Verspreiding en aantalontwikkeling van Nijlganzen Alopochen aegyptiacus in Noord-Drenthe en Midden-Groningen

September counts of flocking Egyptian Geese were conducted from the moment of settling in 1980 in the Gorecht, an area south of the city of Groningen (Fig. 1). This area turned out to be the core area for the species in the whole provinces of Groningen and Drenthe for at least up to 2002. Numbers increased annually with a mean of 43% from 1980 through 1994 (Fig. 2) and since then remained stable. The levelling off may be caused by a drop down in reproduction, since during the last years few young birds were observed. In April-May 2005 the area was populated by 400 individuals of which 250 were supposed to be paired (pairs or single birds indicating an incubating partner). In September in the same area 16 pairs (13%) were accompanied by fledglings (5x1,2x2,1 x3,3x4, 2x5,1 x6, 1 x7 and 1 x8). This results in 3.4 young/successful pair, 0.44 young per pair and 0.13 young per adult individual in the spring population. It is hard to believe that such low reproduction figures may lead to further population growth. Since 1994, when the numbers had stabilised, the distribution changed considerably (Fig. 3 and 4). The concentration of birds in the western part gradually vanished, whereas numbers in the east increased. Probably this change in distribution is due to local disappearance of protein rich grasslands that were turned into nature reserves in the course of the study. The low productive and highly structured meadows provide less profitable foraging grounds for the geese. Around 1 995 outside the core area hardly occurred Egyptian Geese, In spring 2005 368 individuals were counted outside the core (46% of the population). Most of these birds were seen in the vicinity of the core area (Fig. 2). Probably this has to do with the commitment of the species to open brook valleys and grassland on peat soils that are largely absent in the rest of the area.