© Marcel Burkhardt
Jenni, L. & S. Jenni-Eiermann (1998)
Fat and protein utilization during migratory flight.
In: Adams, N. & Slotow, R. (Eds), Proc. 22 Int. Ornithol. Congr., Durban, University of Natal
Non-stop endurance flapping flight in migrant birds may be limited by the amount of stored fuel or water that they carry. To maximise flight duration, most of the energy is derived from lipid stores. In order to adequately supply the active muscles with adipose tissue derived lipids during endurance exercise, small passerines utilise a specific metabolic pathway, and may have other unique means of fatty acid delivery. However, as in inactive birds during long-term fasting, flying birds also catabolise protein, which may also limit flight duration. Since amino acids have no special storage form (such as glycogen for carbohydrates and triglycerides for fatty acids), but serve specific functions, protein utilisation results in some functional loss. The few available data suggest that the relative contribution of energy derived from protein as a proportion of the total energy expenditure of birds during endurance flight is as low as that of inactive fasting birds. This means that the absolute amount of protein catabolism is elevated during flight, possibly in proportion to metabolic rate. The level of protein utilisation attained is negatively related to initial fat stores. These findings suggest that the ratio of fat to protein stored before, and used during endurance flight is important for maximising flight duration and should be included in models of optimal bird migration. Predictions are given about the ratio of fat to protein catabolised during flight as a function of the duration of non-stop flight and the risk of dehydration.