Nitrogen and Energy Balance of the Fruit Bat Rousettus aegyptlacus on Natural Fruit Diets

Abstract

The nitrogen and energy balances of the Egyptian fruit bat, Rousettus aegyptiacus (Pteropodidae), were determined in a series of studies of animals on five single-fruit diets differing in their nutritional content (carob, Ceratonoia siliqua; Persian lilac, Melia azedarach; loquat, Eriobotrya japponica; mulberry, Murus nigra; and sycamore, Ficus sycomorus). It was found that except for Persian lilac, these fruits, which are eaten in nature by the bats, can adequately supply their nitrogen requirements, while Persian lilac and loquat were insufficient for their energy demands. On the basis of average nutrient composition across the tested fruits, the Egyptian fruit bat (mean body mass 144 g) requires a mean intake of 6g dry matter per day for maintaining nitrogen balance, while a mean intake of 11 g dry matter per day is needed in order to fulfill its daily energy requirements. These results suggest that energy, rather than nitrogen, is the limiting nutritional component in the diet of the fruit bat. The maintenance nitrogen requirement determined from the balance studies, 0.247 g N kg-0.75 d⁻¹, is 55% lower than expected from allometric relations. When the lilac diet is excluded, it is even lower: 0.110 g N kg-0.75 d⁻¹ (76% lower than expected). The maintenance nitrogen requirement is also much lower than reported for other species of fruit bats. This may reflect an adaptation to periods of low fruit availability and thus nitrogen shortage within the distribution limits of R. aegyptiacus.