Breeding and moult phenology of African penguins Spheniscus demersus at Dassen Island

Abstract

The breeding and moult phenology of African penguins Spheniscus demersus at Dassen Island form part of a variable annual cycle. Between 1994 and 2006, African penguins bred throughout the year. Most of this period was characterised by favourable feeding conditions. There were definite peaks in breeding activity, but these varied between years and between colonies on the island, with no obvious seasonal pattern. Synchronisation of breeding activities was greater in colonies with higher nest densities, suggesting that breeding phenology  was influenced more by social interaction between individuals than by a wider-scale seasonal effect. Moult phenology of African penguins at  Dassen Island was more synchronous and seasonal than breeding  activities. Most penguins moulted between September and January. A large proportion (30%) of moult records was of birds moulting in nest sites rather than at landing beaches along the shore. The incidence of nest moulting was greatest from August to October, when sea conditions were generally rougher. The interval between successive moults ranged from 221 days to 546 days, with a mean of 349 days. The much greater degree of synchronisation in moult compared with breeding patterns suggests that moult, and not breeding, may represent the key driver of the annual cycle.

Keywords: African penguin, annual cycle, breeding phenology, Dassen Island, moult phenology, Spheniscus demersus

African Journal of Marine Science 2009, 31(2): 119–132