Factors influencing growth of the African penguin colony at Boulders, South Africa, 1985-1999

This paper reports on growth of the Boulders colony of African penguins Sph eniscus 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 Engrauli s capensis off South Africa. In December 1996. penguins were excluded From a portion of land where they had formerly bred. They responded by increasin g the density of their nests in other areas and expanding their area of bre eding longshore. These patterns indicate that food and not space are curren tly controlling colony growth rate. Much of the colony growth probably resu lts from immigration of first-time breeders from other colonies. Of immigra nts, 70-80% may be from Dyer Island to the south-east, where numbers of pen guins have decreased. Boulders also is Frequently visited by penguins from other colonies, and by rehabilitated birds.