Energetics and Water Flux of Free-Ranging Big Brown Bats (Eptesicus fuscus) during Pregnancy and Lactation

Abstract

We used doubly labeled water to measure carbon dioxide production and water flux during pregnancy and lactation in free-ranging big brown bats, Eptesicus fuscus. Mean (±SE) carbon dioxide production was 1,749 ±144 ml/day during pregnancy (n = 16) and 2,770 ±351 ml/day during lactation (n = 5). Including estimates of tissue production and milk export, we calculated that the average requirement for assimilated energy was 48.9 and 105.1 kJ/day for pregnant and lactating females, respectively. About 2% of the total energy required during pregnancy was placed into fetal tissue; milk energy accounted for 28% of the energy assimilated during lactation. Daily water flux was 8.47 and 17.07 ml/day for pregnant and lactating females, respectively. We calculated that E. fuscus obtained >66% of its water preformed in the diet, but 20–22% of daily water intake was from drinking. Urinary water was the largest component of water efflux during pregnancy (72%) and lactation (56%); water exported in milk represented 22% of daily water efflux during lactation. Calculated evaporative losses for free-ranging E. fuscus were half those predicted from laboratory measurements.