ORIGINAL PAPER C. Korine á O. Zinder á Z. Arad Diurnal and seasonal changes in blood composition of the free-living Egyptian fruit bat (Rousettus aegyptiacus) Accepted: 5 February 1999 Abstract We studied the blood pro®le of the free-living fruit bat (Rousettus aegyptiacus) during the beginning of the activity period (around various feeding trees) and upon return to the day roost during 1994±1995. Results of the present study suggest that during winter and early spring bats are characterized by a poor physical and physiological state as re¯ected in the blood pro®le, revealing elevated urea and uric acid concentrations. It was found that at the end of the resting phase, R. aegyptiacus was in a mild state of dehydration (in- creased hematocrit and hemoglobin levels). At the end of activity, upon return to the day roost, both hem- atocrit and hemoglobin levels decreased but bats still maintained a high plasma osmolality. Several compo- nents in the blood are eected by the feeding time and show a cyclic change in concentration. The reverse re- lationship between glucose and triglyceride levels may indicate that glucose is the energy source during the active phase and that fat is the energy source during the resting period. The low cholesterol level in the blood re¯ects its absence in the fruit diet. Key words Blood biochemistry á Diet á Frugivore bats á Hematology Abbreviation BUN blood urea nitrogen Introduction Studies on the nutritional status of animal populations often use the animal's blood pro®le (hematology and chemical composition of the blood plasma) for evalua- tion of its physiological condition (Bjarghov et al. 1975; Nieminen 1979; Hellgren et al. 1988; Koopman et al. 1995; Dawson and Bortolotti 1997; Heard and Whittier 1997). The blood pro®le is aected by various factors such as age, gender and reproductive state, by endogenic rhythms of various metabolites, as well as by external factors such as season, time of the day, food availability and quality (Wesrhuyzen 1978; Hellgren et al. 1988; Wyk et al. 1993; Minematsu et al. 1995). Speci®c components in the blood may change when animals are exposed to cold and to low-quality food. For example, in response to energy and nitrogen short- age, blood urea nitrogen (BUN) and creatinine levels rise, while total nitrogen and albumin decrease (Nie- minen 1979; Hellgren et al. 1988; Alfaro et al. 1994; DelGiudice et al. 1994; Wolkers et al. 1994). Exposure to cold results in increased hematocrit and hemoglobin levels (Horton 1981; Lochmiller et al. 1985) and in in- creased triglyceride level (Alfaro et al. 1994). Other blood components that may change are cholesterol, as a function of the diet (Lenz et al. 1976; Carroll and Ku- rowska 1995; Widmaier et al. 1996; Heard and Whittier 1997), calcium (Wyk et al. 1993) and glucose, whose level changes with time after a meal (Westhuyzen 1978). Furthermore, the blood pro®le may also change due to stress, caused by capturing, handling and sampling the animal (Widmaier and Kunz 1993; Koopman et al. 1995). Studies of blood pro®le in the Chiroptera have mainly focused on hematological composition. It was found that bats are characterized by high hematocrit and hemoglobin levels compared with terrestrial mam- mals (Lewis 1977; Jurgens et al. 1981; Arevalo et al. 1987, 1992; Wightman et al. 1987; Viljoen et al. 1997). J Comp Physiol B (1999) 169: 280±286 Ó Springer-Verlag 1999 C. Korine (&) 1 á Z. Arad Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel O. Zinder Department of Medicine, Technion-Israel Institute of Technology, Haifa 32000, Israel Present address: 1 Smithsonian Tropical Research Institute, P.O. Box 2072, Balboa, Panama e-mail: korinec@gamboa.si.edu, Fax: +507-276-6823