BRANTA — Richard Brian Sherley
Factors influencing the demography of Endangered seabirds at Robben Island, South Africa: Implications and approaches for management and conservation
Institution: University of Bristol, UK
Supervisors: Peter Barham, Innes Cuthill, Neill Campbell, Les Underhill
Details: PhD 2010 (Completed)
Address: Animal Demography Unit, Department of Zoology, University of Cape Town, Private Bag, Rondebosch, 7701, South Africa (Jan 2013) Email
Subject Keywords: Population ecology, breeding success, conservation biology, animal biometrics, nesting habitat, Fisheries-seabird interactions
Species Keywords: African Penguin Spheniscus demersus, Bank Cormorant Phalacrocorax neglectus
Abstract
The African penguin Spheniscus demersus and the bank cormorant Phalacrocorax neglectus are endemic to the Benguela Upwelling System and are both currently Endangered. Here, parameters relating to their breeding productivity on Robben Island, South Africa, are assessed and put into the perspective of seabird conservation in the region. In addition, the development of a novel monitoring tool, designed to assess variables like adult survival rates and colony attendance in African penguins, is described.
The breeding success of African penguins oiled in 2000 was reduced relative to control pairs, with the impact of oiling still evident nearly a decade after exposure. In contrast, birds translocated at the time of the spill had similar success to controls, supporting the importance of this action in future large oil spills. Breeding success was improved in nests located in buildings and in artificial nests, vindicating the use of the latter as a conservation tool. In addition, nest success was positively related to the annual fisheries catch of anchovy Engraulis encrasicolus made in the vicinity of Robben Island, highlighting the importance of local food availability to breeding African penguins.
Assessments of spatial and temporal variations in penguin chick growth at five colonies in South Africa supported the notion that feeding conditions can vary unpredictably within and between years and are not always similar at colonies in close proximity. Growth was poorer during periods of population decline and appeared to be related to the abundance of sardine Sardinops sagax in the previous November, suggesting a need for adults to attain adequate condition prior to breeding.
Breeding success of bank cormorants was lower at Robben Island compared to Mercury Island, Namibia, with failures related to air temperatures and wave heights, particularly when major storm events coincided with peak breeding activity. In light of the threat of climate change, this study emphasises the need for long-term monitoring programmes on this species.
Evaluation of a non-invasive, computer-vision system, designed to monitor African penguins, found baseline capacity to be 13% of birds passing a fixed point, with high levels of enrolment and recapture suggested from theoretical expansion. The system was deemed suitable for long-term monitoring and will greatly increase the quality and quantity of data available for population and behavioural analyses.
Finally, ideas for future research projects and management focus are proposed to ensure the sustainablility of Robben Island as an important seabird colony.
Published Papers
Sherley, R.B., Underhill, L.G., Barham, B.J., Barham, P.J., Coetzee, J.C., Crawford, R.J.M., Dyer, B.M., Leshoro, T.M. and Upfold, L. In press. Influence of local and regional prey availability on breeding performance of African penguins Spheniscus demersus. Marine Ecology Progress Series.
Sherley, R.B., Barham, B.J., Barham, P.J., Leshoro, T.M. and Underhill, L.G. 2012. Artificial nests enhance the breeding productivity of African Penguins (Spheniscus demersus) on Robben Island, South Africa. Emu 112: 97-106.
Sherley, R.B., Ludynia, K., Underhill, L.G., Jones, R. and Kemper, J. 2012. Storms and heat limit the nest success of Bank Cormorants: implications of future climate change for a surface-nesting seabird in southern Africa. Journal of Ornithology 153: 441-455.