A review of Curlew headstarting projects in Europe

Headstarting is a relatively new, but increasingly popular, tool in wader conservation, whereby captive rearing and release is used to boost the breeding productivity of declining populations. Here, we use questionnaire and datasheet responses to review the major components and outcomes of 11 Eurasian Curlew Numenius arquata headstarting projects from five European countries. This provides an overview of current understanding, assessing the potential of headstarting as a conservation tool and identifying knowledge gaps. Headstarting projects were generally established to increase the size and/or breeding productivity of a wild Curlew population. Methods of egg collection and chick rearing varied between, and often within, projects. Projects collected a minimum total of 2,419 eggs between 2014 and 2023, of which 1,733 hatched and 1,298 chicks were released. The mean annual hatching rate across projects was 0.73 (± 0.21 SD) and the mean annual release rate of hatched chicks was 0.77 (± 0.19 SD). All projects reported health and development issues in some chicks, which varied in severity and type. Projects generally kept cohorts of < 15 chicks in a pen at the release site for at least one week before releasing into habitats ranging from farmland to wetland, usually located < 1 km from wild breeding waders and with potential to encounter wild Curlews. All projects colour-ringed chicks and eight deployed GPS tags. A total of 107 chicks of the 1,048 chicks released before 2023 were known to be alive after one year, and 36 were known to have nested. Only three projects used dedicated surveys specifically designed to monitor headstarted Curlews in the years post-release. Headstarting can be a highly effective tool for boosting Curlew egg and chick survival, however, post-release survival and recruitment are poorly understood. Collaborative meetings, reviews, formal analyses, increased monitoring effort and long-term commitment of resources are crucial to evaluate the potential of current and inform the development of future headstarting projects.