THE ECOLOGICAL ROLE OF THE RED-KNOBBED COOTFULICA CRISTATAGMELIN AT THE BOT RIVER ESTUARY SOUTH AFRICA: A PRELIMINARY INVESTIGATION

Abstract

SUMMARY The red-knobbed coot Fulica cristata constitutes over 90% of the waterfowl numbers at the Bot River estuary, South Africa. In order to determine the impact of the birds on the submerged aquatic macrophytes at the estuary, aspects of the bioenergetics of the red-knobbed coot were studied. Captive birds of mean mass 720,4 g had a daily metabolized energy of 516 kJ per bird. The daily energy expenditure of the coots in the wild was estimated to be 691 kJ per bird. The birds assimilated 57,9% of their gross energy intake when feeding on Ruppia maritima L. and Potamogeton pectinatus L. and consumed approximately 82,4 g dry weight of macrophyte per bird per day during free existence. On the basis of their energy requirements, it is estimated that the coot population on the Bot River estuary consumed 759,5 tonnes dry weight, approximately 9,9-12,5% of the submerged macrophyte production in 1980–1981. Guano released into the water during the same period is estimated at 470,1 tonnes dry weight.