The influence of meal size on the digestive energetics of Gould's wattled bat, Chalinolobus gouldii

Although variation in meal size is known to have an impact on digestive energetics, there is limited information on how it influences metabolic rate and energy assimilation in insectivorous bats. We investigated the influence of meal size, representing 10% or 20% of an individual's weight, on the digestive energetics of Gould's wattled bat, Chalinolobus gouldii (n = 61 bats). Using open-flow respirometry, we recorded a median resting metabolic rate of 2.0 mL g-1 h-1 (n = 51, range = 0.4-4.8) at an air temperature of 32°C. Median postprandial metabolic rate peaked at 6.5 (range = 3.4-11.6, n = 4) and 8.2 (range = 3.8-10.6, n = 7), representing 3.3-and 4.1-fold increases from resting metabolic rate for the two meal sizes. Using bomb calorimetry, we calculated the calorific value of the two meal sizes, and the calories lost during digestion. Following gut passage times of 120 min (range = 103-172, n = 15) and 124 min (range = 106-147, n = 12), C. gouldii assimilated 88.0% (range = 84.6-93.8, n = 5) and 93.3% (range = 84.0-99.4, n = 10) of the kilojoules available from the 10% and 20% meal sizes, respectively. When fed ad libitum, C. gouldii consumed a mean of 23.2% of their body weight during a single sitting (n = 18, range = 6.3-34.1%). Overall, digestive energetics were not significantly different between 10% or 20% meal sizes. The ability to ingest small and large meals, without compromising the rate or efficiency of calorie intake, indicates that free-ranging C. gouldii are likely limited by food available in the environment, rather than the ability to assimilate energy.