Protection and provisioning: the role of parental behaviour in terms of chick growth and survival in a pelagic seabird

Long-lived organisms maximise lifetime reproductive output by shifting the negative effects of temporal environmental variability onto their offspring while maintaining adult survival. Amongst seabirds, chick growth and survival could be influenced by a range of factors, including prey delivery and parent behaviour as well as predation and exposure to adverse weather conditions. In this study, an automated method of recording adult Cape gannet Morus capensis timeactivity budgets by means of new generation VHF technology was used to relate their behaviour to chick growth and survival at Bird Island, Algoa Bay, South Africa, across 2 breeding seasons ( 2011-2012 and 2012-2013). Using one of the most comprehensive datasets of breeding seabird foraging effort, we showed that, although chick growth was predominantly associated with age, parents which made shorter foraging trips clearly raised chicks which grew faster. Chick survival varied greatly between the 2 seasons ( 40 versus 97%), which was explained by different levels of nest non-attendance by parents. Chicks in the 2011-2012 season which were exposed to longer periods of non-attendance were particularly vulnerable to unseasonal storms and they were also more vulnerable to kelp gull Larus dominicanus predation while young. In contrast to Cape gannets in the declining west coast populations, chick survival at Bird Island was primarily related to parental protection rather than food provisioning rate, which probably reflects favourable foraging conditions along the southern coast of South Africa. This study highlights the importance of understanding the interplay between factors affecting chick growth and survival for the effective conservation of threatened seabird populations.