A range‐wide full‐annual‐cycle model informs conservation of a declining migratory shorebird

1. Untangling the spatial and temporal processes that influence the population dynamics of migratory species is challenging, because changes in abundance are shaped by variation in demographic rates across differing environments throughout the annual cycle. Population and demographic data available on migratory species are often fragmentary, providing only local, season-specific perspectives. To be effective, conservation strategies require range-wide, full-annual-cycle knowledge.
2. We developed a novel approach to link data from different segments of the population in a unified framework using stage- and season-specific population growth rates to assess population trends and conservation interventions for the New Zealand endemic migratory tōrea (South Island pied oystercatcher, Haematopus finschi). We combined demographic data collected at breeding and non-breeding sites between 1980 and 2022 in an integrated population model and population viability analysis to (a) determine population dynamics over time, (b) identify underlying drivers of change by estimating stage- and season-specific demographic rates and (c) evaluate future conservation interventions and interacting threats that are likely to primarily affect survival by comparing future population trajectories through a range of scenarios.
3. The tōrea population has been declining over the past 42 years by an average of 1.8% annually. Summer survival probabilities were generally higher than winter survival probabilities. Adult survival probability fluctuated less over time than the other demographic rates. Variation in population growth rates was most strongly associated with subadult winter survival (r = 0.29).
4. The population viability analysis showed that conservation interventions aimed at improving productivity would only be beneficial if survival probabilities remain at current levels. It is unlikely that additional mortality due to future, increased threats on survival can be offset by increased productivity.
5. Synthesis and applications. The tōrea population decline suggests the need for a higher IUCN threat classification and a conservation strategy (e.g. habitat protection and restoration) targeting multiple demographic rates across the annual cycle of tōrea. Our novel approach using population growth rates to link fragmented local, season-specific data to model range-wide full-annual-cycle dynamics has the potential to guide the conservation of migratory species where existing data are similarly fragmented.