Launched in 2006 by the Muséum national d’Histoire naturelle in France, the Observatoire des Papillons des Jardins (OPJ) is a large-scale program where citizens are invited to identify and count butterflies in their garden, following a simple protocol. Its main aims are the long-term monitoring of common butterfly populations, and the assessment of the impact of gardening practices and broader-scale landscape on butterfly abundance and diversity. However, an important by-product is environmental education, as observers are prompted to see the impact of their gardening practices on common species. Since the beginning, more than 3500 gardens are monitored yearly all over the country, and 1.3 million abundance data have already been gathered for 28 species/species groups.

Results/Conclusions

Inter-annual abundance variations reach 80% for some species, but with three years of data only, it is too early to assess long-term trends of butterfly populations, and these variations can be linked with meteorology. However, it is already possible to study the impact of habitat modifications on butterflies: the abundance of all species but two is negatively correlated with the amount of artificial areas in the landscape, and the abundance of nine species is positively correlated with the amount of natural areas in the landscape. Both species which are not negatively impacted by urbanisation have peculiar ecological characteristics: Pararge aegeria has a nocturnal caterpillar feeding on several species of Poaceae which are well-established in disturbed areas. Cacyreus marshalli was accidentally introduced in Europe from South Africa. In France, its host-plant being ornamental Pelargonium, it is almost only found in gardens. The OPJ provides a unique opportunity to monitor in real time the expansion of this alien. The impact of local conditions on butterflies is monitored as well: observers are requested to briefly describe their gardening practices, and these data are significantly correlated with butterfly abundance and diversity. In particular, gardens with a high rate of pesticide use have significantly less butterflies than other gardens. These first results show the power of such observatories: when data are gathered by numerous non-specialist observers, monitoring can be done at a scale which would be impossible to reach with professional observers.