In many species, embryos are exposed to maternal hormones in utero, in the egg, or in the seed. In birds, mothers deposit substantial testosterone into their eggs, which enhances competitive ability of offspring. These maternal testosterone concentrations vary systematically within clutches in different patterns and may enable mothers to adaptively fine-tune competitive hierarchies within broods. We performed a comparative analysis to investigate this hypothesis using a broad set of avian species. We expected species with small size differences among siblings (arising from small hatching asynchrony or slow growth rates) to aim for survival of the whole brood in good years and therefore compensate last-hatching eggs with relatively more testosterone. We expected species with large size differences among siblings (large hatching asynchrony or fast growth rates) to produce surplus young as insurance against failed offspring and to facilitate elimination of redundant surplus young by bestowing last-hatching eggs with relatively less testosterone. As predicted, we found that maternal testosterone compensation to last-hatching eggs is stronger when size differences among siblings become smaller. Maternal testosterone compensation to last-hatching eggs also correlated negatively with hatching asynchrony and growth rates. These findings provide evidence for correlated evolution of several maternal effects that together support different maternal reproductive strategies. ; 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 ...