POPULATION, BIOMETRICS AND MOVEMENTS OF THE SANDERLING CALIDRIS ALBA IN SOUTHERN AFRICA

Summary

Summers, R. W., Underhill, L. G, Waltner, M. & Whitelaw, D. A. 1987. Population, biometrics and movements of the Sanderling Calidris alba in southern Africa. Ostrich 58:24-39.

The Sanderling in southern Africa is restricted to coastal habitats. The population during the austral summer was estimated to be 78000. Highest densities occurred along the west coast where the Benguela Up-welling System gives rise to enriched inter-tidal invertebrate communities, partly through the stranding of large kelps. Immigration from the breeding areas took place during September and November. Numbers were highest during mid summer and emigration took place in April. The summer population at Lange-baan Lagoon was biased towards males (72%). The percentage of first-year birds in the summer population fluctuated on a three-year cycle, coinciding with the lemming cycle in the Taimyr Peninsula in Siberia. It is suggested that the cyclic fluctuation is caused by Arctic Foxes, and perhaps other predators, feeding on lemmings in years of lemming abundance but subsisting on the eggs and chicks of birds when lemmings are scarce. First-year birds are similar in size (similar bill lengths) to older birds, but are lighter in mass during the summer. First-year birds do not accumulate the large fat reserves which older birds deposit between March and early May for northward migration. However, not all first-year birds remain in southern Africa. Trie 13000 km northward migration is completed within seven weeks and probably involves three long flights and two periods of replenishing fat reserves. Birds cross the Sahara to the Mediterranean, and also pass through the Caspian Sea to Siberia or through the North Sea coasts to either Siberia or Greenland. Return routes also involve the North, Caspian and Black Seas but there is little information about routes through Africa.