Long-term trends, seasonal abundance and energy consumption of waterbirds at Strandfontein, Western Cape, South Africa, 1953-1993

Waterbird counts at Cope Frats Sewage Treatment Works (Strandfontein) near Cope Town are analysed for three periods: 1953-58, 1961-67 and 1983-93. Inf ormation on waterbird abundance is also provided for the period 1979-81. On e hundred and one species; of waterbirds were recorded. Resident birds pred ominated during summer end: winter in all years. Lesser Flamingo, Phoenicop terus minor, and Red-knobbed: Coot, Fulica cristata, were the most abundant species in the 1950, Cope Teal; Anas capensis, and Greater Flamingo, Phoen icopterus ruber; in the 1960s, and Cope Carmorant, Phalacrocorax capensis i n the 1980s-90s. The total avian biomass in the 1980s-90s was 62-fold highe r compared with the 1950s, reflecting the increased abundance of many birds . in the 1980s-90s, the seasonal pattern of bird biomass paralleled that of bird abundance reaching its peak in January and declining, to ifs lowest v alue in October. The summer daily energy intake of the entire bird assembla ge exceeded that of winter in all years except in 1980s-90s. The invertebra te feeders, were the most important consumers in the 1980s-90s with the Gre ater Flamingo being responsible far the increased energy intake in late sum mer. The abundance of waterbirds increased progressively from the 1950s, re aching on average maximum of over 23 300 individuals in January during the 1980s-90s. Seventeen species were absent or recorded sporadically at Strand fontein in the 1950s compared with the 1980s-90s. Twenty-five species incre ased their abundance 10-90-fold, seven 100-600-fold, and one almost 2000-fo ld in the 1980s-90s compared with the 1950s. Lesser Flamingo was the only s pecies for which a considerable reduction in numbers was recorded. The incr ease in abundance of several species is attributed to changes in habitat av ailability, especially on increase in the water-surface area. The fluctuati ons in numbers between years is linked to changes in the sewage work system in the late 1970s, which altered water quality in the ponds and probably e ffected the food supply for some of the species. Strandfontein ranks fifth in terms of waterbird abundance compared with other South African wetlands and requires immediate conservation action.