Vijf jaar dagvlindermonitoring in Nederland en Vlaanderen

Monitoring butterflies has been done by volunteers in the Netherlands since 1990 and in Flanders since 1991. An important aim of this project is to discover changes in numbers of the different species. This is described using the results of one species, the Gatekeeper (Pyronia tithonus), as an example. For most species it is now possible to determine an index which indicates the increase or decrease of a species. An index for rare species cannot be determined as the numbers are too small and unreliable. Ways to improve the monitoring of butterflies are discussed.