ESR 12:193-202 (2010)  -  DOI: https://doi.org/10.3354/esr00306

Foraging behaviour of Cape gannets as an indicator of colony health status

Ralf H. E. Mullers1,2,*, René A. Navarro2

1University of Groningen, Department of Behavioural Biology, PO Box 14, 9750 AA Haren, The Netherlands
2Animal Demography Unit, Department of Zoology, University of Cape Town, Rondebosch 7701, South Africa

ABSTRACT: From 2003 to 2007, a total of 646 breeding Cape gannets Morus capensis were equipped with GPS-loggers at 2 colonies to obtain insight into how the foraging behaviour of gannets varied between colonies and whether it could predict the ‘health’ of these colonies, i.e. the growth rate. The foraging behaviour of gannets from Malgas Island, South Africa, varied considerably during the breeding season; average trip duration could double from week to week. At Ichaboe Island, Namibia, foraging behaviour varied less, but the gannets made 2.3 h longer trips and had a larger foraging area than the gannets from Malgas. Gannets scavenging for fishery discards made shorter foraging trips and spent less time flying than birds foraging for live prey. Utilisation of fishery discards was more prominent at Malgas. Chicks from Ichaboe grew faster and had higher survival rates, possibly associated with the larger proportion of live prey in their diet. The fraction of time flown during foraging trips was positively associated with chick growth in the colony, probably because gannets that made longer trips were more likely to return with good quality live prey. Variations in food availability, fitness trade-offs, predation pressures and inter-individual specialisation might explain why our results contradict a previously described relationship between parental foraging behaviour and colony status. The study of parental behaviour is important to explain chick growth, a component of colony health status, but it is inadequate to predict overall colony health status in Cape gannets.


KEY WORDS: Population dynamics · Foraging behaviour · Chick growth · Conservation · Diet


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Cite this article as: Mullers RHE, Navarro RA (2010) Foraging behaviour of Cape gannets as an indicator of colony health status. Endang Species Res 12:193-202. https://doi.org/10.3354/esr00306

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