Monitoring population change using ’citizen science’ data: case study of the Hungarian White Stork (Ciconia ciconia) population between 1999 and 2021

Abstract In Hungary, changes in the White Stork population are monitored using two methods that involve a large number of volunteers: nest surveys since 1941, and since 1999 within the framework of the Common Bird Monitoring Scheme (MMM) programme. In our article, we briefly present the results of the nest survey data between 1999 and 2021, the population trend calculated on the basis of them, and the comparison of the latter with the trends shown by the MMM programme, which – among other species – counts all stork individuals on 2.5×2.5 km sample areas. Both sets of data show a decreasing trend, but there is a significant difference between them, which may be partly due to the inaccuracies of the nest database, considering the fact that the MMM also counts non-breeding adult and immature individuals. However, both methods have the characteristics that make them suitable for monitoring population trends.