Do females adjust the sex of their offspring in relation to the breeding sex ratio?

When the adult sex ratio differs between years in local populations, but st ill is predictable between adjacent years, it has been proposed that the be st strategy would be to bias the offspring sex ratio in favour of the rare sex. We tested this hypothesis using a data set of great reed warbler offsp ring, sexed by molecular techniques, that were collected over 11 breeding s easons at two adjacent reed marshes. Three important assumptions for this h ypothesis are fulfilled in the studied great reed warbler population. First , a substantial proportion of great reed warblers are living in small local populations where sex ratio distortions would be sufficiently large and co mmon. Second, breeding adults and their offspring return to breed in the lo cal population to a high degree. Third, females have a possibility to asses s the breeding sex ratio before laying their eggs. At our study site, the b reeding sex ratio was positively correlated between successive years. Howev er, contrary to our prediction, female great reed warblers seemed not to ad just their offspring sex ratio in relation to the local breeding sex ratio.