Adaptive sex ratios and parent–offspring conflict

Studies testing the theoretical prediction that birds would adaptively vary the sex ratio of their offspring either supported theoretical predictions or simply found a 1:1 sex ratio. Four recent papers, in particular one by Kate Oddie, of Great Tit nestling sex ratios, however, found that, when conditions are poor, the sex ratio is male biased, opposite of what was predicted by theory. The development of molecular markers to sex birds using minute amounts of blood has allowed experiments that help us to explain this apparent anomaly.