The Effect of Diet Composition on Migratory Fuelling in Garden Warblers Sylvia borin

Abstract

Prior to migration, many migratory birds accumulate large stores of lipids as the prime energy for their migratory flights. Although this phenomenon is well known, comparatively little is known about the mechanisms of fat accumulation, and the nutritional demands and nutritional adaptations of fattening migrants. This paper shows recent findings on the role of nutrients in fattening, and how migrants are likely to achieve optimal rates of fattening by diet selection. Dietary energy and nutrient composition of foods clearly influenced the rate of daily body mass gain during migratory fattening. However, it was neither energy nor a single nutrient alone which accounted for migratory fattening. Most of the variation in body mass gain was explained by the combined effects of high energy intake, where the energy was provided by fat, and by protein intake, whereas the role of carbohydrates is less clear. The data are discussed with respect to the adaptive role of seasonal shifts in diet selection during fattening periods known for many species, and the consequences of diet for fat deposition time, fat deposition rates, and fat loads at departure as major predictors in optimal migration models.