Reproductive Energetics of Captive and Free‐Ranging Egyptian Fruit Bats (Rousettus Aegyptiacus)


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January 2004


This study explored how a flying frugivorous mammal, the Egyptian fruit bat (Rousettus aegyptiacus), meets the increased energy requirements of reproduction. This bat feeds on low‐protein fruit, and females have bimodal polyestrous cycles that are relatively long for a small mammal. We measured the energy and water balance of captive nonreproductive, pregnant, and lactating females, and of free‐ranging lactating females. Our results indicate that females use more than one strategy to cope with the high energy demands of reproduction. These strategies may change according to the availability of food and reproductive status. The primary strategy near the end of pregnancy and at peak lactation was increased food consumption. In the laboratory, mean metabolizable energy intake (MEI) of pregnant and lactating females (271 and 360 kJ/d, respectively) increased by 35% and 80%, respectively, compared to that of nonreproductive females (200 kJ/d). At peak lactation, energy intake measured by doubly labeled water averaged 350 kJ/d. During late pregnancy, water turnover rate (WTO) increased by 15–23% compared to that of nonreproductive females. In the field, WTO at peak lactation was 44% higher than in captive lactating females, and milk production was estimated to be 22 mL/d. Absolute resting metabolic rate (RMR) in late pregnancy was significantly lower than the RMR of nonreproductive females, suggesting that a metabolic depression was used as a compensatory mechanism. Fat deposition was evident during the second pregnancy, when food availability was high, presumably in preparation for a second lactation period. Fetal tissue represented ∼1.3% of the total energy assimilated during pregnancy, and the gross efficiency of lactation averaged 24%. Both values are lower than the values reported for other eutherian mammals, but similar to estimates for other bat species, and probably reflect the high energy costs associated with flight. A long lactation period may be constrained by flight and the low‐protein diet of fruits. We c


Egyptian Fruit Bat, Energy Balance, Fat Stores, Lactation Efficiency, Megachiroptera, Metabolic Depression, Reproductive Energetics, Rousettus Aegyptiacus, Water Balance

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Ecology, Vol. 85, no. 1 (2004).