Hoe groot is de invloed van Nijlganzen Alopochen aegyptiacus op het broedsucces van roofvogels?

Egyptian Geese are opportunistic breeding birds, using all kinds of nest sites at varying heights (0- 50 m) and egg-laying from February to August. The species readily usurps nests of raptors, as shown in a study area along the river IJssel near Zwolle (central Netherlands). In 1999 three Goshawk pairs Accipiter gentilis bred successfully in the study area. In March 2000 two of these nests were occupied by Egyptian Geese. The respective Goshawks had built new nests nearby and successfully raised fledglings. The third Goshawk pair used their old nest which contained 10 eggs on 22 April: 7 eggs of an Egyptian Goose and 3 eggs of its own. The goose eggs were removed by the author. The Goshawk eggs failed to hatch; embryonic development was apparently cut short by insufficient heat transmission during incubation of the 10 eggs. In the same area, 8 nests of Common Buzzards Buteo buteo were occupied by Egyptian Geese. Of these nests, four had been disturbed by human activity during the early stages of Buzzard occupation, after which Egyptian Geese took over. The other four nests had not been claimed by Common Buzzards in 2000. Interspecific aggression between Buzzards and Egyptian Geese was not observed. Egyptian Geese also bred in two nestboxes for Kestrels Falco tinnunculus. At one of these sites an extra nestbox was supplied and immediately used by the displaced Kestrels. The goose eggs in the second nestbox were removed; the displaced Kestrel pair re-occuped this site and bred successfully.