SEASONAL ABUNDANCE AND DISTRIBUTION OF BIRDS ON THE SWARTKOPS ESTUARY, PORT ELIZABETH

Abstract

Martin, A. P. & Baird, D. 1987. Seasonal abundance and distribution of birds on the Swartkops estuary, Port Elizabeth. Ostrich 58:122-134. Counts of estuarine birds were made on the Swartkops estuary, Port Elizabeth, between September 1983 and August 1985. Seasonal variations in the numbers of both migrant and resident species were investigated; in the austral summer, over 4000 birds were recorded, whereas in winter, fewer than 1200 birds were counted. Five species made up 74% of the total number of birds: Kelp Gulls Larus dominicanus (21%), Grey Plovers Pluvialis squatarola (21%), Whimbrels Numenius phaeopus (12%), Common Terns Sterna hirundo (10%) and Curlew Sandpipers Calidris ferruginea (10%). The majority of birds (92%) were recorded on the intertidal mud and sand, and a positive correlation was found between bird density and the biomass of a major prey species, Upogebia africana. The avifauna of the estuary has changed considerably since the beginning or this century, probably reflecting long-term trends in the bird populations.