We used nitrogen isotope analysis from pectoral muscle of the Egyptian fruit bat Rousettus aegyptiacus (Chiroptera: Pteropodidae) to determine intrapopulation variation in sources of dietary protein throughout the year in northern Israel. In Mediterranean climates, winter and summer are stable seasons, whereas spring and fall are transitional seasons. Number of species of fruit-bearing plants is higher during the transitional periods, and we therefore predicted that intrapopulation variation would be higher during spring than in winter and summer; we made no prediction for fall because sample size was small. We also reconstructed sources of dietary protein for each individual using nitrogen isotope ratios (δ 15N) to determine whether individuals foraged on the same sources of food within each season. Intrapopulation variation in δ15N was significantly higher in spring (δ15N range: 9.7-17.5‰) compared to winter (8.8-11.1‰) and summer (9.5-11.2‰), suggesting that individuals during this period varied more in their use of protein sources. Dietary reconstruction revealed intrapopulation partitioning among the bats in the use of plant food items, and interspecific partitioning among plants in their dependence on dispersal by bats. © 2008 American Society of Mammalogists.