6. Offspring survival
For each clutch/litter, the initial offspring numbers at hatching/birth were calculated by multiplying clutch size (Table S1) and developmental success. We calculated energy budgets of each clutch/litter of offspring by summing up hourly offspring energy budgets from the hatching/birth hour to the last hour of the year and multiplying it by the initial offspring number. We assumed all offspring contained the same amount of energy at hatching/birth (Table S1). At the end of the year, we calculated “offspring survival” by summing up energy budgets of all clutch/litters the mother produced:
\(V_{j}=\sum_{i=1}^{n}\left\{\par \begin{matrix}clu\_size*success*{{(E}_{j0}+E}_{j})\ \ ({E_{j0}>-E}_{j})\\ \text{\ \ \ \ \ \ \ \ \ }0\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ({E_{j0}\leq-E}_{j})\\ \end{matrix}\right.\ \) [Function 1]
where n was the reproductive frequency through a year, ‘clu_size’ was the clutch size, success was the developmental success, Ej0 was the initial energy storage of offspring, and Ej was the summed energy budget of individual offspring from hatching/birth to the end of the year.