Long-term trends, seasonal abundance and energy consumption of waterbirds at Rietvlei, Western Cape, South Africa, 1950–1997

Abstract

Waterbird counts at Rietvlei, a freshwater wetland in the Western Cape, were analysed for four periods: 1950–56, 1961–67, 1980–85 and 1992–97. Ninety-eight species of waterbirds were recorded during these counts. Palaearctic migrants predominated during summer, with Curlew Sandpipers, Calidris ferruginea, being the mast abundant species in all years, except in the 1960s and 1950s when Red-knobbed Coots, Fulica cristata, and Ruffs, Philomachus pugnax, outnumbered them respectively. Red-knobbed Coots and Yellow-billed Ducks, Anas undulata, were the most numerous species during winter in all years. The numbers of waterbirds at Rietvlei have shown a progressive increase since the 1950s, reaching over 8300 birds in the mid-summer of 1997. The increase in abundance of several species is attributed to changes in the water regime and habitat availability at the wetland. In terms of waterbird abundance, Rietvlei is the most important temporary vlei in the Western Cape and it ranks 16th in terms of waterbird abundance compared with all South African coastal and inland wetlands for which counts are available. In the light of Rietvlei being proclaimed a nature reserve, a conservation management plan for the area is discussed.