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The repayment hypothesis predicts that reproductive females in cooperative breeding systems overproduce the helping sex. Thanks to well-documented examples of thispredicted sex ratio bias, repayment has been considered an important driver ofvariation in sex allocation patterns. Here we test this hypothesis using data onpopulation brood sex ratios and facultative sex allocation from 28 cooperativelybreeding bird species. We find that biased sex ratios of helpers do not correlate withproduction biases in brood sex ratios, contrary to predictions. We also test whetherfemales facultatively produce the helping sex in response to a deficiency of help (i.e.when they have fewer, or no helpers). Although this is observed in a few species, it isnot a significant trend overall, with a mean effect size close to zero. We conclude that,surprisingly, repayment does not appear to be a widespread influence on sex ratios incooperatively breeding birds. We discuss possible explanations for our results, andencourage further examination of the repayment model

Sex Allocation Patterns across Cooperatively Breeding Birds Do Not Support Predictions of the Repayment Hypothesis