In a coastal region of Venezuela the daily energy expenditure (DEE) and water turnover of the flower visiting bat Anoura caudifer was measured by using the doubly labeled water method. In flower visitors, this method allows independent measurement of energy intake and expenditure if the animals drink no additional water and if the nectar's energy content is known. An average DEE of 12.4 kcal/d and water exchange of 13.4 ml/d were found. Our data show a balanced energy budget when animals in the field imbibe nectar with a sugar concentration of 18–21%, which is roughly medial in the range of nectar concentrations of various bat flowers. The energy turnover of flower visiting bats is high compared with DEEs of other bat species, small mammals and birds; flower visiting bats seem to belong to those species having a fast spin of the life motor.