Gains and losses of French butterflies: tests of predictions, under-recording and regional extinction from data in a new atlas

New data appearing in the second of two French atlases within one and a half years confirm that there was substantial under-recording of butterfly species in France for the production of the first atlas, particularly in the south and west of the country. Under-recording is still a prominent feature of the southwest region and eastern border. The new data also reveal contractions in the ranges of 60 species suggesting real losses as a result of regional extinction especially in the north of the country. This finding links adjacent areas of ongoing high regional extinction in continental European Lepidoptera extending from the Netherlands through Belgium into northern France. The new data also demonstrate that predictions of species numbers and species incidences based on records in the first atlas, using regression techniques on geographical and neighbourhood variables, have been largely successful (76% correct prediction of new records for départements). This supports the application of such techniques to targeting surveys for mapping spatial units and species to improve atlas databases; the recent rapid changes in distributions underlines the importance of having a suitable framework for continuing recording after atlas publication.