Does hatch date set the clock? Timing of post-fledging movements for families of a colonially breeding, long-distance migratory songbird

Factors that influence the development of migration timing in juvenile songbirds have implications for the ability of individuals to respond positively to rapid environmental changes. We investigated the impacts of nest timing on the post-fledging movement timing of juveniles and adults of a migratory songbird. We tested whether first egg date and environmental factors predicted the initiation of post-fledging stages: fledge date for juveniles, and colony departure date for both adults and juveniles. At breeding colonies of purple martin (Progne subis) in southern Ontario, Canada, we monitored nests to determine the date of nest initiation (‘first egg date’) and deployed 122 coded radio-frequency tracking tags on young and adults to determine the timing of post-fledging stages. We found that first egg date, the number of nestmates and age of parents were the main predictors of fledge date. Of these three factors, only first egg date was carried through post-fledge to influence colony de...