Effect of Diet Composition on Plasma Metabolite Profiles in a Migratory Songbird

Plasma metabolites provide information about the physiological state and fuel use of birds, and have been used for predicting refueling rates of birds during migratory stopovers. However, little is known about the effect of diet on metabolite concentrations in small songbirds. We investigated the effect of dietary macronutrient composition on lipid and protein metabolites in captive White-throated Sparrows (Zonotrichia albicollis). Birds fed a high-protein, low-carbohydrate insect diet had lower plasma triglyceride concentrations and higher plasma B-hydroxybutyrate concentrations than birds fed a high-carbohydrate, low-protein grain diet during feeding. The insect-fed birds also had higher plasma uric acid concentrations than grain-fed birds and birds fed a low-protein, high-fat, and high-carbohydrate fruit diet. Diet did not significantly influence plasma concentrations of glycerol or nonesterified fatty acids. After subsequent overnight fasting, birds in all three diet groups had similar concentrations of lipid metabolites, but uric acid was marginally elevated in insect-fed birds. Given that dietary macronutrient composition affected certain plasma metabolite concentrations in sparrows, investigators should consider such diet effects when using these metabolites to estimate refueling rates of free-living migratory songbirds, particularly in species that exhibit dietary plasticity during migration.