Effective butterfly conservation is built on five pillars: where are they, how is their trend, what are the drivers, which measures should we take and how can we communicate this knowledge to the relevant stakeholders and the wider public. This thesis focuses on the first three pillars and shows how citizen science and modern modelling techniques provide allow us to assess the distribution of butterflies. From this we can obtain the distribution trend, but also gain insight on the underlying mechanisms: persistence and colonisation. In the Netherlands, the fragmentation of the landscape has led to a decline in colonisation, making it more difficult for butterflies to establish in new habitat patches.
Since 1990 butterfly monitoring has provided us with a wealth of detailed population data. From these abundance changes, we can build important indicators for nature conservation, such as the European Grassland Butterfly Indicator. This indicator shows that since 1990 characteristic butterflies of grasslands have declined by 50%. Main causes for this decline are the intensification of agriculture in Western Europe, and abandonment in Eastern and Southern Europe. Butterflies are also sensitive to climate change. Another indicator, the Climate Change Indicator, shows that butterfly communities change to include more southern ‘warm’ species as compared to northern ‘cool’ species.