Data from: Within-clutch variation in yolk testosterone as an adaptive maternal effect to modulate avian sibling competition: evidence from a comparative study

The data package contains three datasets:
-Sources for yolk testosterone used in this study.
Mean yolk testosterone concentrations in core eggs, marginal eggs and the difference in yolk testosterone between core and marginal eggs. Marginal eggs represent the later-laid, asynchronously-hatching eggs and were identified by dividing the hatching spread by the laying interval between subsequent eggs (app. C). If these calculations produced non-integers, we rounded the values up. Core eggs represent the early-laid, synchronously-hatching eggs and were identified by subtracting the number of marginal eggs from the average clutch size. Yolk testosterone concentrations for core and marginal eggs were averaged to produce mean core T concentrations and mean marginal T concentrations, respectively. In our analyses, we included mean marginal T minus mean core T as a response variable and mean core T as a covariate that corrects for differences in average clutch T values across species as well as assay differences. * indicates the species excluded from analyses containing initial size asymmetries between core and marginal chicks as a predictor (n=28 species included). **indicates the species excluded from analyses containing hatching spread and logistic growth rate constant as a predictor (n=25 species included).

-Data on egg size and their sources.
Data on within-clutch variation in egg size used in this study. Marginal eggs represent the later-laid, asynchronously-hatching eggs and were identified by dividing the hatching spread by the laying interval between subsequent eggs. If these calculations produced non-integers, we rounded the values up. Core eggs represent the early-laid, synchronously-hatching eggs and were identified by subtracting the number of marginal eggs from the average clutch size. Sizes of core eggs and marginal eggs were averaged to produce mean core egg size and mean marginal egg size, respectively. In our statistical models, we included proportional difference in egg size between core and marginal eggs as a covariate. This was calculated by dividing the difference in egg size between core and marginal eggs (mean marginal size minus mean core size) by mean core egg size.

-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.