An experimental study of the impact of feral swamp buffalo Bubalus bubalis on the breeding habitat and nesting success of magpie geese Anseranas semipalmata in Kakadu National Park Original Research Article

The impact of buffalo Bubalus bubalis grazing and trampling on magpie goose Anseranas semipalmata breeding habitat and nest numbers was studied over nine wet seasons (1980–1988) at Kapalga within Kakadu National Park. Aerial photographs provided data to compare nest densities within six vegetation types in an area where buffalo grazed throughout the study with an area where buffalo were removed midway through. Buffalo had no significant effect on the abundance or distribution of vegetation types important to geese for breeding. However, high densities of buffalo suppressed the growth of several other species, particularly the grass Hymenachne acutigluma which increasingly displaced the deep water spike-rush Eleocharis sphacelata after buffalo were removed. The annual number of nests fluctuated between 7 and 2028, apparently in response to rain. Most nests were built in the spike-rush/wildrice Eleocharis spp./Oryza rufipogon association (71%) and in E. sphacelata (20%). Buffalo trampling and grazing influenced the location of nests but not number. After buffalo were removed, more nests were built in deep water areas at the forest edge of the floodplain.