BOWLIN, M.S.; WIKELSKI, M.C.; COCHRAN, W.W.; Princeton University; Princeton University; Illinois Natural History Survey: The relationship between individual morphology, atmospheric conditions, and inter-individual variation in heart rate and wingbeat frequency during natural migration in the Swainson�s Thrush (Catharus ustulatus)

Migratory flight, though less costly than early theoretical models predicted, still represents a significant investment in terms of energy and time for small passerines. We used ~1g radio transmitters to obtain continuous recordings of heart rate and wingbeat frequency during the nocturnal flights of 12 naturally-migrating Swainson�s Thrushes (Catharus ustulatus) in Illinois during spring migration. We found substantial inter-individual variation in average heart rate (12.06-14.81 Hz), average wingbeat frequency (10.25-11.75 Hz), and the difference between the two variables (1.50-3.84 Hz). Here we will present the results of a multiple regression analysis designed to determine whether or not this variation can be explained by variation in individual morphology, particularly wingtip shape and wingloading, and/or variation in the speed and direction of the winds the birds encounter during their migratory flights. If variation in individual morphology explains energy efficiency during migratory flight, it is likely that such variation could affect the overall speed of migration and determine arrival dates on the breeding grounds, which may in turn affect individual reproductive success and future survival.