Meeting Abstract

P2.111  Saturday, Jan. 5  Microstructure and cross-sectional shape of limb bones in Great Horned Owls and Red-tailed Hawks: how do these features relate to differences in flight and hindlimb usage? MARELLI, C.A.*; SIMONS, E.L.R.; Midwestern Univ.; Midwestern Univ. cmarelli64@midwestern.edu

The Red-tailed Hawk (RTH) and Great Horned Owl (GHO) are two species of raptor that are similar in body size, have generalized diets, and often occur sympatrically. The RTH is active during the day and the GHO is nocturnal. They also differ in primary flight style; the RTH uses static soaring and the GHO uses flap-gliding. Both species use their hindlimbs to catch prey, but the RTH uses rapid leg movements, whereas the GHO uses high force grip. The objectives of this study were to characterize the microstructure and cross-sectional shape of limb bones of these species and examine the relationship with flight and hunting behaviors. The mid-shaft of four limb bones (humerus, ulna, femur, tibiotarsus) from 6 individuals of each species was sampled and prepared histologically. The laminarity (proportion of circular primary vascular canals) and cross-sectional parameters (measure of the amount and distribution of cortical bone: cortical area, second and polar moments of area) were calculated. As predicted, the forelimb elements and femur in both species exhibit higher laminarity than the tibiotarsus. The humerus and femur also exhibit higher polar moment of area, suggesting a higher resistance to torsional loading. The tibiotarsus has a larger relative cortical area than other bones, suggesting better resistance to compressional loads. Between species, the laminarity of the RTH femur is higher than that of the GHO. The femur of the RTH is more circular and the tibiotarsus is more elliptical than that of the GHO. Although the species use different flight modes, the microstructure and shape of forelimb bones is quite similar. Differences among hindlimb elements may reflect different methods of capturing prey.