Mechanical properties of bat wing membrane skin
Journal of Zoology (1996) 239: 357-378
S.M. Swartz, M.S. Groves, H.D. Kim and W.R. Walsh

The skin of the bat wing is functionally unique among mammals; it serves as a major locomotor organ in addition to its protective and regulatory functions. We used tensile testing to investigate the mechanical capabilities of wing membrane skin, and compared stiffness, strength, load at failure, and energy absorption among specific wing regions and among a variety of bat taxa. We related these characteristics to the highly architectural fibrous supporting network of the wing membrane. We found that all material properties showed a strong anisotropy. In particular, wing membrane skin shows maximum stiffness and strength parallel to the wing skeleton, and greatest extensibility parallel to the wing's trailing edge. We also found significant variation among wing regions. The uropatagium (tail membrane) supported the greatest load at failure, and plagiopatagium (proximal wing membrane between lateral body wall and hand skeleton) is the weakest and most extensible part of the wing. We believe that the increased load bearing ability of the uropatagium relates to its key role in capture of insect prey, and that the great extensibility of the plagiopatagium promotes development of camber near the wing's centre of lift. In interspecific comparisons, energy absorption and load to failure were greatest in Artibeus jamaicensis, the largest bat in our sample and the species with the highest wing loading, suggesting that wing loading may play a role in dictating the functional design of wing membranes.