SMITH, S.B.*; MCWILLIAMS, S.R.; GUGLIELMO, C.G.; University of Rhode Island, Kingston; University of Rhode Island, Kingston; University of Western Ontario, London, Canada: Effect of diet composition on plasma metabolites in a migratory songbird

Plasma metabolites are sensitive indicators of fuel use in birds, and so they may be useful for assessing the physiological state of migrating birds in relation to habitat quality. However the direct influence of diet on plasma metabolites in small songbirds is unknown. To determine how diet composition affects plasma metabolite concentrations in songbirds, we measured lipid and protein metabolites in White-throated Sparrows (Zonotrichia albicollis) that were fed diets similar in macronutrient composition to natural fruits, insects, or grains. During feeding, plasma triglyceride was lower and plasma B-hydroxybutyrate was higher in insect-fed than grain-fed birds, and plasma uric acid was higher in insect-fed than both grain-fed and fruit-fed birds. After overnight fasting, plasma triglyceride and B-hydroxybutyrate were similar in all diet groups, and plasma uric acid was marginally higher in insect-fed birds. Diet had no effect on plasma glycerol or non-esterified fatty acids in fed or fasted birds. Our results suggest that dietary macronutrient composition can affect plasma concentrations of certain metabolites in songbirds. Thus, information about the nutritional content of food resources may be important when using metabolites to assess habitat quality for migrating songbirds because many species change their diet during migration.