The relationship between timing of migration and reproductive success in an intra-tropical migratory bird

Migratory birds must undertake a number of key activities, including migration, breeding and molt to successfully reproduce and survive. Properly timing these events is key, because each is energetically costly and can result in significant fitness consequences. Spring migration, in particular is important for successful reproduction, because arriving early to the breeding area has many benefits, such as sexual selection and acquisition of a better territory. Therefore, we evaluated the relationship between arrival date and the reproductive outcome in Fork-tailed Flycatchers (Tyrannus savana). We worked at the Estação Ecológica de Itirapina, Brazil. We searched and banded adult flycatchers during the breeding season, beginning just prior to the arrival of flycatchers and finally, we monitored their nests at each site from construction until failure or fledging of nestlings. We found that flycatchers that arrived early to a tropical breeding site in South America have significantly higher reproductive success than those that arrive later. Overall, this result support the hypothesis that reproductive success of intra-tropical migrant flycatchers is related to their date of arrival on the breeding site. We found that male Fork-tailed Flycatchers arrived at the breeding site earlier than females, which to the best of my knowledge is the first documented evidence of protandry in an intra-tropical migratory passerine.