Leveraging Large Scale, Open-Access Population Data to Calculate Genetic Indicators: A Continental Assessment of European Birds

Caroline C. Mouton, Bodine Leenders, Sean M. Hoban, Joachim Mergeay, Gernot Segelbacher, Julia Caroline Geue 

The Kunming-Montreal Global Biodiversity Framework (KMGBF) committed countries worldwide to conserving and restoring genetic diversity. Yet, translating complex genetic data into actionable metrics remains formidable for most stakeholders, especially when DNA-based data are unavailable. Proxy metrics such as the KMGBF headline indicator (A.4) using effective population size (Ne) and the complementary indicator on maintained populations (PM) can be assessed without direct genetic data. By bypassing the need for direct genetic sampling, these indicators offer an accessible, broad-scale framework for monitoring population genetic health and guiding policy decisions. This study provides a proof-of-concept for calculating genetic indicators for 187 bird species listed under Annex I of the EU Birds Directive. Using census and abundance data from Eionet (European Environment Information and Observation Network) and the European Breeding Bird Atlas, we developed a standardized pipeline for population delineation and indicator estimation, inferring Ne from census size (Nc) via different Ne/Nc ratios (0.1, 0.2, and 0.4). Results show that genetic indicator values for European birds are generally higher than those reported in multi-taxa studies, likely reflecting high avian dispersal. The proportion of Ne≥500 correlated strongly with EU IUCN Red List status, though some "Least Concern" species exhibited low values, highlighting cryptic genetic erosion. Additionally, long-distance migrants had higher effective population sizes than species with restricted occurrences. These overall results were consistent for all Ne/Nc ratios. By demonstrating that continental-scale genetic indicator assessments are feasible using open-access data, this study provides a scalable blueprint for countries to meet CBD reporting obligations, while offering policymakers a clear path to identify and prioritize species in need of genetic rescue. Specifically, species with low genetic viability should be prioritized for active management. Our findings underscore the importance of integrating ecological traits and dispersal dynamics into assessments of species’ long-term evolutionary potential.