Establishing Elemental Turnover in Exercising Birds Using a Wind Tunnel: Implications for Stable Isotope Tracking of Migrants

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[edit] Author(s)

  • Hobson, K. A.
  • Yohannes, E.

[edit] Journal

Canadian Journal of Zoology-Revue Canadienne De Zoologie 85.6 (2007): 703-08.

[edit] Keywords

warblers sylvia-borin carbon isotopes metabolic-rate dietary tissues fractionation nitrogen flight migration c-13

[edit] Abstract

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. Contrary to expectation, delta C-13 values in blood did not follow an exponential model of growth to a plateau under the new diet. Instead, the best fit was a linear increase in delta C-13 value of the blood cellular fraction following the switch (day 15) until day 50, after which no further isotopic change was noted. We found no difference between experimental and control groups in the rate of carbon turnover. Our results support the contention that metabolic costs of migratory flight in conditioned birds may not result in increases in carbon elemental turnover in tissues and that previous estimates of tissue isotopic turnover based on captive, nonexercised birds may be applied to wild birds.

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