Meeting Abstract
The size, shape, and distribution of feathers are important indicators of differences in flight adaptation among birds. Comparatively less is known about the role that feather mechanical properties play in flight. Penguins have transitioned from aerial to aquatic flight and have highly modified feathers that are thought to be adaptations to an extreme environment and the viscous fluid through which they fly. Thus penguin feathers offer an interesting test case for feather hydrodynamic and thermodynamic adaptations. Previous research has compared feather rachis stiffness in a range of avian taxa to quantify the variation in bending and tensile properties. Here we extend these studies to include penguin wing feathers. To study the effects feather specialization has on mechanical properties of the rachis, we conducted tensile tests of wing feathers from five penguin species. Whole feathers (n = 2-10 per species) were dissected free of the flipper connective tissues, secured by grips, and loaded in tension cyclically and then to failure. Raw load and displacement curves were converted to stress-strain curves. Young’s modulus was calculated both from external caliper measurements and from the cross sectional area based on histological sections of the penguin rachises. These tensile tests reveal that the moduli of feather rachises in the penguin species studied fall within the range of moduli found in previous studies testing tensile rachis stiffness in other avian taxa. Despite extreme modifications of penguin feathers, including increased homogeneity and thermodynamic insulation, the mechanical properties of penguin flight feather rachises are indistinguishable from those of other birds. These results indicate that feather morphology, specifically the reduced rachis length and overlapping orientation, may play a greater role in the transition to underwater flight than a change in material properties of the feathers themselves.
