Transboundary priorities for protection of frigatebird non-breeding habitat in a heavily impacted region

Species that inhabit spatially-distinct regions at different stages of their lifecycle pose challenges to conservation managers, particularly when distributions span international or jurisdictional boundaries. Despite the importance of non-breeding habitat to the persistence of individuals and species, there remains limited information on the habitat requirements of many species during the non-breeding period. We used Global Positioning System tracking devices to determine the non-breeding movements of Great Frigatebirds, Fregata minor, and Lesser Frigatebirds, F. ariel, across much of Southeast Asia. These data were analysed with MaxEnt modelling to identify important habitat features for non-breeding frigatebirds and inform priorities for targeted conservation measures. Models with the greatest predictive performance were influenced strongly by bathymetry. Predicted habitat suitability was greatest in shallow waters. Similarly, warmer waters had greater predicted suitability during the wet season. We also identify 45 roosting sites that form an important component of the habitat used by non-breeding frigatebirds in this region. The existing marine protected area (MPA) network contains only a small proportion of habitat identified as suitable or optimum for non-breeding frigatebirds. This is of particular concern given that some parts of the region’s marine environment are among the most heavily human-impacted in the world. Our findings can be used to implement spatially-targeted conservation measures such as education campaigns focusing on bycatch reduction and subsidies for bycatch reduction methods (e.g., streamer lines) for fisheries operating in suitable and optimum habitat. They could also inform placement of additional MPAs to maintain habitat integrity in areas we identified as suitable or optimum habitat, particularly when these habitats occur in close proximity to roosting sites. Such approaches will likely provide benefits to frigatebird populations tracked in the present study as well as those dispersing to the study region from other ocean basins.