9623836 Rubenstein Every spring approximately 2.4 billion birds from 185 species migrate from their African wintering grounds to breed in the Palaearctic. The migrants are members of 185 species and the majority are small insect eating passerines. Long distance migration in small passerines is physiologically intriguing because it combines elements from two disparate physiological states: fasting and high aerobic exercise. This project will use Old World warblers (Sylviidae) as a model to study the fuel use and protein conservation of long-distance vernal migrating passerines. Short, medium and long distance migrants (Sylvia spp) will be captured mid-migration in Sede Boker, Israel. Variation in fuels used in flight and protein catabolism will be correlated with the effects of energy reserves and migration distance. This project promises to add new levels of understanding to exercise physiology, fasting biology and migration physiology and promises to broaden our understanding of how these processes can work in concert.