Meeting Abstract

43.4  Monday, Jan. 5  Cross-sectional geometry of the forelimb skeleton and flight mode in pelecaniform birds SIMONS, E. L. R.*; O’CONNOR, P. M.; Ohio Univ, Athens; Ohio Univ, Athens er238604@ohio.edu

Pelecaniforms are a group of marine birds that vary greatly in body size, whole wing shape, and flight mode. Members of this clade utilize static (thermal) soaring (Pelecanus, Fregata), dynamic soaring (Morus), alternating flapping and gliding (Sula, Phaethon), and continuous flapping (Phalacrocorax). The objectives of this study were to investigate differences in cross-sectional geometry of the three main wing elements in birds that utilize different flight modes. The mid-shaft of the humerus, ulna, and carpometacarpus (CMC) from 16 species (n = 94) were microCT scanned at Ohio University. The following biomechanical parameters were derived for each element: CA/TA, the amount of cortical bone relative to total bone cross-sectional area; Imax/Imin, a shape ratio indicating resistance to bending; and J/L, length-standardized resistance to torsion. Results indicate that static soaring birds (Pelecanus, Fregata) exhibit lower CA/TA values in all three elements relative to dynamic soaring birds, flap-gliders, and flapping birds (p < 0.001). Phalacrocorax and Anhinga exhibit the largest CA/TA values, suggesting a possible link to buoyancy reduction. The static and dynamic soaring birds exhibit significantly higher J/L values than either flapping or flap-gliding birds (p < 0.001), suggesting a higher resistance to torsional loading. For all flight modes, the CMC exhibits the most elliptically shaped mid-shaft cross-section (high Imax/Imin values), suggesting that this element may be experiencing more bending loads. These results will be discussed in the context of whole wing shape and contrasted with selected procellariiform birds, a distantly related clade of seabirds characterized by a similar range of body sizes and flight modes.