POSTPRANDIAL URINE LOSS AND ITS RELATION TO ECOLOGY IN BROWN LONG-EARED (PLECOTUS-AURITUS) AND DAUBENTONS (MYOTIS-DAUBENTONI) BATS (CHIROPTERA, VESPERTILIONIDAE)

Urine loss, over the first 12 hours after feeding, was positively and linearly dependent on food consumption in water-denied, brown long-ear ed bats (Plecotus auritus) and also in water-denied and water-provided , Daubenton's bats (Myotis daubentoni). The slope of the relationship (food-dependent urine loss) (363 mu l.g dry mass food(-1), S.D. = +/-7 0, n = 19) was not significantly different between the two species but predicted urine loss at zero food consumption (food-independent urine loss) was significantly lower in P. auritus (0.048 mu l.min(-1), S.D. = +/-0.015, n = 12) than in M. daubentoni (0.217 mu l.min(-1), S.D. = +/-0.040, n = 7). The same results were apparent if the data for M. d aubentoni were restricted to water-deprived animals only. Of total uri ne loss, 46% occurred in the first hour after feeding in M. daubentoni compared with only 20% in P. auritus. We suggest that the differences between the two species in the pattern of postprandial urine loss ref lect their relative association with open water when foraging and roos ting in the wild. In the course of the water-denied experiment, M. dau bentoni lost 15% of pre-fed body mass and showed signs of severe dehyd ration, while P. auritus only lost 6% and did not. However, urine loss only accounted for 8-10% of body mass loss. A water budget model for wild P. auritus in the summer was developed and suggested that if bats did not drink, approximately 19% of water loss would be attributable to faecal water loss, 18-20% to urine loss, and 59-62% of intake would be available to support evaporation and reproductive losses.