Establishing elemental turnover in exercising birds using a wind tunnel: implications for stable isotope tracking of migrants

Stable isotope measurements are being used increasingly to track migratory wildlife, especially birds. This approach relies on the assumption that tissue isotopic values represent a known period of dietary integration and that such a period is long enough to provide information on previous geographic origin. To date, such measurements have been obtained by switching isotopic composition of diets of sedentary captive individuals. The assumption has been that such measurements of elemental turnover likely represent minimal estimates, since wild migratory birds undergo increased metabolism and exercise during migratory flights. We tested this assumption using isotopic manipulation of diet on captive Rosy Starling (Sturnus roseus (L., 1758)) conditioned for flight in a wind tunnel. We used four control (no exercise) and four experimental (exercised) birds. For both groups, diet was switched from primarily a C-3 content to a C-4 content and blood samples were taken throughout our experiment until day 53. Contr...