Natal dispersal likelihood is associated with population adult sex ratio in a cooperatively breeding bird

In cooperatively breeding species, sexually mature individuals often delay dispersal and become non-reproductive subordinates that help raise offspring. To understand how cooperative breeding can evolve, it is crucial understand the mechanisms driving delayed dispersal. Adult sex ratio (ASR) variation is often hypothesized to be an important evolutionary driver, although there is a lack of empirical evidence. Using a long-term dataset on the cooperatively breeding Seychelles warbler, we show that male juveniles are more likely to disperse when population ASR is female-biased. However, population ASR did not affect dispersal in female juveniles, indicating underlying mechanisms driving dispersal differ between the sexes.