The Distribution of the Nests of the Magpie Goose (Anseranas-Semipalmata Latham) at Kapalga, Nt - a 4-Year Study

Abstract

A survey of the distribution and abundance of nests of the magpie goose (Anseranas semipalmata Latham) was carried out over 4 years (1980-83 inclusive) at a site covering about 1000 ha on the South Alligator River floodplain at Kapalga, N.T. There were large differences in the number of nests built from year to year. Maximum water depth on the plains and the length of time the plains were flooded varied considerably from year to year and since these factors have an effect on the type and distribution of the vegetation, a study of the relationship between the density of nests, water depth and the vegetation present was made in each year. Breeding was confined to three recognisable vegetation types: (1) a mixture of spike rushes, Eleocharis spp., and wild rice, Oryza meridionalis; (2) pure stands of Oryza meridionalis; (3) pure stands of Eleocharis sphacelata. The density of nests was higher in areas of Eleocharis spp./Oryza meridionalis mixture than in E. sphacelata or 0. rneridionalis and in 3 years out of 4, more nests were built in deep water rather than shallow, while in the fourth year nests were built at intermediate water depths. Significant numbers of nests were built in the areas of Oryza meridionalis in only one year when the density of nests was greater in deep water rather than shallow.