RESUMEN
Digestion, absorption and assimilation of the meal are active processes that require start-up energy before the energy contained in a meal can be utilized. The energetic costs associated with feeding (specific dynamic action, SDA) are high in sit-and-wait foraging snakes that tolerate long fasting periods. We used (13)C-labelled prey to partition between endogenous energy sources (i.e. snakes' own resources) and exogenous energy sources (i.e. prey). A linear mixing model was then applied to determine the portion of (13)C originating from the different sources. The snakes showed a normal and typical postprandial response. By four hours after feeding, the delta(13)C-values indicated fuel switching from endogenous to exogenous. From then on, fuel mixing continuously increased until, at 20 h after feeding, 75% of fuel was exogenous. Resource partitioning showed that throughout SDA, the amount of exogenous energy increased to approximately 60% of SDA, which was equivalent to approximately 4.5% of the energy contained in a meal.