Ecological constraints alone cannot explain delayed dispersal in splendid fairywrens

Delayed dispersal is a critical first step in the formation of both cooperative breeding and family-living groups. However, disentangling the multiple and potentially co-occurring factors that influence the dispersal of young individuals is often difficult and can require several data sources. We combine data from a long-term mark-recapture study and field experiments to address the patterns, fitness consequences, and proximate causes of delayed dispersal in the splendid fairywren (Malurus splendens melanotus). Splendid fairywren males remained as helpers more often, for more years, and settled closer to their natal territories than females. We found that the number of years males spent as helpers was positively correlated with persistence (a proxy for survival) within the population, illustrating a fitness benefit for delaying dispersal. By experimentally producing breeding vacancies for young males, we tested whether male-biased sex ratios and limited breeding opportunities constrained dispersal in this system. Only half of the vacancies created were filled, and dispersal took, on average, approximately three days. These findings illustrate that ecological constraints, benefits of philopatry, and life history may all be acting within the same system to shape dispersal patterns.