Distribution and Abundance of Brolgas and Black-necked Storks in the Alligator Rivers Region, Northern Territory

Abstract

Aerial surveys between 1981 and 1984 were used to identify monthly trends in the abundance of Brolgas Grus rubicundus and Black-necked Storks Ephippiorhynchus asiaticus on five floodplains of the monsoonal, subcoastal Northern Territory. Ground surveys were conducted during the same period on one of the plains, the Magela floodplain. Aerial surveys indicated that Brolgas were significantly more abundant in the dry season than the wet; they congregated particularly on the Cooper floodplain, were of intermediate abundance on the Magela and Nourlangie floodplains, and occurred only sporadically on the East Alligator floodplain and Boggy Plain (a backswamp of the South Alligator River). Ground surveys indicated that aerial surveys under-estimated abundance; based on rough correction factors calculated from ground surveys, peak numbers on the five floodplains were estimated at about 24 000. Blacknecked Storks were seen in low numbers on all floodplains, and did not vary significantly in abundance throughout the year. The total population was estimated at about 1800 birds.