Conservation challenges in mobile birds: What do we know and need to know for effective conservation of endemic inland migrants?

In New Zealand, intensive, site-based conservation management of bird species is often focused on controlling threats from invasive species at a local scale. Such management may benefit species resident within the site but may be insufficient for mobile taxa whose movements extend beyond it through annual migrations, irregular nomadic movements, or exchanges of dispersing individuals in metapopulation networks. Here we highlight challenges in the conservation management of mobile species, and argue that information on population trends, vital rates (recruitment, survival, and immigration or emigration), movements, and population connectivity is required to understand whether threats at a particular time or place result in population limitation, and to evaluate different management options. We review and synthesise current knowledge on the vital rates of a group of migratory wading birds endemic to New Zealand: pohowera/banded dotterel (Charadrius bicinctus), tarāpunga/black-billed gull (Larus bulleri), tarapirohe/black-fronted tern (Chlidonias albostriatus), tōrea/South Island pied oystercatcher (Haematopus finschi), and ngutu parore/wrybill (Anarhynchus frontalis). We identify knowledge gaps for these species about population trends, connectivity, and movement, and show that information on egg and chick survival is available for all species, but information on adult survival rates is scarce and only available for three species. Because dispersal and migration dynamics link geographically distant sites, greater recognition of population dynamics dependent on the full annual cycle is required to improve conservation actions and robustly assess management outcomes. We discuss how ecological understanding and conservation of mobile species can be advanced by technological developments coupled with new integrative modelling frameworks that incorporate existing data.