This observatory is part of the Vigie Nature network.

The methodology is simple and straightforward: observers who want to participate are randomly assigned a 2×2 km area within a 10 km radius around a location of their choice as well as an alternative area in the event that first area is inaccessible. They can also choose a site that is most convenient.

Inside the assigned area, the observer needs to set up 5 to 15 transects (paths) in a way that is consistent and proportional to the local habitats. He or she should then complete four counts each year, from May to August. All of the butterflies seen along the transects should be noted, and the habitat should be described according to a European classification system that has been adapted for France.

The butterfly and habitat surveys are repeated every year at the same points and same dates, weather conditions permitting, by the same observer. 

The program protocol is available on the website, along with various information on how to set up the program (including the list of local coordinators to contact to participate).