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Fuel use and metabolic response to endurance exercise: a wind tunnel study of a long-distance migrant shorebird
1 Swiss Ornithological Institute, CH-6204 Sempach, Switzerland
2 Department of Animal Ecology, Lund University, Ecology Building, S-22362
Lund, Sweden
3 Netherlands Institute for Sea Research (NIOZ), PO Box 59, 1790 AB Den
Burg, Texel, The Netherland
4 Centre for Ecological and Evolutionary Studies, University of Groningen,
PO Box 14, 9750 AA Haren, The Netherland
5 Centre for Isotope Research, Nijemborgh 4, 9747 AG Groningen, The
Netherlands
* e-mail: susi.jenni{at}vogelwarte.ch
Accepted 20 May 2002
This study examines fuel use and metabolism in a group of long-distance migrating birds, red knots Calidris canutus (Scolopacidae), flying under controlled conditions in a wind tunnel for up to 10 h. Data are compared with values for resting birds fasting for the same time. Plasma levels of free fatty acids, glycerol and uric acid were elevated during flight, irrespective of flight duration (1-10 h). Triglyceride levels, the estimated concentration of very-low-density lipoproteins (VLDLs) and ß-hydroxybutyrate levels were lower during flight, while glucose levels did not change. In flying birds, plasma levels of uric acid and lipid catabolites were positively correlated with the residual variation in body mass loss, and lipid catabolites with energy expenditure (as measured using the doubly labelled water method), after removing the effect of initial body mass. The plasma metabolite levels indicate: (i) that the rates of catabolism of lipids from adipose tissue and of protein are higher during flight; (ii) that low ketone body concentrations probably facilitate fatty acid release from adipose tissue; (iii) that low triglyceride and VLDL levels do not indicate the use of an additional pathway of fatty acid delivery, as found in small birds; and (iv) that the relationships between energy expenditure, body mass loss and metabolic pattern suggest that a higher individual energy expenditure entails a higher rate of catabolism of both lipids and protein and not a shift in fuel substrate.
Key words: bird, flight, red knot, Calidris canutus, plasma metabolite, energy expenditure, lipid catabolism, protein catabolism, migration
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