With its 4,800 hectares, the Lac du Der has become, over the years, a stopover for all migratory birds from Northern Europe and Siberia. Every year, between 200,000 and 300,000 Common Cranes (Grus grus) stop on the banks of the nature reserve, particularly around the port of Nuisement. Bewick’s Swan (Cygnus columbianus bewickii) spends its winters here from October to March. The climate is milder here than in its native Arctic tundra. In total, the LPO Champagne-Ardenne (League for the Protection of Birds) monitors over 310 species.