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

Abstract

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.

Nest survival in year‐round breeding tropical red‐capped larks Calandrella cinerea increases with higher nest abundance but decreases with higher invertebrate availability and rainfall

“…The shaded area represents the 95% confidence interval. 9 by parents (Radford et al 2001, Arlettaz et al 2010, Öberg et al 2015, Rishworth and Pistorius 2015, leaving nests more vulnerable to both harsh weather conditions and exposure to nest predators (Rishworth and Pistorius 2015). Our finding of reduced daily nest survival rates of redcapped larks with higher flying invertebrate biomass, again in contrast with our expectations, may be due to the activity and detectability of these invertebrates, the primary food of red-capped lark nest predators, as earlier discussed.…”

Energetic consequences of time‐activity budgets for a breeding seabird

“…). This increased amount of time spent flying is likely to be a result of adults needing to make regular foraging trips to provision chicks (Rishworth & Pistorius, ). In contrast, during incubation, foraging trips are less frequent due to the need for adult kittiwakes only to meet their own energy requirements (Ponchon et al ., ).…”

Variability in the Foraging Distribution and Diet of Cape Gannets between the Guard and Post-guard Phases of the Breeding Cycle

“…The distribution of its breeding colonies is limited to five islands on the west coast of South Africa and Namibia, and a single island off South Africa's south coast (Crawford et al, 2007). A pair generally produces a single offspring (Jarvis, 1974;Rishworth and Pistorius, 2015) and alternate periods of nest attendance and foraging during incubation and the early stages of chick rearing (Bijleveld and Mullers, 2009;Mullers and Tinbergen, 2009). However, when the chick is around 40-50 days old, the transition between the guard and post-guard phase takes place and both parents start spending progressively longer periods simultaneously at sea, returning to the nest for brief periods to feed the chick (Nelson, 1978;Rishworth et al, 2014b).…”