The small microchiropteran bat, Chalinolobus gouldii, undergoes large daily fluctuations in metabolic rate, body temperature, and breathing pattern. These alterations are accompanied by changes in surfactant composition, predominantly an increase in cholesterol relative to phospholipid during torpor. Furthermore, the surface activity changes, such that the surfactant functions most effectively at that temperature which matches the animal’s activity state. Here, we examine the surface activity of surfactant from bats during arousal from torpor. Bats were housed at 24 °C on an 8:16 h light:dark cycle and their surfactant was collected during arousal (28< T b <32 °C). Surface activity was examined with a Captive Bubble Surfactometer at 24 and 37 °C. Surfactant from arousing bats was more active at 37 °C than at 24 °C, indicated by a lower ST min and reduced film area compression required to reach ST min. It appears that the arousal-induced changes in surfactant composition, i.e., lower levels of cholesterol, inhibit adsorption of surfactant at 24 °C. Furthermore, the alterations in surfactant composition during arousal are very rapid, such that the mixture behaves more like surfactant from warm-active bats, and therefore, functions more effectively at 37 °C.