3. Feeding and metabolic consumption
During daylight hours of thermal opportunity, individuals were assumed to forage when gut content was less than the maximal gut space (Table S1). Every hour, we calculated the maximal amount of ingested energy using an established foraging-energetic model (Function S1). The actual hourly ingested energy was limited by gut space (maximal gut space – gut content; KJ), which was updated every hour accordingly. Maximal daily digestion was calculated as a function of thermal opportunity hours (Function S2). At the end of each day, we calculated daily digestion rates and gut content, and updated gut space by reducing digested energy from gut content.
Metabolic consumption was determined by body mass, body temperature and activity state. First, we calculated hourly resting metabolic rate (RMR) according to an established function (Function S3). We multiplied the resting metabolic rate by 1.5 during the thermal opportunity hours when there was food in the gut but no foraging occurred (Roe et al.2005) to account for the energetic cost of digestion. During foraging hours, we multiplied the resting metabolic rate by 2 to account for the energetic cost of activity (Bennett 1982). Finally, we calculated hourly net energy budget of non-reproductive females by subtracting metabolic consumption from digestion. For non-gravid mothers and offspring, we multiplied hourly energy budget of non-reproductive females that are larger than zero by 0.79 (conversion efficiency; Table S1), because we assumed these individuals were storing gained energy (digested energy – metabolic consumption) as fat. We assumed gravid mothers invested all gained energy (hourly energy budget of non-reproductive females that are larger than zero) into reproduction (with no conversion efficiency) (Levy et al. 2016b, 2017).