Factors impacting the breeding success of African penguins Spheniscus demersus on Robben Island

Abstract

The African penguin Spheniscus demersus is a seabird endemic to the south-western coast of Africa and can be found in three main breeding localities; southern Namibia, the Western Cape and Algoa Bay, Eastern Cape, South Africa. The African penguin has been listed as Endangered since 2010, having experienced a decline in population of more than 50% over the past three generations. This study was conducted at the breeding colony on Robben Island, South Africa, and examined two factors that have the potential to affect breeding success of African penguins; body mass at the onset of breeding and the suitability of various nest types to mitigate changing climatic conditions. Body mass was measured by recording weights using an automated weighing scale set up in front of a nest. Weights were taken at the start of breeding of each penguin in a breeding pair and these weights were compared to the number of chicks fledged, fledging period, hatching success, clutch size, and chick fledging weight. Hatching success, clutch size, and fledging weight were not influenced by the mass of either parent. There was a trend of shorter fledging periods as the mass of the heavier parent increased. The greatest effect was from the body mass of the lighter parent on the number of chicks that fledged from the nest; as the mass of the lightest adult increased, more chicks were fledged. If the lighter adult weighed below 2 kg there were always no chicks at the nest that fledged. This suggests evidence for a carry-over effect of body mass from the time before breeding starts into the breeding season, and highlights the importance of food availability for African penguins on a global scale, and not just a local one. The proportion of nest failures of six nest types (vegetation, open, natural burrow, building, wooden nest box, and artificial fibreglass burrow) at the incubation and chick-rearing stage were compared to rainfall and maximum temperature.