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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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Record number 422545
Title Natural and human-induced predation on Cape Cormorants at Dyer Island
Author(s) Voorbergen, A.; Boer, W.F. de; Underhill, L.G.
Source Bird Conservation International 22 (2012)1. - ISSN 0959-2709 - p. 82 - 93.
DOI http://dx.doi.org/10.1017/S0959270912000032
Department(s) Resource Ecology
PE&RC
Publication type Refereed Article in a scientific journal
Publication year 2012
Keyword(s) arctocephalus-pusillus-pusillus - south-africa - larus-argentatus - seabird predation - human disturbance - fur seals - availability - population - refuse - chicks
Abstract To develop conservation strategies for vulnerable seabird species that need attention, it is important to know which factors influence their breeding productivity. Predation of eggs and chicks can have large influences on seabird reproduction, especially when human disturbance facilitates predation. On Dyer Island, Kelp Gulls Larus dominicanus prey on Cape Cormorant Phalacrocorax capensis eggs and chicks, whereas Cape fur seals Arctocephalus pusillus pusillus prey on Cape Cormorant fledglings in the waters surrounding the island. Kelp Gulls were estimated to predate 3.8% of the total number of Cape Cormorant eggs and 2.0% of the chicks on the island. These percentages can be expressed as a loss of 4.8% of Cape Cormorant fledglings, which is low compared to the estimated 24.3% mortality of Cape Cormorant fledglings by Cape fur seal predation. Human disturbance facilitated Kelp Gull egg and chick predation and increased the mobbing of cormorant fledglings by Kelp Gulls. Cormorant egg predation by gulls was more frequently reported in the late afternoon. Seal predation was more abundant at the northern side of the island compared to the southern side, was recorded more frequently in the morning, and increased through the breeding season. The altered abundance and distribution of prey, the availability of suitable breeding habitat and mortality from avian cholera, have also influenced the Cape Cormorant’s population size. Hence, the possibility that Cape Cormorants may be locked in a predator-pit, where seals and gulls prevent the population from increasing in size, needs further attention.
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