists
- Published
- 2012-02-01
- Volume
- 215
- Issue
- 3
- Pages
- 405-415
- ISSN
- 0022-0949 (ISSN-L)
- 1477-9145
- OpenAlex
- W1994497159
- Cited by
- 107
- References
- 37
- Citations by year
- 2026: 7 · 2025: 12 · 2024: 8 · 2023: 7 · 2022: 17 · 2021: 4 · 2020: 11 · 2019: 9 · 2018: 3 · 2017: 7 · 2016: 7 · 2015: 7 · 2014: 4 · 2013: 2 · 2012: 2
- FWCI
- 8.06
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Journal of Experimental Biology (publishedVersion)
- PubMed (publishedVersion)
- RWTH Publications (RWTH Aachen) (submittedVersion)
- Topics
- Physical Sciences › Engineering › Aerospace Engineering › Biomimetic flight and propulsion mechanisms
- Physical Sciences › Engineering › Aerospace Engineering › Aeroelasticity and Vibration Control
- Health Sciences › Medicine › Urology › Comparative Animal Anatomy Studies
- Keywords
- flight feathers, bending stiffness, Young's modulus, keratin, second moment of area, barn owl, pigeons, bird flight, aerodynamic forces, cross-sectional geometry, material properties
- MeSH terms
- Animals, Biomechanical Phenomena, Feathers, Flight, Animal, Keratins, Columbidae, Wings, Animal, Pliability, Strigiformes, Elastic Modulus
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