The Young's modulus of feather keratin

Area of Science:

• Biomechanics
• Materials Science
• Avian Biology

Background:

• The flexural stiffness of a bird's primary feather rachis varies.
• The contribution of feather keratin's material properties to this variation is unknown.

Purpose of the Study:

• To assess the role of longitudinal Young's modulus of feather keratin in rachis flexural stiffness.
• To investigate variations in keratin modulus along the rachis, between feathers, and across species.

Main Methods:

• Tensile tests on compact keratin from eight bird species.
• Dynamic bending tests on swan primary feather rachises.
• Analysis of modulus variation with position, frequency, and temperature.

Main Results:

• Keratin moduli were similar across most species (mean E=2.50 GPa), except for the grey heron (E=1.78 GPa).
• No significant modulus differences were found in keratin from primaries 7-10.
• Keratin modulus increased distally along swan rachises and varied with frequency and temperature, but these changes were small.

Conclusions:

• Feather keratin's material properties show minor variations across species, positions, frequencies, and temperatures.
• The flexural stiffness of the rachis is primarily determined by its cross-sectional morphology, not keratin's material properties.