Effect of dietary fatty acid composition on depot fat and exercise performance in a migrating songbird, the red-eyed vireo

Most migrating birds accumulate lipid stores as their primary source of energy for fueling long distance flights. Lipid stores of birds during migration are composed of mostly unsaturated fatty acids; whether such a fatty acid composition enhances exercise performance of birds is unknown. We tested this hypothesis by measuring metabolic rate at rest and during intense exercise in two groups of red-eyed vireos, a long-distance migratory passerine, fed either a diet containing 82% unsaturated fat (82%U), or one containing 58% unsaturated fat (58%U). Vireos fed the 82%U diet had fat stores containing (77%) unsaturated fatty acids, whereas vireos fed the 58% U diet had fat stores containing less (66%) unsaturated fatty acids. Blood metabolites measured prior to and immediately following exercise confirmed that vireos were metabolizing endogenous fat during intense exercise. Mass-specific resting metabolic rate (RMR) was similar for vireos fed the 58%U diet (2.75 +/- 0.32 ml O-2 g(-1) h(-1)) and for vireos fed the 82%U diet (2.30 +/- 0.30 ml O-2 g(-1) h(-1)). However, mass-specific peak metabolic rate (MRpeak) was 25% higher in vireos fed the 58%U diet (28.55 +/- 1.47 ml O-2 g(-1) h(-1)) than in vireos fed the 82%U diet (21.50 +/- 1.76 ml O-2 g(-1) h(-1)). Such whole-animal energetic effects of fatty acid composition of birds suggest that the energetic cost of migration in birds may be affected by the fatty acid composition of the diet.