Water balance of free-ranging little brown bats (Myotis lucifugus) during pregnancy and lactation

(Uploaded by Plazi for the Bat Literature Project) This study provides the first measurements of daily water flux in free-ranging bats during pregnancy and lactation. We used the wash-out rate of tritiated water from the body water pool to calculate daily water flux in 10 pregnant and 14 lactating little brown bats (Myotis lucifugus). Average water influx was 6.16 ± 0.47 (SE) mL/day during pregnancy and 6.91 ± 0.37 mL/day during lactation; average efflux was 6.27 ± 0.44 and 7.07 ± 0.36 mL/day during pregnancy and lactation, respectively. Using data from the literature, we partitioned daily flux into major components. Our calculations indicated that most (> 62%) water influx was preformed water in the insect diet. Drinking water represented 23–26% of daily influx. Although previous studies indicated that evaporative losses greatly exceeded urinary losses in laboratory-maintained M. lucifugus, urinary and evaporative losses were comparable in our free-ranging bats. Urinary losses represented 46% of water efflux during pregnancy and 35% during lactation. Over 80% of all water efflux occurs during the 8-h night.