THE BIOMASS, ENERGY CONSUMPTION AND BREEDING OF WATERBIRDS RELATIVE TO HYDROLOGICAL CONDITIONS AT LAICX ST LUCIA

Summary

Berruti, A. 1983. The biomass, energy consumption and breeding of waterbirds relative to hydrological conditions at Lake St Lucia. Ostrich 54:65-82.

Responses of the waterbird populations to highly variable hydrological conditions at Lake St Lucia are investigated. During high-rainfall years, summer floods are fallowed by a winter drop in water levels (drydown). During low-rainfall years water level changes are less predictable. Numbers were low after the summer hood but increased as water levels dropped and then declined as water levels stabilized. High densities of waterbirds exploit seasonally drying, highly productive marginal areas, where food is concentrated in isolated receding pools. Prolonged drydown results in drying of most marginal areas, with a resultant decrease in total waterbird numbers. Fishes appear to be a more stable food resource to waterbirds than invertebrates or plants. The breeding of piscivores is more evenly spread throughout the year compared to other bird species. Most herbivores and invertebrate-feeders are largely ground nesters, breed during the drydown, and feed by wading, or at the surface by other methods. The occurrence and breeding of White Pelicans and Greater Flamingoes is examined in greater detail because of their abundance. The estimated crude and ecological energy consumptions during the study period were 340 and 1937 kl/m²/y respectively. Management recommendations for maximum species richness and breeding success are given.