Living on the bare edge: fitness consequences for Cape Gannets Morus capensis at Bird Island, Algoa Bay

Abstract

Avian breeding colonies often suffer high levels of predation along their margins. Nest predation is a major fitness concern for parents and therefore nests inside of the colony edge might be at a premium. This was tested through studying the colonial breeding seabird, the Cape Gannet Morus capensis, at Bird Island, Algoa Bay, South Africa. We found that breeding success is much lower for nests on the edge. Consequently, we tested whether birds nesting inside the colony had shorter foraging trips and higher nest attendance than birds along the colony edge. Although nest attendance averaged slightly less along the colony edge, the difference was not significant. Nest predation was found to be the likely cause of the higher nest failure along the colony edge. Nest positioning in Cape Gannets clearly has a profound influence on fitness, especially as the Cape Gannet appears to display a high level of nest-site fidelity.

Keywords:

• Agulhas
• breeding success
• foraging behaviour
• seabirds