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).