Factors influencing growth of the African penguin colony at Boulders, South Africa, 1985-199

Abstract

This paper reports on growth of the Boulders colony of African penguins Spheniscus demersus from inception in 1985 to the present. More than 900 pairs now breed there. Growth of the colony slowed in 1995 and 1996 and reversed in 1998, coinciding with periods of low abundance of Cape anchovy Engraulis capensis off South Africa. In December 1996, penguins were excluded from a portion of land where they had formerly bred. They responded by increasing the density of their nests in other areas and expanding their area of breeding longshore. These patterns indicate that food and not space are currently controlling colony growth rate. Much of the colony growth probably results from immigration of first-time breeders from other colonies. Of immigrants, 70-80% may be from Dyer Island to the south-east, where numbers of penguins have decreased. Boulders also is frequently visited by penguins from other colonies, and by rehabilitated birds.