Patterns of fuel use and storage in songbirds in relation to diet composition and food availability during migration

Susan B Smith, University of Rhode Island


Migration is energetically demanding for small songbirds and requires frequent stops to rest and replenish energy reserves. Food quality and availability at migration stopover sites may influence the length of time birds spend refueling, and could therefore be used to predict the quality of habitats for migrating birds. The objectives of my research were (1) to determine the effects of dietary macronutrient composition on plasma indicators of fuel use and body composition of birds, (2) to compare the nutrient composition and adequacy of seasonal fruit resources for satisfying the nutritional requirements of songbirds, and (3) to evaluate patterns of fuel use and storage in migrating passerines in relation to fruit availability at stopover sites in southern New England. ^ We found that diet-related changes in plasma triglyceride and B-hydroxybutyrate of captive White-throated Sparrows (Zonotrichia albicollis) were more strongly related to fat mass than lean mass of birds. Sparrows fed a high-protein diet had higher plasma uric acid. They also had higher plasma triglyceride and stored the most body fat when fed low-protein, high-carbohydrate diets, whereas they had higher plasma B-hydroxybutyrate and lower body fat stores when fed high-fat or low-carbohydrate diets, independent of energy intake. ^ Most fruits available to birds during autumn migration on Block Island, Rhode Island contained primarily carbohydrates and little protein and fat, although three fruits contained more fat and were most energy dense. Birds consumed high-energy fruits more than low-energy fruits, but they likely must also consume insects along with fruits to satisfy their protein requirements. Passerines that are more frugivorous during autumn migration had higher plasma triglyceride and lower B-hydroxybutyrate and uric acid compared to other less frugivorous species, though certain exceptions may be related to factors such as diet specialization. Hermit thrushes (Catharus guttatus) had higher plasma triglyceride on Block Island where abundance of high-quality fruits is high compared to a mainland site in southern Rhode Island where fruit availability is low. Our results suggest that diet should be considered when evaluating habitat quality for migrating songbirds and that certain plasma metabolites provide important information about species and site differences in fuel use and deposition. ^

Subject Area

Biology, Ecology|Biology, Animal Physiology

Recommended Citation

Susan B Smith, "Patterns of fuel use and storage in songbirds in relation to diet composition and food availability during migration" (2007). Dissertations and Master's Theses (Campus Access). Paper AAI3277015.