Meeting Abstract

P2.77  Monday, Jan. 5  Variation in rachis cross-sectional geometry within and among flight feathers in the Barn Owl (Tyto alba) MIDDLETON, K.M.*; CONNERS, M.; SWARTZ, S.M.; California State University, San Bernardino; California State University, San Bernardino; Brown University kmm@csusb.edu

As the primary component of the avian aerodynamic lift generating surface, feather anatomy has been shaped by tradeoffs between mechanical and energetic constraints. Characteristics that would favor increased rigidity and resistance to buckling, stiffer material components and larger cross-sectional areas or second moments of inertia, are energetically more costly as these materials must be oscillated many times per second during flight. We studied variation in cross-sectional geometry of the rachis in both primary and secondary feathers of the Barn Owl (Tyto alba). Feathers were sectioned at five different locations along the length of the rachis either with a low-speed saw after embedding in epoxy or with a scalpel. Cross-sections were photographed under a dissecting microscope, and cross-sectional areas (XSA) and second moments of inertia (I) were calculated. Using published values for Young’s modulus (E) of feather keratin, we estimated flexural stiffness (E * I) at each location. All feathers exhibited a strong proximodistal gradient in both XSA and I, with commensurate decreases in flexural stiffness, with rachis tips approximately two orders of magnitude smaller than proximal ends. Between-feather variation correlated well with published values for aerodynamic pressures; distal primaries were stiffer than proximal primaries, which, in turn, were stiffer than secondaries.