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

Waterbird counts at Rietvlei, a freshwater wetland in the Western Cape, wer e 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 ferru ginea, being the most abundant species in all years, except in the 1960s an d 1950s when Red-knobbed Coots, Fulica cristata, and Ruffs, Philomachus pug nax, outnumbered them respectively. Red-knobbed Coots and Yellow-billed Duc ks, Anas undulate, were the most numerous species during winter in all year s. 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 in crease in abundance of several species is attributed to changes in the wate r regime and habitat availability at the wetland. In terms of waterbird abu ndance, Rietvlei is the most important temporary vlei in the Western Cope a nd it ranks 16th in terms of waterbird abundance compared with all South Af rican coastal and inland wetlands for which counts are available. In the li ght of Rietvlei being proclaimed a nature reserve, a conservation managemen t plan for the area is discussed.