Data on life history variables and their sources.

Data on life-history variables used in this study (data in bold, reference codes not in bold). Hatching spread represents the number or days between the hatching of the first egg and the last egg of a clutch. Days between eggs represents the time interval between the laying of subsequent eggs. Logistic growth rate constant represents the rate of mass increase in a sigmoid curve fitted to chick growth curves. % size difference was calculated as the mass of the core nestlings (estimated from their growth curves) at the time the last marginal chick hatched (hatching spread), divided by the size of a newly hatched chick. This represents the initial proportional size advantage of core chicks over marginal chicks.