Meeting Abstract

S1-4.9  Jan. 5  Barbs of a Feather Bend (and Twist) Together JOHNSON, A.S.*; ELLERS, O.; BUTLER, M.; Bowdoin College, Maine

We propose the following design principle for feather barbs. By being thicker-walled dorso-ventrally, their flexural stiffness is increased during flight; but by allowing for twisting when loaded with dangerously high forces they firstly avoid failure by bending and secondly avoid complete failure by buckling rather than rupturing. Dorsal-ventral thickening of feather barbs is required to achieve sufficient flexural stiffness to support normal wing loads. However, if this high flexural stiffness were accompanied by high torsional stiffness, there would be a greater risk of catastrophic failure by rupture. Low torsional stiffness permits twisting and, because barbs are usually tall, narrow, thin-walled beams, a twisted barb can bend in a way that effectively sheds high forces. Furthermore, because it is laterally thin-walled, forces that are sufficiently large to lead to failure would cause failure by buckling rather than by rupture. Buckling is likely to be less catastrophic to barb function as it usually leaves an intact but weakened barb and, therefore, a barb that still functions almost as well as before buckling. This interpretation is supported by analysis of breaking and bending patterns of Osprey feather barbs.