Meeting Abstract
Migratory birds dramatically increase the size of flight muscles in preparation for migration. However, we know very little about how migratory behavior influences bone morphology, even though bone and muscle are known to experience both mechanical and endocrine crosstalk. To determine the effects of migratory behavior on skeletal morphology and biomechanics, we analyzed specimens of both migratory and resident Dark-Eyed Juncos (Junco hyemalis) collected during breeding season. We obtained micro-computed tomography scans of the humeri and femora to separate the influence of mechanics (higher number of loads per day) from that of putative systemic changes (hormonal changes impacting bone morphology in preparation for migration). Our preliminary results in males show that migratory birds have a higher humerus width relative to resident birds, resulting in an increase in the ability to withstand the bending and torsional forces applied in flight. There was no difference in bone width of the femur. These results suggest that the humerus is altered to handle migration, but do not discern whether the mechanism is by increased wingbeats per day or by an increased force applied by the larger muscle. We are still performing analyses on trabecular (spongy) bone morphology and bone density. Further, analyses of an altitudinal migrant supspecies of J. hyemalis will enable us to tease apart the potentially confounding effects of migration and mass on bone morphology. Increasing our understanding of how migration influences bird bone morphology will clarify the evolution of morphological plasticity and migratory behavior.
