Movements and activity characteristics of the Brown Booby Sula leucogaster during the non-breeding period

As the availability of individual-based tracking has increased, our understanding of seabird distributions outside the breeding season has advanced for a variety of species, but remains comparatively limited for species inhabiting the tropics. In this study, we investigated the at-sea movement and activity of eight Brown Boobies Sula leucogaster during the non-breeding period using light-level geolocators. Boobies spent the non-breeding season in the western Pacific across a large geographical range; however, at a regional scale, there was variation among individuals in their use of wintering habitats, with areas 6 575 km apart between their northernmost (the East China Sea/Yellow Sea) and southernmost (northern New Guinea) destinations. Overall, during the non-breeding period, boobies spent 17.6 % ± 5.0 % of their time on the water during the day and 11.1 % ± 8.2 % of their time on the water at night. This low percentage of time spent on the water at night indicates that they may have rested on land or roosted on rocks, a behavior that might be an anti-predatory strategy. Although individuals exhibited spatiotemporal variations in their movements, all tracked birds were absent in the breeding region for periods of time coinciding with seasonal pulses of unfavorable local environmental conditions. This study is the first to explore individual-based at-sea movements and activity characteristics of Sula species during the non-breeding period. Our results provide insight into how breeding phenology relates to seasonal movements.